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Dr. Ahmad Omar
University of Florida

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0 Transformation
0 Disease Resistance
0 Plant biotechnology
0 Plant biochemistry

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Disease Resistance
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Research article
Published: 02 July 2021 in Phytopathology®
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Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is one of the most devastating citrus diseases worldwide. Generating disease-resistant citrus varieties is considered one of the most efficient and environmentally friendly measures for controlling canker. Xcc causes canker symptoms by inducing the expression of canker susceptibility gene LOB1 via PthA4, a transcription activator-like (TAL) effector, by binding to the effector binding element (EBE) in the promoter region. In previous studies, canker-resistant plants were generated by mutating the coding region or the EBE of LOB1. However, homozygous or biallelic canker-resistant plants have not been generated for commercial citrus varieties, such as grapefruit (C. paradisi), which usually contain two alleles of LOB1 and thus have two types of LOB1 promoter sequences: TI LOBP and TII LOBP. Two different sgRNAs were used to target both EBE types. Both 35S promoter and Yao promoter were used to drive the expression of SpCas9p to modify EBEPthA4-LOBP in grapefruit. Using ‘Duncan’ grapefruit epicotyls as explants, 19 genome-edited grapefruit plants were generated with one biallelic mutant line (#DunYao7). Xcc caused canker symptoms on wild-type and non-biallelic mutant plants but not on #DunYao7. XccPthA4 mutant containing the designer TAL effector dLOB1.5, which recognizes a conserved sequence in both wild-type and #DunYao7, caused canker symptoms on both wild-type and #DunYao7. No off-target mutations were detected in #DunYao7. This study represents the first time that CRISPR-mediated genome editing has been successfully used to generate disease-resistant plants for ‘Duncan’ grapefruit, paving the way for utilizing disease-resistant varieties to control canker.

ACS Style

Hongge Jia; Ahmad Omar; Vladimir Orbović; Nian Wang. Biallelic editing of the LOB1 promoter via CRISPR/Cas9 creates canker-resistant ‘Duncan’ grapefruit. Phytopathology® 2021, 1 .

AMA Style

Hongge Jia, Ahmad Omar, Vladimir Orbović, Nian Wang. Biallelic editing of the LOB1 promoter via CRISPR/Cas9 creates canker-resistant ‘Duncan’ grapefruit. Phytopathology®. 2021; ():1.

Chicago/Turabian Style

Hongge Jia; Ahmad Omar; Vladimir Orbović; Nian Wang. 2021. "Biallelic editing of the LOB1 promoter via CRISPR/Cas9 creates canker-resistant ‘Duncan’ grapefruit." Phytopathology® , no. : 1.

Journal article
Published: 22 April 2021 in Meta Gene
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Gestational diabetes mellitus (GDM) affects 1%–14% of all gestations. The importance of GDM stems from its relationship with adverse pregnancy outcomes. This study aimed to evaluate the correlations of vitamin D receptor (VDR) gene FokI polymorphisms with GDM in the Egyptian population. In a comparative case-control study, 196 pregnant women were divided into GDM and control groups (98 each group). The VDR gene FokI genotypes were determined in pregnant women under investigation. Both groups show no statistically significant difference for serum 25-hydroxy vitamin D (25-OHD) level, maternal age, gestational age in weeks, parity, and blood pressure. On the other hand, past miscarriage history, body mass index (BMI), glycated hemoglobin (HbA1c), and homeostasis model assessment for insulin resistance (HOMA-IR) were significantly higher in the GDM group vs. the control group. Genotype CC was found as a risk factor for GDM due to the increased odds ratio (OR) 3.78 [(1.57–8.62)] (P = 0.002). The risk of GDM decreased significantly with the dominant homozygous allele T in the tested polymorphism TT + TC vs. CC (OR = 0.32, 95% CI = 0.15–0.68 and p-value = 0.002). Genotype CC is associated with vitamin D deficiency [OR 14.4 (4.03–51.5), P = 0.001], and C allele is also associated with vitamin D deficiency [OR 2.35 (1.28–4.30), P = 0.005)]. There was a relationship between VDR gene FokI polymorphism and the development of GDM. Besides, a possible association exists between genotype CC and C allele and vitamin D deficiency.

ACS Style

Mohamed El-Husseny Radwan; Heba S. Taha; Abdelaleim Ismail ElSayed; Ahmad A. Omar. Evaluation of VDR gene FokI polymorphism and serum vitamin D level in gestational diabetes mellitus (Egyptian case-control study). Meta Gene 2021, 29, 100908 .

AMA Style

Mohamed El-Husseny Radwan, Heba S. Taha, Abdelaleim Ismail ElSayed, Ahmad A. Omar. Evaluation of VDR gene FokI polymorphism and serum vitamin D level in gestational diabetes mellitus (Egyptian case-control study). Meta Gene. 2021; 29 ():100908.

Chicago/Turabian Style

Mohamed El-Husseny Radwan; Heba S. Taha; Abdelaleim Ismail ElSayed; Ahmad A. Omar. 2021. "Evaluation of VDR gene FokI polymorphism and serum vitamin D level in gestational diabetes mellitus (Egyptian case-control study)." Meta Gene 29, no. : 100908.

