Piriformospora indica confers drought tolerance on Zea mays L.through enhancement of antioxidant activity and expression of drought-related genes

Drought stress is one of the most severe environmental constraints to plant growth and crop productivity. Plant growth is greatly affected by drought stress, and plants, to survive,adapt to this stress by invoking different pathways. Piriformospora indica, a root-colonizing endophytic fungus of Sebacinales, promotes plant growth and confers resistance to biotic and abiotic stresses, including drought stress, by affecting the physiological properties of the host plant. The fungus strongly colonizes the roots of maize(Zea mays L.) and promotes shoot and root growth under both normal growth conditions and drought stress. We used polyethylene glycol(PEG-6000) to mimic drought stress and found that root fresh and dry weight, leaf area, SPAD value, and leaf number were increased in P. indica-colonized plants.The antioxidative activities of catalases and superoxide dismutases were upregulated within 24h in the leaves of P. indica-colonized plants. Drought-related genes DREB2A, CBL1,ANAC072, and RD29A were upregulated in drought-stressed leaves of P. indica-colonized plants. Furthermore, after drought treatment, proline content increased, whereas accumulation of malondialdehyde(MDA), an indicator of membrane damage, decreased in P. indica-colonized maize. We conclude that P. indica-mediated plant protection against the detrimental effects of drought may result from enhanced antioxidant enzyme activity,proline accumulation, and expression of drought-related genes and lower membrane damage in maize plants.

Overexpression of the Suaeda salsa SsNHX1 gene confers enhanced salt and drought tolerance to transgenic Zea mays

Maize is one of the most important crops worldwide, but it suffers from salt stress when grown in saline-alkaline soil. There is therefore an urgent need to improve maize salt tolerance and crop yield. In this study, the SsNHX1 gene of Suaeda salsa, which encodes a vacuolar membrane Na~+/H~+ antiporter, was transformed into the maize inbred line 18-599 by Agrobacterium-mediated transformation. Transgenic maize plants overexpressing the SsNHX1 gene showed less growth retardation when treated with an increasing NaCl gradient of up to 1%, indicating enhanced salt tolerance. The improved salt tolerance of transgenic plants was also demonstrated by a significantly elevated seed germination rate(79%) and a reduction in seminal root length inhibition. Moreover, transgenic plants under salt stress exhibited less physiological damage. SsNHX1-overexpressing transgenic maize accumulated more Na~+ and K~+ than wild-type(WT) plants particularly in the leaves, resulting in a higher ratio of K~+/Na~+ in the leaves under salt stress. This result revealed that the improved salt tolerance of SsNHX1-overexpressing transgenic maize plants was likely attributed to SsNHX1-mediated localization of Na~+ to vacuoles and subsequent maintenance of the cytosolic ionic balance. In addition, SsNHX1 overexpression also improved the drought tolerance of the transgenic maize plants, as rehydrated transgenic plants were restored to normal growth while WT plants did not grow normally after dehydration treatment. Therefore, based on our engineering approach, SsNHX1 represents a promising candidate gene for improving the salt and drought tolerance of maize and other crops.

Genome-wide identification and comparative analysis of drought related genes in roots of two maize inbred lines with contrasting drought tolerance by RNA sequencing

Drought is one of the most important abiotic stresses affecting maize growth and development and therefore resulting in yield loss.Thus it is essential to understand molecular mechanisms of drought stress responses in maize for drought tolerance improvement.The root plays a critical role in plants sensing water deficit.In the present study,two maize inbred lines,H082183,a drought-tolerant line,and Lv28,a drought-sensitive line,were grown in the field and treated with different water conditions(moderate drought,severe drought,and well-watered conditions)during vegetative stage.The transcriptomes of their roots were investigated by RNA sequencing.There were 1428 and 512 drought-responsive genes(DRGs)in Lv28,688 and 3363 DRGs in H082183 under moderate drought and severe drought,respectively.A total of 31 Gene Ontology(GO)terms were significantly over-represented in the two lines,13 of which were enriched only in the DRGs of H082183.Based on results of Kyoto encyclopedia of genes and genomes(KEGG)enrichment analysis,"plant hormone signal transduction"and"starch and sucrose metabolism"were enriched in both of the two lines,while"phenylpropanoid biosynthesis"was only enriched in H082183.Further analysis revealed the different expression patterns of genes related to abscisic acid(ABA)signal pathway,trehalose biosynthesis,reactive oxygen scavenging,and transcription factors might contribute to drought tolerance in maize.Our results contribute to illustrating drought-responsive molecular mechanisms and providing gene resources for maize drought improvement.

