Accumulated capsaicinoid content and increased fruit size are traits resulting fromCapsicum annuumdomestication. In this study, we used a diverse collection ofC. annuumto generate 66,960 SNPs using genotyping by sequencing. The study identified 1189 haplotypes containing 3413 SNPs. Length of individual linkage disequilibrium (LD) blocks varied along chromosomes, with regions of high and low LD interspersed with an average LD of 139 kb. Principal component analysis (PCA), Bayesian model based population structure analysis and an Euclidean tree built based on identity by state (IBS) indices revealed that the clustering pattern of diverse accessions are in agreement with capsaicin content (CA) and fruit weight (FW) classifications indicating the importance of these traits in shaping modern pepper genome. PCA and IBS were used in a mixed linear model of capsaicin and dihydrocapsaicin content and fruit weight to reduce spurious associations because of confounding effects of subpopulations in genome-wide association study (GWAS). Our GWAS results showed SNPs in Ankyrin-like protein, IKI3 family protein, ABC transporter G family and pentatricopeptide repeat protein are the major markers for capsaicinoids and of 16 SNPs strongly associated with FW in both years of the study, 7 are located in known fruit weight controlling genes.

A large single nucleotide polymorphism (SNP) dataset was used to analyze genome-wide diversity in a diverse collection of watermelon cultivars representing globally cultivated, watermelon genetic diversity. The marker density required for conducting successful association mapping depends on the extent of linkage disequilibrium (LD) within a population. Use of genotyping by sequencing reveals large numbers of SNPs that in turn generate opportunities in genome-wide association mapping and marker-assisted selection, even in crops such as watermelon for which few genomic resources are available. In this paper, we used genome-wide genetic diversity to study LD, selective sweeps, and pairwise F ST distributions among worldwide cultivated watermelons to track signals of domestication. We examined 183 Citrullus lanatus var. lanatus accessions representing domesticated watermelon and generated a set of 11,485 SNP markers using genotyping by sequencing. With a diverse panel of worldwide cultivated watermelons, we identified a set of 5,254 SNPs with a minor allele frequency of ≥ 0.05, distributed across the genome. All ancestries were traced to Africa and an admixture of various ancestries constituted secondary gene pools across various continents. A sliding window analysis using pairwise F ST values was used to resolve selective sweeps. We identified strong selection on chromosomes 3 and 9 that might have contributed to the domestication process. Pairwise analysis of adjacent SNPs within a chromosome as well as within a haplotype allowed us to estimate genome-wide LD decay. LD was also detected within individual genes on various chromosomes. Principal component and ancestry analyses were used to account for population structure in a genome-wide association study. We further mapped important genes for soluble solid content using a mixed linear model. Information concerning the SNP resources, population structure, and LD developed in this study will help in identifying agronomically important candidate genes from the genomic regions underlying selection and for mapping quantitative trait loci using a genome-wide association study in sweet watermelon.

Melon (Cucumis melo L.) is a phenotypically diverse eudicot diploid (2n = 2x = 24) has climacteric and non-climacteric morphotypes and show wide variation for fruit firmness, an important trait for transportation and shelf life. We generated 13,789 SNP markers using genotyping-by-sequencing (GBS) and anchored them to chromosomes to understand genome-wide fixation indices (Fst) between various melon morphotypes and genomewide linkage disequilibrium (LD) decay. The F_ST between accessions of cantalupensis and inodorus was 0.23. The F_ST between cantalupensis and various agrestis accessions was in a range of 0.19–0.53 and between inodorus and agrestis accessions was in a range of 0.21–0.59 indicating sporadic to wide ranging introgression. The EM (Expectation Maximization) algorithm was used for estimation of 1436 haplotypes. Average genome-wide LD decay for the melon genome was noted to be 9.27 Kb. In the current research, we focused on the genome-wide divergence underlying diverse melon horticultural groups. A high-resolution genetic map with 7153 loci was constructed. Genome-wide segregation distortion and recombination rate across various chromosomes were characterized. Melon has climacteric and non-climacteric morphotypes and wide variation for fruit firmness, a very important trait for transportation and shelf life. Various levels of QTLs were identified with high to moderate stringency and linked to fruit firmness using both genome-wide association study (GWAS) and biparental mapping. Gene annotation revealed some of the SNPs are located in β-D-xylosidase, glyoxysomal malate synthase, chloroplastic anthranilate phosphoribosyltransferase, and histidine kinase, the genes that were previously characterized for fruit ripening and softening in other crops.