Journal article
Published: 24 November 2020 in Metabolites
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The citrus industry at present is severely affected by huanglongbing disease (HLB). HLB is caused by the supposed bacterial pathogen “Candidatus Liberibacter asiaticus” and is transmitted by the insect vector, the Asian citrus psyllid, Diaphorina citri Kuwayama. Developing new citrus hybrids to improve HLB management is much needed. In this study, we investigated the metabolomic profiles of three new hybrids produced from the cross of C2-5-12 Pummelo (Citrus maxima (L.) Osbeck) × pollen from Citrus latipes. The hybrids were selected based on leaf morphology and seedling vigor. The selected hybrids exhibited compact and upright tree architecture as seen in C. latipes. Hybrids were verified by simple sequence repeat markers, and were subjected to metabolomic analysis using gas chromatography-mass spectrometry. The volatile organic compounds (VOCs) and polar metabolites profiling also showed that the new hybrids were different from their parents. Interestingly, the levels of stored VOCs in hybrid II were higher than those observed in its parents and other hybrids. The level of most VOCs released by hybrid II was also higher than that released from its parents. Additionally, the preference assay showed that hybrid II was more attractive to D. citri than its parents and other hybrids. The leaf morphology, compact and upright architecture of hybrid II, and its attraction to D. citri suggest that it could be used as a windbreak and trap tree for D. citri (double duty), once its tolerance to HLB disease is confirmed. Our results showed that metabolomic analysis could be successfully used to understand the biochemical mechanisms controlling the interaction of D. citri with its host plants.

ACS Style

Nabil Killiny; Shelley E. Jones; Faraj Hijaz; Abdelaziz Kishk; Yulica Santos-Ortega; Yasser Nehela; Ahmad A. Omar; Qibin Yu; Jr. Fred G. Gmitter; Jude W. Grosser; Manjul Dutt. Metabolic Profiling of Hybrids Generated from Pummelo and Citrus latipes in Relation to Their Attraction to Diaphorina citri, the Vector of Huanglongbing. Metabolites 2020, 10, 477 .

AMA Style

Nabil Killiny, Shelley E. Jones, Faraj Hijaz, Abdelaziz Kishk, Yulica Santos-Ortega, Yasser Nehela, Ahmad A. Omar, Qibin Yu, Jr. Fred G. Gmitter, Jude W. Grosser, Manjul Dutt. Metabolic Profiling of Hybrids Generated from Pummelo and Citrus latipes in Relation to Their Attraction to Diaphorina citri, the Vector of Huanglongbing. Metabolites. 2020; 10 (12):477.

Chicago/Turabian Style

Nabil Killiny; Shelley E. Jones; Faraj Hijaz; Abdelaziz Kishk; Yulica Santos-Ortega; Yasser Nehela; Ahmad A. Omar; Qibin Yu; Jr. Fred G. Gmitter; Jude W. Grosser; Manjul Dutt. 2020. "Metabolic Profiling of Hybrids Generated from Pummelo and Citrus latipes in Relation to Their Attraction to Diaphorina citri, the Vector of Huanglongbing." Metabolites 10, no. 12: 477.

Full length original research paper
Published: 08 November 2020 in Water and Environment Journal
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Thirteen bacterial isolates from a bioreactor treating a mixture of municipal and molasses wastewater were investigated for their potential to degrade and decolorize melanoidins. All isolates were initially screened for manganese peroxidase activity and growth potential in the presence of four synthetic melanoidins solutions at concentrations ranging from 3 to 7 g/L/L. Three isolates of potential manganese peroxidase producing‐bacteria two Klebsiella sp. (B2‐B3) and Escherichia coli (B4) and one strain of Lactobacillus kefiri (B1) showed high synthetic melanoidin tolerance. The 16S rDNA sequence showed that they were closely related to E. coli and Klebsiella sp. The most significant degree of decolorization was observed on day 1, reaching 60 – 67%. Furthermore, the tested strains reduced the chemical oxygen demand by more than 50% or more than 70% of the initial value with or without additional supplementation of the reaction mixture, respectively. All tested isolates showed increased ability for reducing the organic matter content of a raw melanoidin solution exceeding 65 %, favoring, therefore, the utilization potential of the isolated strains for the biological processing of molasses wastewaters. Thus, microbial decolorization could be an innovative wastewater treatment for environmental protection purposes.

ACS Style

Ahmad A. Omar; Samir Mahgoub; Ali Salama; Eleni Likotrafiti; Jonathan Rhoades; Christos Christakis; Petros Samaras. Evaluation of Lactobacillus kefiri and manganese peroxidase‐producing bacteria for decolorization of melanoidins and reduction of chemical oxygen demand. Water and Environment Journal 2020, 35, 704 -714.

AMA Style

Ahmad A. Omar, Samir Mahgoub, Ali Salama, Eleni Likotrafiti, Jonathan Rhoades, Christos Christakis, Petros Samaras. Evaluation of Lactobacillus kefiri and manganese peroxidase‐producing bacteria for decolorization of melanoidins and reduction of chemical oxygen demand. Water and Environment Journal. 2020; 35 (2):704-714.

Chicago/Turabian Style

Ahmad A. Omar; Samir Mahgoub; Ali Salama; Eleni Likotrafiti; Jonathan Rhoades; Christos Christakis; Petros Samaras. 2020. "Evaluation of Lactobacillus kefiri and manganese peroxidase‐producing bacteria for decolorization of melanoidins and reduction of chemical oxygen demand." Water and Environment Journal 35, no. 2: 704-714.