Analysis of drought resistance HVA1 gene under drought stress in different Poa pratensis cultivars

Total RNA from leaves of Poapratensis cultivars under drought stress was extracted for reversing transcription to cDNA and then cDNA as template for PCR reaction by designing primer of cds of Hordeum valgare HVA1 drought resistance gene from GenBank. The amplified products were positive recon identified by using procedures of recovery, connection, transformation and enzyme separation. The length of cloned gene sequence was 324 bp, identity reached 79.27% with Barley HVA1 gene that meaned the cloned gene sequence was the partial HVA1 gene of Poapratensis.

Downregulation of SL-ZH13 transcription factor gene expression decreases drought tolerance of tomato

Zinc finger-homeodomain proteins(ZF-HDs) are transcription factors that regulate plant growth,development,and abiotic stress tolerance.The SL-ZH13 gene was found to be significantly upregulated under drought stress treatment in tomato(Solanum lycopersicum) leaves in our previous study.In this study,to further understand the role that the SL-ZH13 gene plays in the response of tomato plants to drought stress,the virus-induced gene silencing(VIGS) method was applied to downregulate SL-ZH13 expression in tomato plants,and these plants were treated with drought stress to analyze the changes in drought tolerance.The SL-ZH13 silencing efficiency was confirmed by quantitative real-time PCR(qRT-PCR) analysis.In SL-ZH13-silenced plants,the stems wilted faster,leaf shrinkage was more severe than in control plants under the same drought stress treatment conditions,and the mean stem bending angle of SL-ZH13-silenced plants was smaller than that of control plants.Physiological analyses showed that the activity of superoxide dismutase(SOD) and peroxidase(POD) and the content of proline(Pro) in SL-ZH13-silenced plants were lower than those in control plants after 1.5 and 3 h of drought stress treatment.The malondialdehyde(MDA) content in SL-ZH13-silenced plants was higher than that in control plants after 1.5 and 3 h of drought stress treatment,and H2O2 and O2^-· accumulated much more in the leaves of SL-ZH13-silenced plants than in the leaves of control plants.These results suggested that silencing the SL-ZH13 gene affected the response of tomato plants to drought stress and decreased the drought tolerance of tomato plants.

Reference genes for quantitative real-time PCR analysis and quantitative expression of P5CS in Agropyron mongolicum under drought stress

Reference genes, stably expressing in different tissues and cells, are commonly used as the references in expression analysis. Selecting the optimum reference gene is crucial to the success of experiments. In this study, the expression stabilities of nine common reference genes, including ACT2, 18 S r RNA, APRT, EF-1α, RNA POL II, TUBα, TUBβ, GAPDH and TLF of Agropyron mongolicum, were studied under drought condition. Among them, 18 S r RNA was found to be the most optimum reference gene under drought stress by the analyzing of ge Norm and Norm Finder software. Quantitative expression levels of P5 CS using 18 S r RNA as the reference gene, and proline contents under drought stress in A. mongolicum were further operated, and we found the expression level of P5 CS gene and proline content had a significantly positive relationship（R^2=0.7763, P〈0.05）. This study established and validated 18 S r RNA as the reference genes in A. mongolicum under drought stress, providing a powerful tool for the quantitative expression analysis of drought genes in A. mongolicum.