Background: Cucumber,Cucumis sativusL. (2n = 2 × = 14) and melon,C. meloL. (2n = 2 × = 24) are two important vegetable species in the genusCucumis(family Cucurbitaceae). Both species have an Asian origin that diverged approximately nine million years ago. Cucumber is believed to have evolved from melon through chromosome fusion, but the details of this process are largely unknown. In this study, comparative genetic mapping between cucumber and melon was conducted to examine syntenic relationships of their chromosomes.Results: Using two melon mapping populations, 154 and 127 cucumber SSR markers were added onto previously reported F₂- and RIL-based genetic maps, respectively. A consensus melon linkage map was developed through map integration, which contained 401 co-dominant markers in 12 linkage groups including 199 markers derived from the cucumber genome. Syntenic relationships between melon and cucumber chromosomes were inferred based on associations between markers on the consensus melon map and cucumber draft genome scaffolds. It was determined that cucumber Chromosome 7 was syntenic to melon Chromosome I. Cucumber Chromosomes 2 and 6 each contained genomic regions that were syntenic with melon chromosomes III+V+XI and III+VIII+XI, respectively. Likewise, cucumber Chromosomes 1, 3, 4, and 5 each was syntenic with genomic regions of two melon chromosomes previously designated as II+XII, IV+VI, VII+VIII, and IX+X, respectively. However, the marker orders in several syntenic blocks on these consensus linkage maps were not co-linear suggesting that more complicated structural changes beyond simple chromosome fusion events have occurred during the evolution of cucumber.Conclusions: Comparative mapping conducted herein supported the hypothesis that cucumber chromosomes may be the result of chromosome fusion from a 24-chromosome progenitor species. Except for a possible inversion, cucumber Chromosome 7 has largely remained intact in the past nine million years since its divergence from melon. Meanwhile, many structural changes may have occurred during the evolution of the remaining six cucumber chromosomes. Further characterization of the genomic nature ofCucumisspecies closely related to cucumber and melon might provide a better understanding of the evolutionary history leading to modern cucumber.

ATP-binding cassette (ABC) transporter genes act as transporters for different molecules across biological membranes and are involved in a diverse range of biological processes. In this study, we performed a genome-wide identification and expression analysis of genes encoding ABC transporter proteins in three Capsicum species, i.e., Capsicum annuum, Capsicum baccatum and Capsicum chinense. Capsicum is a valuable horticultural crop worldwide as an important constituent of many foods while containing several medicinal compounds including capsaicin and dihydrocapsaicin. Our results identified the presence of a total of 200, 185 and 187 ABC transporter genes in C. annuum, C. baccatum and C. chinense genomes, respectively. Capsaicin and dihydrocapsaicin content were determined in green pepper fruits (16 dpa). Additionally, we conducted different bioinformatics analyses including ABC genes classification, gene chromosomal location, Cis elements, conserved motifs identification and gene ontology classification, as well as profile expression of selected genes. Based on phylogenetic analysis and domain organization, the Capsicum ABC gene family was grouped into eight subfamilies. Among them, members within the ABCG, ABCB and ABCC subfamilies were the most abundant, while ABCD and ABCE subfamilies were less abundant throughout all species. ABC members within the same subfamily showed similar motif composition. Furthermore, common cis-elements involved in the transcriptional regulation were also identified in the promoter regions of all Capsicum ABC genes. Gene expression data from RNAseq and reverse transcription-semi-quantitative PCR analysis revealed development-specific stage expression profiles in placenta tissues. It suggests that ABC transporters, specifically the ABCC and ABCG subfamilies, may be playing important roles in the transport of secondary metabolites such as capsaicin and dihydrocapsaicin to the placenta vacuoles, effecting on their content in pepper fruits. Our results provide a more comprehensive understanding of ABC transporter gene family in different Capsicum species while allowing the identification of important candidate genes related to capsaicin content for subsequent functional validation.

MicroRNAs (miRNAs), a class of small non-coding endogenous RNAs that regulate gene expression post-transcriptionally, play multiple key roles in plant growth and development and in biotic and abiotic stress response. Knowledge and roles of miRNAs in pomegranate fruit development have not been explored. Pomegranate, which accumulates a large amount of anthocyanins in skin and arils, is valuable to human health, mainly because of its antioxidant properties. In this study, we developed a small RNA library from pooled RNA samples from young seedlings to mature fruits and identified both conserved and pomegranate-specific miRNA from 29,948,480 high-quality reads. For the pool of 15- to 30-nt small RNAs, ~50 % were 24 nt. The miR157 family was the most abundant, followed by miR156, miR166, and miR168, with variants within each family. The base bias at the first position from the 5’ end had a strong preference for U for most 18- to 26-nt sRNAs but a preference for A for 18-nt sRNAs. In addition, for all 24-nt sRNAs, the nucleotide U was preferred (97 %) in the first position. Stem-loop RT-qPCR was used to validate the expression of the predominant miRNAs and novel miRNAs in leaves, male and female flowers, and multiple fruit developmental stages; miR156, miR156a, miR159a, miR159b, and miR319b were upregulated during the later stages of fruit development. Higher expression of miR156 in later fruit developmental may positively regulate anthocyanin biosynthesis by reducing SPL transcription factor. Novel miRNAs showed variation in expression among different tissues. These novel miRNAs targeted different transcription factors and hormone related regulators. Gene ontology and KEGG pathway analyses revealed predominant metabolic processes and catalytic activities, important for fruit development. In addition, KEGG pathway analyses revealed the involvement of miRNAs in ascorbate and linolenic acid, starch and sucrose metabolism; RNA transport; plant hormone signaling pathways; and circadian clock. Our first and preliminary report of miRNAs will provide information on the synthesis of biochemical compounds of pomegranate for future research. The functions of the targets of the novel miRNAs need further investigation.