Journal article
Published: 06 July 2020 in Plants
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Melatonin improves the tolerance of plants to various environmental stresses by protecting plant cells against oxidative stress damage. The objective of the current study was to determine whether exogenous melatonin (MT) treatments could help protecting peanut (Arachis hypogaea) seedlings against salinity stress. This was achieved by investigating enzymatic and non-enzymatic antioxidant systems and the expression of melatonin biosynthesis related genes in response to salinity stress with or without exogenous MT. The results showed a significant increase in the concentrations of reactive oxygen species (ROS) in peanut seedlings under salinity stress. The exogenous application of melatonin decreased the levels of ROS through the activation of antioxidant enzymes in peanut seedlings under salinity stress. Transcription levels of melatonin biosynthesis related genes such as N‐acetylserotonin methyltransferase (ASMT1, ASMT2, ASMT3), tryptophan decarboxylase (TDC), and tryptamine 5‐hydroxylase (T5H) were up-regulated with a 150 µM melatonin treatment under salinity stress. The results indicated that melatonin regulated the redox homeostasis by its ability to induce either enzymatic or non-enzymatic antioxidant systems. In addition, phylogenetic analysis of melatonin biosynthesis genes (ASMT1, ASMT2, ASMT3, TDC, T5H) were performed on a total of 56 sequences belonging to various plant species including five new sequences extracted from Arachis hypogaea (A. hypogaea). This was based on pairwise comparison among aligned nucleotides and predicted amino acids as well as on substitution rates, and phylogenetic inference. The analyzed sequences were heterogeneous and the A. hypogaea accessions were primarily closest to those of Manihot esculenta, but this needs further clarification.

ACS Style

Abdelaleim I. Elsayed; Moncef Boulila; Mohammed S. Rafudeen; Azza H. Mohamed; Sonali Sengupta; Mostafa Rady; Ahmad A. Omar. Melatonin Regulatory Mechanisms and Phylogenetic Analyses of Melatonin Biosynthesis Related Genes Extracted from Peanut under Salinity Stress. Plants 2020, 9, 854 .

AMA Style

Abdelaleim I. Elsayed, Moncef Boulila, Mohammed S. Rafudeen, Azza H. Mohamed, Sonali Sengupta, Mostafa Rady, Ahmad A. Omar. Melatonin Regulatory Mechanisms and Phylogenetic Analyses of Melatonin Biosynthesis Related Genes Extracted from Peanut under Salinity Stress. Plants. 2020; 9 (7):854.

Chicago/Turabian Style

Abdelaleim I. Elsayed; Moncef Boulila; Mohammed S. Rafudeen; Azza H. Mohamed; Sonali Sengupta; Mostafa Rady; Ahmad A. Omar. 2020. "Melatonin Regulatory Mechanisms and Phylogenetic Analyses of Melatonin Biosynthesis Related Genes Extracted from Peanut under Salinity Stress." Plants 9, no. 7: 854.

Journal article
Published: 10 May 2020 in Journal of Biotechnology Research
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Silymarin is a polyphenolic flavonoid mixture isolated from milk thistle which is believed to be responsible for the plant’s hepatoprotective action. Silymarin is hepatoprotective flavonoid drug available as bio marker in Silybun marianum (common name milk thistle). Silymarin is being used in treatment of various liver disease of different etiology because of its hepatoprotective action. Phytochemicals are playing a vital role for the treatment of different types of diseases and still used in both traditional and modern medication system. The phytochemical analysis of milk thistle seeds extract indicated that the plant is rich in secondary compounds. The results revealed that milk thistle seeds contain high amount of total phenolic, flavonoid and antioxidant compounds. The antibacterial activities of the ethanol seeds extract of milk thistle was tested against Gram-positive bacteria (Staphylococcus aures) and Gram-negative bacteria (Salmonella entirica). Antibacterial effects of crude extract were performed using modified Kirby-Bauer disc diffusion technique to determine the zone of inhibition. The results demonstrated that ethanol seeds extract of milk thistle is shown strong inhibition zone against Staphylococcus aures and Salmonella entirica compared to the control. Also, milk thistle seeds extract showed highly anticancer activity. This medicinal plant could be developed into affordable and safe standardized herbal products and may serve as a source of new molecules for broad-spectrum anticancer, antimicrobial agents.

ACS Style

Basma S. M. Ali; Abdelaleim I. Elsayed; Mahmoud A. Doheem; Ahmed M. Abo Eita; Ahmad Omar. Effect of Milk Thistle (Silybum marianum (L.) Gaertn) Seed Extract on Bacterial Activities and Growth of Human Liver Cancer Cells. Journal of Biotechnology Research 2020, 27 -33.

AMA Style

Basma S. M. Ali, Abdelaleim I. Elsayed, Mahmoud A. Doheem, Ahmed M. Abo Eita, Ahmad Omar. Effect of Milk Thistle (Silybum marianum (L.) Gaertn) Seed Extract on Bacterial Activities and Growth of Human Liver Cancer Cells. Journal of Biotechnology Research. 2020; (65):27-33.

Chicago/Turabian Style

Basma S. M. Ali; Abdelaleim I. Elsayed; Mahmoud A. Doheem; Ahmed M. Abo Eita; Ahmad Omar. 2020. "Effect of Milk Thistle (Silybum marianum (L.) Gaertn) Seed Extract on Bacterial Activities and Growth of Human Liver Cancer Cells." Journal of Biotechnology Research , no. 65: 27-33.

Original article
Published: 09 January 2020 in Molecular Biology Reports
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A total of 53 plant species accessions from different geographic regions, including four melatonin precursor-coding genes obtained from Arachis hypogaea (ASMT1, 2, 3 and T5H) underwent extensive molecular evolutionary analyses. Evolutionary relationships were inferred and showed that dichotomous bifurcating trees did not reflect the true phylogeny since reticulate events took place due likely to recombination. Thus, a phylogenetic network was reconstructed for each type of enzyme and highlighted the presence of such incompatibilities. GARD algorithm pointed out that ASMT1, 2, and 3-coding gene sequences contained recombination sites with significant topological incongruence on both sides of the breakpoints (for ASMT1, and 2), while only on one side of the breakpoints for ASMT3. In contrast, no statistically recombination signal was recorded in T5H-coding gene. Furthermore, gene duplication was localized in the ancestor of a monophyletic group of Populus accessions. Selection pressure was assessed using several statistical models incorporated in HyPhy package through the datamonkey web server. It was demonstrated that numerous individual sites and tree branches experienced predominantly purifying selection. In contrast, the BUSTED model evidenced a gene-wide episodic diversifying selection in the phylogeny of only three enzyme-coding genes (ASMT, and 2, and T5H). Likewise, it was shown that Mixed Effects Model of Episodic Selection (MEME) model detected only episodic positively selected sites in all four melatonin enzymes-coding genes; whereas, REL model failed to detect neither positive nor negative selection in tested individual sites of ASMT3-coding gene.