Biotic and abiotic stress-responsive genes are stimulated to resist drought stress in purple wheat

Triticum aestivum L. cv. Guizi 1(GZ1) is a drought-tolerant local purple wheat cultivar. It is not clear how purple wheat resists drought stress, but it could be related to anthocyanin biosynthesis. In this study, transcriptome data from droughttreated samples and controls were compared. Drought slightly reduced the anthocyanin, protein and starch contents of GZ1 grains and significantly reduced the grain weight. Under drought stress, 16 682 transcripts were reduced, 27 766 differentially expressed genes(DEGs) were identified, and 379 DEGs, including DREBs, were related to defense response. The defense-response genes included response to water deprivation, reactive oxygen, bacteria, fungi, etc. Most of the structural and regulatory genes in anthocyanin biosynthesis were downregulated, with only Ta DFR, Ta OMT, Ta5,3GT, and Ta MYB-4 B1 being upregulated. Ta CHS, Ta F3H, TaCHI, Ta4CL, and TaF3’H are involved in responses to UV, hormones, and stimulus. Ta CHS-2D1, Ta DFR-2D2, Ta DFR-7D, TaOMT-5A, Ta5,3 GT-1B1, Ta5,3GT-3A, and Ta5,3GT-7B1 connect anthocyanin biosynthesis with other pathways, and their interacting proteins are involved in primary metabolism, genetic regulation, growth and development, and defense responses. There is further speculation about the defense-responsive network in purple wheat. The results indicated that biotic and abiotic stress-responsive genes were stimulated to resist drought stress in purple wheat GZ1, and anthocyanin biosynthesis also participated in the drought defense response through several structural genes.

Cloning of the OAT gene and the correlation between its expression and drought tolerance in Phaseolus vulgaris L.

Drought stress is a major abiotic stress of common bean（Phaseolus vulgaris L.） throughout the world. Increasing the proline accumulation contributes to enhance crop drought tolerance. A c DNA for δ-o rnithine aminotransferase（δ-OAT）, an enzyme involved in the biosynthesis of proline, was isolated from Phaseolus vulgaris（Pv OAT）. Pv OAT exhibits 87.4 and 39.8% similarity of the deduced amino acid sequences with δ-OAT from Glycine max and Vigna aconitifolia, respectively. The transcriptional analysis revealed that Pv OAT was strongly induced by drought stress. And the expression of Pv OAT was higher in leaves than that in the root and stem of common bean by drought stress. Similar increase of the proline accumulation was observed in leaves and roots of common bean by drought stress. Furthermore, the proline content, the Pv OAT expression and the Pv OAT enzyme activity in cul tivar F5575 was significantly（P〈0.01） higher than that in cultivar F4851 under drought-stress conditions. Interestingly, it had been observed that, in the later stage of drought stress, the proline steadily maintained at the maximum level maybe result from the Pv OAT enzyme activity increasing steadily. These r esults indicated that the expression of Pv OAT and the accumulation of proline induced by drought stress treatment were related to the degree of common bean drought tolerance. So our results support the view that δ-OAT is associated with proline synthesis under drought stress conditions.

Cloning and Expression Analysis of OsNADPH1 Gene from Rice in Drought Stress Response

An experiment was conducted to compare the mRNA expression difference in rice leaves and roots under drought stress and normal conditions us, ng Fluorescent Differential Display （FDD） method. One positive fragment was isolated by combination of the H. A. Yellow-PAGE （cont,~ined 0.1% H. A. Yellow） separation and macroarray screening methods. Compared to Arabidopsis thaliana NADPH oxidoreductase gene, it has 96% identity. The cDNA was 1423 bp, and contained a complete open reading frame of 1048 bp encoding a protein with 345 amino acid residues. Moreover, the gene expression level was higher under drought stress than that under normal conditions. The possible role of NADPH oxidoreductase gene under drought response was also discussed.

