Background: De novo assembly of transcript sequences produced by next-generation sequencing technologies offers a rapid approach to obtain expressed gene sequences for non-model organisms. Ammopiptanthus mongolicus, a super-xerophytic broadleaf evergreen wood, is an ecologically important foundation species in desert ecosystems and exhibits substantial drought tolerance in Mid-Asia desert. Root plays an important role in water absorption of plant. There are insufficient transcriptomic and genomic data in public databases for understanding of the molecular mechanism underlying the drought tolerance of A. mongolicus. Thus, high throughput transcriptome sequencing from A. mongolicus root is helpful to generate a large amount of transcript sequences for gene discovery and molecular marker development. Results: A total of 672,002 sequencing reads were obtained from a 454 GS XLR70 Titanium pyrosequencer with a mean length of 279 bp. These reads were assembled into 29,056 unique sequences including 15,173 contigs and 13,883 singlets. In our assembled sequences, 1,827 potential simple sequence repeats (SSR) molecular markers were discovered. Based on sequence similarity with known plant proteins, the assembled sequences represent approximately 9,771 proteins in PlantGDB. Based on the Gene ontology (GO) analysis, hundreds of drought stress-related genes were found. We further analyzed the gene expression profiles of 27 putative genes involved in drought tolerance using quantitative real-time PCR (qRT-PCR) assay. Conclusions: Our sequence collection represents a major transcriptomic resource for A. mongolicus, and the large number of genetic markers predicted should contribute to future research in Ammopiptanthus genus. The potential drought stress related transcripts identified in this study provide a good start for further investigation into the drought adaptation in Ammopiptanthus.

Astragalus membranaceus is an important medicinal plant widely cultivated in East Asia. MicroRNAs (miRNAs) are endogenous regulatory molecules that play essential roles in plant growth, development, and the response to environmental stresses. Cold is one of the key environmental factors affecting the yield and quality of A. membranaceus, and miRNAs may mediate the gene regulation network under cold stress in A. membranaceus. To identify miRNAs and reveal their functions in cold stress response in A. membranaceus, small RNA sequencing was conducted followed by bioinformatics analysis, and quantitative real time PCR (qRT-PCR) analysis was performed to profile the expression of miRNAs under cold stress. A total of 168 conserved miRNAs belonging to 34 families and 14 putative non-conserved miRNAs were identified. Many miRNA targets were predicted and these targets were involved in diversified regulatory and metabolic pathways. By using qRT-PCR, 27 miRNAs were found to be responsive to cold stress, including 4 cold stress-induced and 17 cold-repressed conserved miRNAs, and 6 cold-induced non-conserved miRNAs. These cold-responsive miRNAs probably mediate the response to cold stress by regulating development, hormone signaling, defense, redox homeostasis, and secondary metabolism in A. membranaceus. These cold-corresponsive miRNAs may be used as the candidate genes in further molecular breeding for improving cold tolerance of A. membranaceus.

Plasma membrane intrinsic proteins (PIPs) are a subfamily of aquaporin proteins located on plasma membranes where they facilitate the transport of water and small uncharged solutes. PIPs play an important role throughout plant development, and in response to abiotic stresses. Jojoba (Simmondsia chinensis (Link) Schneider), as a typical desert plant, tolerates drought, salinity and nutrient-poor soils. In this study, a PIP1 gene (ScPIP1) was cloned from jojoba and overexpressed in Arabidopsis thaliana. The expression of ScPIP1 at the transcriptional level was induced by polyethylene glycol (PEG) treatment. ScPIP1 overexpressed Arabidopsis plants exhibited higher germination rates, longer roots and higher survival rates compared to the wild-type plants under drought and salt stresses. The results of malonaldehyde (MDA), ion leakage (IL) and proline content measurements indicated that the improved drought and salt tolerance conferred by ScPIP1 was correlated with decreased membrane damage and improved osmotic adjustment. We assume that ScPIP1 may be applied to genetic engineering to improve plant tolerance based on the resistance effect in transgenic Arabidopsis overexpressing ScPIP1.