ACS Style

Moncef Boulila; Abdelaleim Ismail Elsayed; Mohammed Suhail Rafudeen; Ahmad Omar. Investigating molecular evolutionary forces and phylogenetic relationships among melatonin precursor-encoding genes of different plant species. Molecular Biology Reports 2020, 47, 1625 -1636.

AMA Style

Moncef Boulila, Abdelaleim Ismail Elsayed, Mohammed Suhail Rafudeen, Ahmad Omar. Investigating molecular evolutionary forces and phylogenetic relationships among melatonin precursor-encoding genes of different plant species. Molecular Biology Reports. 2020; 47 (3):1625-1636.

Chicago/Turabian Style

Moncef Boulila; Abdelaleim Ismail Elsayed; Mohammed Suhail Rafudeen; Ahmad Omar. 2020. "Investigating molecular evolutionary forces and phylogenetic relationships among melatonin precursor-encoding genes of different plant species." Molecular Biology Reports 47, no. 3: 1625-1636.

Journal article
Published: 16 December 2019 in Plants
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Biosynthesis and accumulation of flavonolignans in plants are influenced by different environmental conditions. Biosynthesis and accumulation of silymarin in milk thistle (Silybum marianum L.) were studied under drought stress with respect to the antioxidant defense system at the physiological and gene expression level. The results revealed a reduction in leaf chlorophyll, ascorbic acid, and glutathione contents. In contrast, H2O2, proline, and antioxidative enzyme activities, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), were increased. These results confirmed that milk thistle undergoes oxidative stress under drought stress. Furthermore, transcription levels of APX, SOD, CAT, 1-Cys-Prx, and PrxQ were significantly increased in milk thistle under drought stress. Overall this suggests that protection against reactive oxygen species and peroxidation reactions in milk thistle are provided by enzymatic and non-enzymatic antioxidants. Flavonolignans from milk thistle seeds after different drought treatments were quantified by high-performance liquid chromatography (HPLC) and showed that severe drought stress enhanced the accumulation of silymarin and its components compared with seeds from the control (100% water capacity). Silybin is the major silymarin component and the most bioactive ingredient of the milk thistle extract. Silybin accumulation was the highest among all silymarin components in seeds obtained from drought-stressed plants. The expression of the chalcone synthase (CHS) genes (CHS1, CHS2, and CHS3), which are associated with the silybin biosynthetic pathway, was also increased during drought stress. These results indicated that milk thistle exhibits tolerance to drought stress and that seed derived from severe drought-stressed plants had higher levels of silymarin.

ACS Style

Abdelaleim I. Elsayed; Mohamed A. M. El-Hamahmy; Mohammed S. Rafudeen; Azza H. Mohamed; Ahmad A. Omar. The Impact of Drought Stress on Antioxidant Responses and Accumulation of Flavonolignans in Milk Thistle (Silybum marianum (L.) Gaertn). Plants 2019, 8, 611 .

AMA Style

Abdelaleim I. Elsayed, Mohamed A. M. El-Hamahmy, Mohammed S. Rafudeen, Azza H. Mohamed, Ahmad A. Omar. The Impact of Drought Stress on Antioxidant Responses and Accumulation of Flavonolignans in Milk Thistle (Silybum marianum (L.) Gaertn). Plants. 2019; 8 (12):611.

Chicago/Turabian Style

Abdelaleim I. Elsayed; Mohamed A. M. El-Hamahmy; Mohammed S. Rafudeen; Azza H. Mohamed; Ahmad A. Omar. 2019. "The Impact of Drought Stress on Antioxidant Responses and Accumulation of Flavonolignans in Milk Thistle (Silybum marianum (L.) Gaertn)." Plants 8, no. 12: 611.

Journal article
Published: 15 December 2019 in Journal of Applied Sciences
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Impact of Dodder (Cuscuta spp.) Infestation and Gamma Radiation on Fahl Ecotype of the Egyptian Clover

ACS Style

Ahmad Omar; Ehab M. Zayed; Maha F. El-Enany; Gamal A. Abd El-Daem. Impact of Dodder (Cuscuta spp.) Infestation and Gamma Radiation on Fahl Ecotype of the Egyptian Clover. Journal of Applied Sciences 2019, 20, 14 -25.

AMA Style

Ahmad Omar, Ehab M. Zayed, Maha F. El-Enany, Gamal A. Abd El-Daem. Impact of Dodder (Cuscuta spp.) Infestation and Gamma Radiation on Fahl Ecotype of the Egyptian Clover. Journal of Applied Sciences. 2019; 20 (1):14-25.

Chicago/Turabian Style

Ahmad Omar; Ehab M. Zayed; Maha F. El-Enany; Gamal A. Abd El-Daem. 2019. "Impact of Dodder (Cuscuta spp.) Infestation and Gamma Radiation on Fahl Ecotype of the Egyptian Clover." Journal of Applied Sciences 20, no. 1: 14-25.