Down-Regulated Expression of RACK1 Gene by RNA Interference Enhances Drought Tolerance in Rice

The receptor for activated C-kinase 1 （RACK1） is a highly conserved scaffold protein with versatile functions, and plays important roles in the regulation of plant growth and development. Transgenic rice plants, in which the expression of RACK1 gene was inhibited by RNA interference （RNAi）, were studied to elucidate the possible functions of RACK1 in responses to drought stress in rice. Real-time PCR analysis showed that the expression of RACK1 in transgenic rice plants was inhibited by more than 50%. The tolerance to drought stress of the transgenic rice plants was higher as compared with the non-transgenic rice plants. The peroxidation of membrane and the production of malondialdehyde were significantly lower and the superoxide dismutase activity in transgenic rice plants was significantly higher than those in non-trangenic rice plants It is suggested that RACK1 negatively regulated the redox system-related tolerance to drought stress of rice plants.

Role of LOX3 Gene in Alleviating Adverse Effects of Drought and Pathogens in Rice

Lipoxygenase 3 (LOX3) is a major component of the LOX isozymes in mature rice seeds. To investigate the role of LOX3 gene under stresses, a plant expression vector containing antisense cDNA of LOX3 was constructed. Rice varieties Wuyunjing 7 and Kasalath were transformed by the Agrobacterium-mediated method and transgenic rice plants were generated. PCR and Southern blot results showed that the antisense LOX3 gene was integrated into the rice genome. Analyses of embryo LOX3 deletion and semi-quantitative RT-PCR confirmed the antisense suppression of LOX3 gene in transgenic plants. The T2 antisense plants of LOX3 were sensitive to drought stress, rice blast and bacterial blight compared with non-transgenic plants. These results suggest that the LOX3 gene might function in response to stresses.

Active Methyl Cycle and Transfer Related Gene Expression in Response to Drought Stress in Rice Leaves

Three rice varieties, Zhonghan 3, Shanyou 63 and Aizizhan, were used as materials in detecting differential active methyl cycle and transfer related gene expression in response to drought stress. The experiment was performed by gene chip and mRNA differential display technologies under the conditions of drought simulated with 10% PEG6000 solution. The results indicated that the methyl cycle could be activated in the leaves of Zhonghan 3 and Shanyou 63 but inhibited in the leaves of Aizizhan under drought stress. Furthermore, drought stress could induce the expression of a large number of methyltransferase genes, especially the transcription of Rubisco protein methylation related genes, which are beneficial for prevention of Rubisco protein oxidation and degradation, and drought stress could inhibit the transcription of DNA methyltransferase genes and histone methyltransferase genes. This result confirmed that the active methyl cycle and transfer related genes were involved in rice drought resistance.

Identification and characterization drought tolerance of gene <i>LEA-D</i>11 soybean (<i>glycine max</i>L. Merr) based on PCR-sequencing

Drought is one of the most damaging abiotic stress. Different plants response differently to drought stress. Abiotic stresses such as drought induced diverse physicological and molecular responses in plants. These responses include changes in gene expression. One of drought tolerance gene is a gene encoding dehydrin which is belongs to the group II or D-11 LEA protein family. LEA-D11 gene produce dehydrin protein which has a role in stabilization of membrane structures and protection of macromolecules in the presence of drought. The aims of the study was to identify and to characterize the LEA-D11 gene in various soybean varieties. This research used seven varieties of soybean: Tanggamus, Nanti, Seulawah, Tidar (drought tolerant), Wilis and Burangrang (drought moderate) and Detam-1 (drought susceptible). DNA genome of those varieties was isolated using the methods from Doyle & Doyle [1]. DNA amplification was conducted using Polymerase Chain Reaction (PCR) with specific primers designed based on GmLEA-D11 gene sequence database from the NCBI. The DNA targets were sequenced using automatic sequencing machine, ABI 3130xl Genetic Analyzer, in Eijkman Institution. The result of this study showed that the sequences of Gm-LEA-D11 gene possessed by drought tolerance varieties (Tanggamus, Nanti, Seulawah and Tidar) and moderately tolerance (Wilis and Burangrang) were similar. However, the sequence of GmLEA-D11 gene detected in the drought susceptible variety Detam-1 was different from the two groups. Similarity between drought tolerance and moderately tolerance indicate that there is not only LEA-D11 gene responsible to drought tolerance but also others. The primer and sequences GmLEA-D11 gene can be used as molecular marker and capable of differentiating between drought susceptible and drought moderate to drought tolerant.