Soil contamination by chromium (Cr) has become an increasing problem worldwide as a result of extensive industrial activities. Chromium, especially hexavalent Cr, impairs the growth and productivity of plants. Although it has been proposed that plants could modify their metabolism to adapt to Cr stress by reprogramming the expression of genes, especially those related to the antioxidant system, damage response, and electron transport chain, evidence at the protein expression level is lacking. To better understand the precise mechanisms underlying Cr phytoxicity and the plant response to Cr exposure, the time-course of changes in the protein expression profile induced by short-term hexavalent Cr exposure (1, 6 and 24 h) were analyzed in maize leaves. Among the over 1200 protein spots detected reproducibly by two-dimensional electrophoresis (2-DE), 60 were found to be differentially accumulated during Cr stress treatment. Of the Cr-regulated proteins, 58 were identified using tandem mass spectrometry (MS/MS). The Cr-regulated proteins identified were mainly involved in ROS detoxification and defense responses (26%), photosynthesis and chloroplast organization (22%), post-transcriptional processing of mRNA and rRNA (12%), protein synthesis and folding (10%), the DNA damage response (5%), and the cytoskeleton (3%). The possible involvement of these Cr stress-responsive proteins in Cr phytoxicity and the plant response to Cr exposure in maize is discussed, taking into consideration the information available from other plant models. Our results provide preliminary evidence that will facilitate understanding the molecular mechanisms underlying Cr toxicity in maize.

Glutathione peroxidases (GPX) catalyze the reduction of H₂O₂ or organic hydroperoxides to water or corresponding alcohols using reduced glutathione, which plays an essential role in ROS (reactive oxygen species) homeostasis and stress signaling. Thellungiella salsuginea (Eutrema salsugineum), a relative of Arabidopsis thaliana, displays an extremely high level of tolerance to salt, drought, cold and oxidative stresses. The enzymatic antioxidant systems may contribute to the stress tolerance of T. salsuginea. In the present study, we aimed at understanding the roles of the antioxidant enzymes in T. salsuginea by focusing on the GPX family. We identified the eight GPX genes in T. salsuginea, and the structure of the N-terminal domains indicated their putative chloroplastic, mitochondrial and cytoplasmic location. The exon-intron organization of these genes exhibited a conserved pattern among plant GPX genes. Multiple environmental stresses and hormone response related cis-acting elements were predicted in the promoters of TsGPX genes. The gene and protein expression profiles of TsGPXs in response to high level of salinity and osmotic stresses, in leaves and roots of T. salsuginea were investigated using real-time RT-PCR and western blotting analysis. Our result showed that different members of the GPX gene family were coordinately regulated under specific environmental stress conditions, and supported the important roles of TsGPXs in salt and drought stress response in T. salsuginea.

APETALA2/ethylene-responsive factor (AP2/ERF) is one of the largest transcription factor (TF) families in plants, which play important roles in regulating plant growth, development, and response to environmental stresses. Ammopiptanthus nanus, an unusual evergreen broad-leaved shrub in the arid region in the northern temperate zone, demonstrates a strong tolerance to low temperature and drought stresses, and AP2/ERF transcription factors may contribute to the stress tolerance of A. nanus. In the current study, 174 AP2/ERF family members were identified from the A. nanus genome, and they were divided into five subfamilies, including 92 ERF members, 55 dehydration-responsive element binding (DREB) members, 24 AP2 members, 2 RAV members, and 1 Soloist member. Compared with the other leguminous plants, A. nanus has more members of the DREB subfamily and the B1 group of the ERF subfamily, and gene expansion in the AP2/ERF family is primarily driven by tandem and segmental duplications. Promoter analysis showed that many stress-related cis-acting elements existed in promoter regions of the DREB genes, implying that MYB, ICE1, and WRKY transcription factors regulate the expression of DREB genes in A. nanus. Expression profiling revealed that the majority of DREB members were responsive to osmotic and cold stresses, and several DREB genes such as EVM0023336.1 and EVM0013392.1 were highly induced by cold stress, which may play important roles in cold response in A. nanus. This study provided important data for understanding the evolution and functions of AP2/ERF and DREB transcription factors in A. nanus.