Original research article
Published: 07 January 2019 in Frontiers in Plant Science
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Host disease resistance is the most desirable strategy for control of citrus canker, a disease caused by a gram-negative bacterium Xanthomonas citri subsp. citri. However, no resistant commercial citrus cultivar has been identified. Cybridization, a somatic hybridization approach that combines the organelle and nuclear genomes from different species, was used to create cybrids between citrus canker resistant ‘Meiwa’ kumquat (Fortunella crassifolia Swingle snym. Citrus japonica Thunb.) and susceptible grapefruit (Citrus paradisi Macfad) cultivars. From these fusions, cybrids with grapefruit nucleus, kumquat mitochondria and kumquat chloroplasts and cybrids with grapefruit nucleus, kumquat mitochondria and grapefruit chloroplasts were generated. These cybrids showed a range of citrus canker response, but all cybrids with kumquat chloroplasts had a significantly lower number of lesions and lower Xanthomonas citri subsp. citri populations than the grapefruit controls. Cybrids with grapefruit chloroplasts had a significantly higher number of lesions than those with kumquat chloroplasts. To understand the role of chloroplasts in the cybrid disease defense, quantitative PCR was performed on both cybrid types and their parents to examine changes in gene expression during Xanthomonas citri subsp. citri infection. The results revealed chloroplast influences on nuclear gene expression, since isonuclear cybrids and ‘Marsh’ grapefruit had different gene expression profiles. In addition, only genotypes with kumquat chloroplasts showed an early up-regulation of reactive oxygen species genes upon Xanthomonas citri subsp. citri infection. These cybrids have the potential to enhance citrus canker resistance in commercial grapefruit orchards. They also serve as models for understanding the contribution of chloroplasts to plant disease response and raise the question of whether other alien chloroplast genotypes would condition similar results.

ACS Style

Mayara M. Murata; Ahmad A. Omar; Zhonglin Mou; Christine D. Chase; Jude W. Grosser; James H. Graham. Novel Plastid-Nuclear Genome Combinations Enhance Resistance to Citrus Canker in Cybrid Grapefruit. Frontiers in Plant Science 2019, 9, 1 .

AMA Style

Mayara M. Murata, Ahmad A. Omar, Zhonglin Mou, Christine D. Chase, Jude W. Grosser, James H. Graham. Novel Plastid-Nuclear Genome Combinations Enhance Resistance to Citrus Canker in Cybrid Grapefruit. Frontiers in Plant Science. 2019; 9 ():1.

Chicago/Turabian Style

Mayara M. Murata; Ahmad A. Omar; Zhonglin Mou; Christine D. Chase; Jude W. Grosser; James H. Graham. 2019. "Novel Plastid-Nuclear Genome Combinations Enhance Resistance to Citrus Canker in Cybrid Grapefruit." Frontiers in Plant Science 9, no. : 1.

Original paper
Published: 14 February 2018 in Transgenic Research
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Genetic engineering approaches offer an alternative method to the conventional breeding of Citrus sp. ‘W. Murcott’ mandarin (a hybrid of ‘Murcott’ and an unknown pollen parent) is one of the most commercially important cultivars grown in many regions around the world. Transformation of ‘W. Murcott’ mandarin was achieved by direct DNA uptake using a protoplast transformation system. DNA construct (pAO3), encoding Green Fluorescent Protein (GFP) and the cDNA of Xa21, a Xanthomonas resistance gene from rice, was used to transform protoplasts of ‘W. Murcott’ mandarin. Following citrus protoplast culture and regeneration, transformed micro calli were microscopically designated via GFP expression, physically isolated from non-transformed tissue, and cultured on somatic embryogenesis induction medium. More than 150 transgenic embryos were recovered and from them, ten transgenic lines were regenerated and cultured on rooting medium for shoot elongation. Transgenic shoots were micrografted and established in the greenhouse with 3–5 replicates per line. The insertion of Xa21 and GFP was confirmed by PCR and southern blot analysis. GFP expression was verified by fluorescence microscopy and western blot analysis revealed expression of Xa21 although it was variable among transgenic lines, as shown by RT-qPCR. Transgenic plants challenged with the citrus canker pathogen by syringe inoculation showed a reduction in lesion number and bacterial populations within lesions compared to non-transgenic control plants. Transgenic ‘W. Murcott’ mandarin lines with improved canker resistance via protoplast transformation from embryogenic callus with the Xa21 gene from rice are being evaluated under field conditions to validate the level of resistance.

ACS Style

Ahmad A. Omar; Mayara M. Murata; Hesham A. El-Shamy; James H. Graham; Jude W. Grosser. Enhanced resistance to citrus canker in transgenic mandarin expressing Xa21 from rice. Transgenic Research 2018, 27, 179 -191.

AMA Style

Ahmad A. Omar, Mayara M. Murata, Hesham A. El-Shamy, James H. Graham, Jude W. Grosser. Enhanced resistance to citrus canker in transgenic mandarin expressing Xa21 from rice. Transgenic Research. 2018; 27 (2):179-191.

Chicago/Turabian Style

Ahmad A. Omar; Mayara M. Murata; Hesham A. El-Shamy; James H. Graham; Jude W. Grosser. 2018. "Enhanced resistance to citrus canker in transgenic mandarin expressing Xa21 from rice." Transgenic Research 27, no. 2: 179-191.

Journal article
Published: 15 December 2017 in American Journal of Biochemistry and Molecular Biology
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Molecular Characterization of Soybean (Glycine max L. Merr) Genotypes Tolerant and/or Susceptible to Cotton Leaf Worm (Spodoptera littoralis)

ACS Style

Ahmad Omar; Azza Hosni Moha; Mahmoud Imam Nasr; Khalil Abdel Hame; Elsayed Abdel Khal; Ahmed Ismail Ham; Ehab Mohamed Za. Molecular Characterization of Soybean (Glycine max L. Merr) Genotypes Tolerant and/or Susceptible to Cotton Leaf Worm (Spodoptera littoralis). American Journal of Biochemistry and Molecular Biology 2017, 8, 34 -47.