Responses of Drought-Resistant Mutant vem1 to Stress and Cloning of VEM1 Gene in Arabidopsis

[ Objective] This study aimed to investigate the responses of drought-resistant mutant veml to stress and clone VEM1 gene in Arabidopsis. [ Method] A drought-resistant mutant veml was isolated from the Arabidops/s mutant pool. The germination rates of wild-type （WT） and mutant veml were detected to investigate the responses of mutant veml to mannitol, NaCl and ABA stress. [ Result] The mutant veml was resistant to mannitol and NaC1 stress but sensitive to ABA stress. VEM1 gene was cloned by Tail-PCR technology and sequenced. The sequencing result was submitted to NCBI for sequence alignment and gene mapping using BLAST. Database analysis suggested that VEM1 gene was a transposable clement gene. [ Conclusion] This study laid the foundation for functional analysis of drought-resistant gene VEM1.

Drought-responsive genes expressed predominantly in root tissues are enriched with homotypic cis-regulatory clusters in promoters of major cereal crops

The root appears to be the most relevant organ for breeding drought stress tolerance.However, our knowledge about temporal and spatial regulation of drought-associated genes in the root remains fragmented, especially in crop plants. We performed a meta-analysis of expression divergence of essential drought-inducible genes and analyzed their association with cis-elements in model crops and major cereal crops. Our analysis of42 selected drought-inducible genes revealed that these are expressed primarily in roots,followed by shoot, leaf, and inflorescence tissues, especially in wheat. Quantitative real-time RT-PCR analysis confirmed higher expression of TaDREB2 and TaAQP7 in roots,correlated with extensive rooting and drought-stress tolerance in wheat. A promoter scan up to 2 kb upstream of the translation start site using phylogenetic footprinting revealed708 transcription factor binding sites, including drought response elements(DREs), auxin response elements(Aux REs), MYCREs/MYBREs, ABAREs, and ERD1 in 19 selected genes.Interestingly, these elements were organized into clusters of overlapping transcription factor binding sites known as homotypic clusters(HCTs), which modulate drought physiology in plants. Taken together, these results revealed the expression preeminence of major drought-inducible genes in the root, suggesting its crucial role in drought adaptation. The occurrence of HCTs in drought-inducible genes highlights the putative evolutionary modifications of crop plants in developing drought adaptation. We propose that these DNA motifs can be used as molecular markers for breeding drought-resilient cultivars, particularly in the cereal crops.

Isolation of a Plasmalemma Aquaporin Encoding Gene StPIP1 from Solanum tuberosum L. and Its Expression in Transgenic Tobacco