AMA Style

Ahmad Omar, Azza Hosni Moha, Mahmoud Imam Nasr, Khalil Abdel Hame, Elsayed Abdel Khal, Ahmed Ismail Ham, Ehab Mohamed Za. Molecular Characterization of Soybean (Glycine max L. Merr) Genotypes Tolerant and/or Susceptible to Cotton Leaf Worm (Spodoptera littoralis). American Journal of Biochemistry and Molecular Biology. 2017; 8 (1):34-47.

Chicago/Turabian Style

Ahmad Omar; Azza Hosni Moha; Mahmoud Imam Nasr; Khalil Abdel Hame; Elsayed Abdel Khal; Ahmed Ismail Ham; Ehab Mohamed Za. 2017. "Molecular Characterization of Soybean (Glycine max L. Merr) Genotypes Tolerant and/or Susceptible to Cotton Leaf Worm (Spodoptera littoralis)." American Journal of Biochemistry and Molecular Biology 8, no. 1: 34-47.

Journal article
Published: 01 July 2017 in Plant Physiology and Biochemistry
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Huanglongbing (HLB) is currently considered the most destructive disease of citrus. Since its spread to the Americas, HLB has killed millions of trees and caused a sharp decline in production in many citrus growing regions. With the continuous spread of HLB disease in Florida and worldwide, there is an urgent need for the development of commercial citrus cultivars with a strong tolerance to HLB. Interestingly, field observations showed that some of the recently released mandarin hybrids such as 'Sugar Belle' were tolerant to HLB. In this study, we investigated the volatile and non-volatile metabolites of greenhouse-grown 'Sugar Belle' mandarin and four of its ancestors in order to understand why 'Sugar Belle' mandarin is relatively tolerant to HLB. Leaf volatiles were directly extracted with hexane and analyzed using gas chromatography-mass spectrometry (GC-MS). Leaf polar metabolites were extracted with a mixture of methanol:water (1:1, v/v), derivatized to their trimethylsilyl ethers, and analyzed using GC-MS. Forty-seven volatile compounds and forty-two polar metabolites were detected in 'Sugar Belle' mandarin leaves and its ancestors. 'Sugar Belle' was high in several volatiles such as α-thujene, para-cymene, γ-terpinene, thymol, β-elemene, and (E)-β-caryophyllene. Some of these volatiles, especially thymol, β-elemene, and (E)-β-caryophyllene are known for their anti-microbial activity. In addition, 'Sugar Belle' mandarin was the highest in synephrine, benzoic acid, ferulic acid, caffeic acid, chiro-inositol, fructose, glucose, threonic acid, saccharic acid, and galactaric acid, and the second in threonine, malic acid, and myo-inositol compared to the ancestors. Phenolic compounds such as benzoic, ferulic, and caffeic acids may act as antibacterial agents, whereas others like sugar alcohols may protect 'Sugar Belle' mandarin from stress during pathogen attack. The tolerance of 'Sugar Belle' and other newly released mandarin hybrids should be further evaluated using greenhouse controlled studies. If tolerance of these hybrids is confirmed, they could be used to replace the traditionally susceptible cultivars.

ACS Style

Nabil Killiny; Maria Filomena Valim; Shelley E. Jones; Ahmad Omar; Faraj Hijaz; Fred G. Gmitter; Jude W. Grosser. Metabolically speaking: Possible reasons behind the tolerance of ‘Sugar Belle’ mandarin hybrid to huanglongbing. Plant Physiology and Biochemistry 2017, 116, 36 -47.

AMA Style

Nabil Killiny, Maria Filomena Valim, Shelley E. Jones, Ahmad Omar, Faraj Hijaz, Fred G. Gmitter, Jude W. Grosser. Metabolically speaking: Possible reasons behind the tolerance of ‘Sugar Belle’ mandarin hybrid to huanglongbing. Plant Physiology and Biochemistry. 2017; 116 ():36-47.

Chicago/Turabian Style

Nabil Killiny; Maria Filomena Valim; Shelley E. Jones; Ahmad Omar; Faraj Hijaz; Fred G. Gmitter; Jude W. Grosser. 2017. "Metabolically speaking: Possible reasons behind the tolerance of ‘Sugar Belle’ mandarin hybrid to huanglongbing." Plant Physiology and Biochemistry 116, no. : 36-47.

Plant tissue culture
Published: 27 April 2017 in In Vitro Cellular & Developmental Biology - Plant
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Cybrid production, combining the nucleus of one species with alien cytoplasmic organelles of another, is a potentially valuable method used for improvement of various crops including Citrus species. Furthermore, this technology is considered a non-GMO biotechnology strategy. In citrus, cybrid plants can be produced as a by-product of somatic fusion. Host resistance is the most desirable strategy for control of citrus canker. By using a cybridization approach, several putative cybrids were created by protoplast fusion of embryogenic suspension culture-derived protoplasts of canker resistant ‘Meiwa’ kumquat (Citrus japonica Thunb), with mesophyll-derived protoplasts of three grapefruit (Citrus paradisi Macfad.) cultivars ‘Marsh,’ ‘Flame,’ and ‘N11-11’ somaclone of ‘Ruby Red.’ In an effort to generate new grapefruit cultivars with enhanced canker resistance, putative cybrid grapefruit plants morphologically equivalent to standard grapefruit from all three combinations were produced. Four mitochondrial (mt) introns, a mt ribosomal RNA spacer region, and four chloroplast (cp) DNA regions previously shown to have polymorphism among different Citrus species were tested. Four molecular markers, two mt DNA regions (intron nad7i2 and a rRNA spacer), and two cp DNA regions (NADH dehydrogenase subunit K (ndhk) gene and a trnG-trnR intergenic spacer) revealed polymorphism between kumquat and grapefruit and were used to validate the cybrids. All the cybrids had the mt genome of kumquat, and most had the cp genome of kumquat with a few exceptions. EST-SSR marker analysis confirmed that the nuclear genome in all the generated cybrids came from the grapefruit parent. All the cybrid clones have been propagated and are undergoing extensive canker assays to identify any clones that have improved canker tolerance/resistance. These cybrid populations provide a valuable tool for investigating the contribution of cytoplasmic organelles to plant disease resistance.

ACS Style

Ahmad A. Omar; Mayara Murata; Qibin Yu; Fred G. Gmitter; Christine D. Chase; James H. Graham; Jude W. Grosser. Production of three new grapefruit cybrids with potential for improved citrus canker resistance. In Vitro Cellular & Developmental Biology - Plant 2017, 53, 256 -269.

AMA Style

Ahmad A. Omar, Mayara Murata, Qibin Yu, Fred G. Gmitter, Christine D. Chase, James H. Graham, Jude W. Grosser. Production of three new grapefruit cybrids with potential for improved citrus canker resistance. In Vitro Cellular & Developmental Biology - Plant. 2017; 53 (3):256-269.

Chicago/Turabian Style

Ahmad A. Omar; Mayara Murata; Qibin Yu; Fred G. Gmitter; Christine D. Chase; James H. Graham; Jude W. Grosser. 2017. "Production of three new grapefruit cybrids with potential for improved citrus canker resistance." In Vitro Cellular & Developmental Biology - Plant 53, no. 3: 256-269.

Journal article
Published: 15 December 2016 in International Journal of Dairy Science
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Salah A. Khalifa; Ahmad Omar; Azza Mohamed. The Effect of Substituting Milk Fat by Peanut Oil on the Quality of White Soft Cheese. International Journal of Dairy Science 2016, 12, 28 -40.

AMA Style

Salah A. Khalifa, Ahmad Omar, Azza Mohamed. The Effect of Substituting Milk Fat by Peanut Oil on the Quality of White Soft Cheese. International Journal of Dairy Science. 2016; 12 (1):28-40.

Chicago/Turabian Style

Salah A. Khalifa; Ahmad Omar; Azza Mohamed. 2016. "The Effect of Substituting Milk Fat by Peanut Oil on the Quality of White Soft Cheese." International Journal of Dairy Science 12, no. 1: 28-40.

Journal article
Published: 15 December 2016 in American Journal of Biochemistry and Molecular Biology
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Abdelaleim ElSayed; M. Boulila; D.C. Odero; Ahmad Omar; A.M. Gomaa; R. Viswanatha. Characterization of ORF0 and ORF1 and their Roles in Recombination and Replication of Sugarcane yellow leaf virus. American Journal of Biochemistry and Molecular Biology 2016, 7, 41 -52.

AMA Style

Abdelaleim ElSayed, M. Boulila, D.C. Odero, Ahmad Omar, A.M. Gomaa, R. Viswanatha. Characterization of ORF0 and ORF1 and their Roles in Recombination and Replication of Sugarcane yellow leaf virus. American Journal of Biochemistry and Molecular Biology. 2016; 7 (1):41-52.

Chicago/Turabian Style

Abdelaleim ElSayed; M. Boulila; D.C. Odero; Ahmad Omar; A.M. Gomaa; R. Viswanatha. 2016. "Characterization of ORF0 and ORF1 and their Roles in Recombination and Replication of Sugarcane yellow leaf virus." American Journal of Biochemistry and Molecular Biology 7, no. 1: 41-52.

Book chapter
Published: 01 January 2016 in Advanced Structural Safety Studies
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The genus Citrus contains numerous fresh and processed fruit cultivars that are economically important worldwide. New cultivars are needed to battle industry threatening diseases and to create new marketing opportunities. Citrus improvement by conventional methods alone has many limitations that can be overcome by applications of emerging biotechnologies, generally requiring cell to plant regeneration. Many citrus genotypes are amenable to somatic embryogenesis, which became a key regeneration pathway in many experimental approaches to cultivar improvement. This chapter provides a brief history of plant somatic embryogenesis with focus on citrus, followed by a discussion of proven applications in biotechnology-facilitated citrus improvement techniques, such as somatic hybridization, somatic cybridization, genetic transformation, and the exploitation of somaclonal variation. Finally, two important new protocols that feature plant regeneration via somatic embryogenesis are provided: protoplast transformation and Agrobacterium-mediated transformation of embryogenic cell suspension cultures.

ACS Style

Ahmad Omar; Manjul Dutt; Frederick G. Gmitter; Jude W. Grosser. Somatic Embryogenesis: Still a Relevant Technique in Citrus Improvement. Advanced Structural Safety Studies 2016, 1359, 289 -327.

AMA Style

Ahmad Omar, Manjul Dutt, Frederick G. Gmitter, Jude W. Grosser. Somatic Embryogenesis: Still a Relevant Technique in Citrus Improvement. Advanced Structural Safety Studies. 2016; 1359 ():289-327.

Chicago/Turabian Style

Ahmad Omar; Manjul Dutt; Frederick G. Gmitter; Jude W. Grosser. 2016. "Somatic Embryogenesis: Still a Relevant Technique in Citrus Improvement." Advanced Structural Safety Studies 1359, no. : 289-327.