Aquaporin （AQP） belongs to a highly conserved group of membrane proteins considered as major intrinsic proteins, which facilitate water transport across biological membranes. The discovery of AQPs in plants has resulted in a paradigm shift in the understanding of plant-water relations, however, the potential relationship between the role of aquaporins in regulating plant water balance and drought tolerance still remains elusive. In this study, the gene encoding potato AQP cDNA, StPIP1 （GenBank accession no. DQ999080）, was cloned from the leaf of potato cultivar Gannongshu 2 by reverse transcription-PCR （RT-PCR）. Sequence alignment was made by BLASTn in GenBank, the phylogenetic analysis was conducted using PHYLIPWY, the 3D structure was predicted in Swiss-Model server. Subcellular localization of StPIP1 was performed by constructing CaMV35S-StPIP1-GFP and rd29A-StPIP1-GFP fusion proteins and transient expression in onion epidermis. To understand StPIP1 physiological functions in potato under various stress conditions, the StPIP1 gene in a reverse orientation was transformed into tobacco driven by the Cauliflower mosaic virus （CMV） 35S promoter. The expression levels of transgenic and wild-type plants were assessed under various abiotic stress conditions using semi-quantitative RT-PCR, and the morphological and physiological responses of transgenic plants to different stress conditions were investigated. The expression of StPIP1 mRNA decreased in transgenic plants under non-stress and stress conditions, however, the reduction was more severer under drought stress. In both non-stress and stress conditions, StPIP1 was expressed predominantly in root. The morphological and physiological investigation showed no significant differences in growth rate, germination rate, and root fresh weight （FW） between transgenic and wild-type plants when grown under favorable conditions. In contrast, under drought stress, the reduction in StPIPI expression leads to a delay in seed germination and seedling growth, accelerated seedling wilt, and leaf morphological abnormity. Under ＂enough＂ water conditions （i.e., water culture）, the aerial parts of anti-sense plants showed no differences. However, for the aerial parts to accumulate the same amount of biomass, transgenic plants needed about 3 times more abundant root system to transport water for plant growth than wild-type plants. Morphological investigation showed that the reduction in StPIP1 expression increased the root system in transgenic plants under drought stress. As a result, the increase of root mass might compensate the reduced cellular water permeability in order to ensure a sufficient water supply for the plant. Results demonstrated that StPIP1 plays an important role for water transportation in potato, especially under drought stress conditions. The reduced expression of StPIP1 decreases the cellular water transport and influences the expression of endogenous AQPs genes and thereby, has impacts on seed germination, seedling growth, and stress responses of potato to drought conditions.

Wild Barley,Hordeum spontaneum,a Genetic Resource for Crop Improvement in Cold and Arid Regions

Food security in cold and arid regions in the world is threatened by stressful and unpredictable environments.The sus-tainable and economically viable solution for increasing stability of food productivity in cold and arid regions is genetic improvement of crops towards high resistance to abiotic stresses,mainly cold and drought resistance.It is often empha-sized that crop genetic improvement lies in exploiting the gene pools of the wild relatives of the crop plant.Wild barley,H.spontaneum,the progenitor of cultivated barley,is a selfing annual grass of predominantly Mediterranean and Irano-Turanian distribution that penetrates into desert environments where it maintains stable populations.Wild barley is also found in cold regions,such as in Tibet.The adaptation of wild barley to the arid region in Israel and Jordan,and the cold region in Tibet has accumulated rich genetic diversities for drought,salt,and cold resistances in wild barley,which is the genetic resource for barley and other crop improvement in arid and cold regions.These genetic diversities are revealed by allozymes,DNA-based molecular markers,and morphological and physiological traits of wild barley plants.Quantita-tive trait loci(QTLs) related to drought resistance were identified in wild barley via the QTL mapping approach.Drought resistance genes such as dehydrins,hsdr4,and eibi1 were identified in wild barley based on the candidate gene approach,gene differential expression approach,and molecular genetic approach,respectively.Genetics and genomics of wild bar-ley cold resistance have not been exploited yet,remaining a huge treasure for future crop improvement of cold resistance.Advanced backcross QTL analysis,the introgression libraries based on wild barley as donors,a QTL approach based on wide crosses using wild barley,and positional cloning of natural QTLs will play prevailing roles to help us understand the molecular control of cold and drought tolerance.Integration of QTL information into a breeding pipeline aimed at im-proving tolerance to cold and drought will be achieved within a multidisciplinary context.