Journal article
Published: 10 June 2015 in African Journal of Biotechnology
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The inter-simple sequence repeat (ISSR) markers have been used in order to determine genetic variation and relationship between two clover ecotypes. Ten (10) primers for ISSR were used in this study but only six were successful in generating reproducible and reliable amplicons for different types of the Egyptian clover. The results reveal the polymorphism level by ISSR primers. HB10 ISSR-primer was higher than the rest of the ISSR primers in polymorphic 100%. The Fahl monocut ecotype had 29 present bands, 3 absent bands in total of 32 bands; among those there were two unique bands. The multicut ecotype were given different pattern of bands, Gemmiza1 (21 present and 11 absent), Giza6 (21 present and 11 absent) and Serw1; (23 present and 9 absent). There were three unique bands appearance in the two ecotypes. Fahl was given two with HB11 and HB13; the Serw1 multicut cultivar had one unique bands with HB08. Similarity indices among the four Egyptian clover cultivars based on ISSR analysis was estimated and the highest value appeared between Fahl and Gemmiza1 as well as Giza6 and Serw1 followed by Fahl and Serw1. The lowest similarity value appeared between Gemmiza1 and Serw1 followed by Gemmiza1 and Giza6. Key words: Egyptian clover, molecular marker, Fahl, Gemmiza1, Giza6, Serw1.

ACS Style

Zayed Ehab; Sayed Mervat; Omar Ahmad; Ehab Zayed#; Mervat Sayed; Ahmad Omar#. Genetic variations between two ecotypes of Egyptian clover by inter-simple sequence repeat (ISSR) techniques. African Journal of Biotechnology 2015, 14, 1947 -1953.

AMA Style

Zayed Ehab, Sayed Mervat, Omar Ahmad, Ehab Zayed#, Mervat Sayed, Ahmad Omar#. Genetic variations between two ecotypes of Egyptian clover by inter-simple sequence repeat (ISSR) techniques. African Journal of Biotechnology. 2015; 14 (23):1947-1953.

Chicago/Turabian Style

Zayed Ehab; Sayed Mervat; Omar Ahmad; Ehab Zayed#; Mervat Sayed; Ahmad Omar#. 2015. "Genetic variations between two ecotypes of Egyptian clover by inter-simple sequence repeat (ISSR) techniques." African Journal of Biotechnology 14, no. 23: 1947-1953.

Journal article
Published: 01 March 2011 in Acta Horticulturae
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J.W. Grosser; M. Dutt; A. Omar; V. Orbovic; G. Barthe. PROGRESS TOWARDS THE DEVELOPMENT OF TRANSGENIC DISEASE RESISTANCE IN CITRUS. Acta Horticulturae 2011, 101 -107.

AMA Style

J.W. Grosser, M. Dutt, A. Omar, V. Orbovic, G. Barthe. PROGRESS TOWARDS THE DEVELOPMENT OF TRANSGENIC DISEASE RESISTANCE IN CITRUS. Acta Horticulturae. 2011; (892):101-107.

Chicago/Turabian Style

J.W. Grosser; M. Dutt; A. Omar; V. Orbovic; G. Barthe. 2011. "PROGRESS TOWARDS THE DEVELOPMENT OF TRANSGENIC DISEASE RESISTANCE IN CITRUS." Acta Horticulturae , no. 892: 101-107.

Journal article
Published: 01 September 2009 in Weed Technology
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There is an urgent need to accelerate the development and implementation of effective organic-compliant herbicides that are environmentally safe and that help the producer meet increasing consumer demand for organic products. Therefore, greenhouse experiments were conducted to evaluate the effectiveness of acetic acid (5%), acetic acid (30%), citric acid (10%), citric acid (5%) + garlic (0.2%), citric acid (10%) + garlic (0.2%), clove oil (45.6%), and corn gluten meal (CGM) compounds as natural-product herbicides for weed control. The herbicides were applied to the broadleaf weeds stranglervine, wild mustard, black nightshade, sicklepod, velvetleaf, and redroot pigweed and to narrowleaf weeds crowfootgrass, Johnsongrass, annual ryegrass, goosegrass, green foxtail, and yellow nutsedge. The herbicides were applied POST at two weed growth stages, namely, two to four and four to six true-leaf stages. CGM was applied PPI in two soil types. Citric acid (5%) + garlic (0.2%) had the greatest control (98%) of younger broadleaf weeds, followed by acetic acid (30%) > CGM > citric acid (10%) > acetic acid (5%) > citric acid (10%) + garlic (0.2%), and clove oil. Wild mustard was most sensitive to these herbicides, whereas redroot pigweed was the least sensitive. Herbicides did not control narrowleaf weeds except for acetic acid (30%) when applied early POST (EPOST) and CGM. Acetic acid (30%) was phytotoxic to all broadleaf weeds and most narrowleaf weeds when applied EPOST. Delayed application until the four- to six-leaf stage significantly reduced efficacy; acetic acid was less sensitive to growth stage than other herbicides. These results will help to determine effective natural herbicides for controlling weeds in organic farming.

ACS Style

Hussein F. H. Abouziena; Ahmad A. M. Omar; Shiv D. Sharma; Megh Singh. Efficacy Comparison of Some New Natural-Product Herbicides for Weed Control at Two Growth Stages. Weed Technology 2009, 23, 431 -437.

AMA Style

Hussein F. H. Abouziena, Ahmad A. M. Omar, Shiv D. Sharma, Megh Singh. Efficacy Comparison of Some New Natural-Product Herbicides for Weed Control at Two Growth Stages. Weed Technology. 2009; 23 (3):431-437.

Chicago/Turabian Style

Hussein F. H. Abouziena; Ahmad A. M. Omar; Shiv D. Sharma; Megh Singh. 2009. "Efficacy Comparison of Some New Natural-Product Herbicides for Weed Control at Two Growth Stages." Weed Technology 23, no. 3: 431-437.