Molecular analysis of the chloroplast Cu/Zn-SOD gene(AhCSD2) in peanut

Superoxide dismutase(SOD, EC 1.15.1.1) plays a key role in response to drought stress, and differences in SOD activity changes among cultivars are important under drought conditions. We obtained the full-length DNA of the chloroplast Cu/Zn-SOD gene(Ah CSD2)from 11 allotetraploid cultivars and 5 diploid wild species in peanut. BLAST search against the peanut genome showed that the Ah CSD2 genes g CSD2-1 and g CSD2-2 are located at the tops of chromosome A03(A genome) and B03(B genome), respectively, and both contain 8exons and 7 introns. Nucleotide sequence analyses indicated that g CSD2-2 sequences were identical among all the tested cultivars, while g CSD2-1 sequences showed allelic variations.The amino acid sequences deduced from g CSD2-1 and g CSD2-2 both contain a chloroplast transit peptide and are distinguished by 6 amino acid(aa) residue differences. The other 2aa residue variations in the mature peptide regions give rise to three-dimensional structure changes of the protein deduced from the genes g CSD2-1 and g CSD2-2. Sequences analyses of cultivars and wild species showed that g CSD2-2 of Arachis hypogaea and g Aip CSD2(Arachis ipaensis) are identical, and despite the abundant polymorphic loci between g CSD2-1 of A.hypogaea and sequences from A genome wild species, the deduced amino acid sequence of Ah CSD2-1(A. hypogaea) is identical to that of Adu CSD2(Arachis duranensis), whereas Aco CSD2(Arachis correntina) and Aca CSD2(Arachis cardenasii) both have 2 aa differences in the transit peptide region compared with Ah CSD2-1(A. hypogaea). Based on the Peanut Genome Project, promoter prediction revealed many stress-related cis-acting elements within the potential promoter regions(pp-A and pp-B). pp-A contains more binding sites for drought-associated transcriptional factors than pp-B. We hypothesize that the marked changes in SOD activity in different cultivars under drought stress are tightly regulated by transcription factors through transcription and expression of Ah CSD2 genes.

Differential Expression of MicroRNAs in Response to Drought Stress in Maize

Drought is one of the major abiotic stresses that limit maize productivity. Apart from the principal transcriptional regulation, post-transcriptional regulation mediated by microRNAs appears to be the prevalent response of plants to abiotic stress. In this study, the differential expression of microRNAs in the previously evaluated drought-tolerant inbred lines R09 under drought stress was detected by microarray hybridization. The target genes of the differentially-expressed microRNAs were predicted by bioinformatics software WMD3 for plant target gene prediction. The possible regulation of the differentially-expressed microRNAs as well as their target genes in maize response to drought stress was analysed according to Gene Ontology. Sixty-eight microRNAs in 29 microRNA families were detected to be differentially expressed in the seedling of the drought-tolerant inbred line R09, accounting for 5.97% of the total number of the probes. The expression profiles were different between the two time points of the drought stress. The functions of the genes targeted by the differentially-expressed microRNAs involve multiple physiological and biochemical pathways of response to abiotic stress, such as transcription regulation, metabolism, signal transduction, hormone stimulation, and transmembrane transport. Under drought stress, the differential expression of microRNAs regulates the expression of their target genes, resulting in multiple responses of physiological and biochemical pathways relative to drought tolerance of maize, miR156, miR159 and miR319 families may play more important roles. The different members of the same family may play similar regulation effects in most cases.

<i>Arabidopsis</i>Transcription Factor WRKY33 Is Involved in Drought by Directly Regulating the Expression of <i>CesA8</i>

Arabidopsis (Arabidopsis thaliana) WRKY33 is a key transcription factor in pathogen-induced defense signaling, but its function in abiotic stresses remains largely unclear. In this study, we report on the use of a reverse-genetic approach, as well as a yeast (Saccharomyces cerevisiae) expression system, to determine the role of WRKY33 in drought. A T-DNA insertion deletion mutant of WRKY33 is more sensitive to dehydration. Through genome-wide screening the target genes of WRKY33 in yeast, we identified 23 candidate genes including a drought tolerance gene CesA8. Further results revealed that WRKY33 repressed CesA8 expression through binding to the W-box elements of CesA8 distal promoter region and probably interacting with the transcriptional activator of CesA8, MYB46. These findings revealed the primary molecular mechanism underlying the function of WRKY33 in response to