Over-expression of a LEA gene in rice improves drought resistance under the field conditions

Functional characterization of late embryogenesis abundant genes and promoters in pearl millet (Pennisetum glaucum L.) for abiotic stress tolerance

Late embryogenesis abundant (LEA) genes display distinct functions in response to abiotic stresses in plants. In pearl millet (Pennisetum glaucum L.), a total of 21 PgLEA genes were identified and classified into six groups including LEA1, LEA2, LEA3, LEA5, LEA7, and dehydrins (DHN). Open reading frames (ORFs) of PgLEAs range from 291 bp (PgLEA1-1) to 945 bp (PgLEA2-11) and distributed randomly among the seven chromosomes. Phylogenetic analysis revealed that all PgLEA proteins are closely related to sorghum LEA proteins. The PgLEAs were found to be expressed differentially under high progressive vapor pressure deficit (VPD), PgLEA7 was significantly expressed under high VPD and was selected for functional validation. In silico analysis of the PgLEA promoter regions revealed abiotic stress-specific cis-acting elements such as ABRE, CCAAT, MYBS, and LTRE. Based on the type of motifs, PgLEAPC promoter (758 bp), its deletion 1 (PgLpd1, 349 bp) and deletion 2 (PgLpd2, 125 bp) were cloned into the plant expression vector pMDC164 having the promoter-less uidA gene. All the three plant expression vectors were introduced into tobacco through Agrobacterium tumefaciens-mediated transformation to obtain T₁ and T₂ generations of transgenic plants. Based on expression of the uidA gene, tissue-specific expression was observed in mature stems, roots and seedlings of PgLEAPC and PgLpd1 carrying transgenics only. While the transgenic PgLEAPC plants displayed significantly higher uidA expression in the stem and root tissues under salt, drought, heat, and cold stresses, very low or no expression was observed in PgLpd1 and PgLpd2 transgenics under the tested stress conditions. The results of this study indicate that the complete promoter of PgLEAPC plays a role in developing abiotic stress tolerance in plants.

A NAC transcription factor OsNAC3 positively regulates ABA response and salt tolerance in rice

BACKGROUND

NAC (NAM, ATAF and CUC) transcription factors (TFs) play vital roles in plant development and abiotic stress tolerance. Salt stress is one of the most limiting factors for rice growth and production. However, the mechanism underlying salt tolerance in rice is still poorly understood.

RESULTS

In this study, we functionally characterized a rice NAC TF OsNAC3 for its involvement in ABA response and salt tolerance. ABA and NaCl treatment induced OsNAC3 expression in roots. Immunostaining showed that OsNAC3 was localized in all root cells. OsNAC3 knockout decreased rice plants' sensitivity to ABA but increased salt stress sensitivity, while OsNAC3 overexpression showed an opposite effect. Loss of OsNAC3 also induced Na⁺ accumulation in the shoots. Furthermore, qRT-PCR and transcriptomic analysis were performed to identify the key OsNAC3 regulated genes related to ABA response and salt tolerance, such as OsHKT1;4, OsHKT1;5, OsLEA3-1, OsPM-1, OsPP2C68, and OsRAB-21.

CONCLUSIONS

This study shows that rice OsNAC3 is an important regulatory factor in ABA signal response and salt tolerance.

Toward Integrated Multi-Omics Intervention: Rice Trait Improvement and Stress Management

Rice (Oryza sativa) is an imperative staple crop for nearly half of the world's population. Challenging environmental conditions encompassing abiotic and biotic stresses negatively impact the quality and yield of rice. To assure food supply for the unprecedented ever-growing world population, the improvement of rice as a crop is of utmost importance. In this era, "omics" techniques have been comprehensively utilized to decipher the regulatory mechanisms and cellular intricacies in rice. Advancements in omics technologies have provided a strong platform for the reliable exploration of genetic resources involved in rice trait development. Omics disciplines like genomics, transcriptomics, proteomics, and metabolomics have significantly contributed toward the achievement of desired improvements in rice under optimal and stressful environments. The present review recapitulates the basic and applied multi-omics technologies in providing new orchestration toward the improvement of rice desirable traits. The article also provides a catalog of current scenario of omics applications in comprehending this imperative crop in relation to yield enhancement and various environmental stresses. Further, the appropriate databases in the field of data science to analyze big data, and retrieve relevant information vis-à-vis rice trait improvement and stress management are described.

Involvement of rice transcription factor OsERF19 in response to ABA and salt stress responses

Soil salinity is a major environmental stressor that restricts the growth and yield of crops. Plants have evolved more complicated and precise mechanisms to cope with salt stress, as they cannot escape from harmful environments. In the current study we identified and characterized an AP2/ERF transcription factor in rice, OsERF19. The expression of OsERF19 was slightly repressed by salt stress or abscisic acid (ABA) treatment. OsERF19-overexpression (OsERF19-OX) plants displayed enhanced tolerance to salt stress and ABA hypersensitivity compared to wild type and control plants. Furthermore, OsLEA3, OsNHX1, OsHKT6, and OsOTS1 were upregulated in OsERF19-OX plants when the plants were subjected to salt stress. OsRAB21, OsNCED5, and OsP5CS1 were also upregulated in OsERF19-OX plants treated with ABA. Yeast one-hybrid and dual luciferase reporter assays demonstrated that OsERF19 directly targets the promoters of OsOTS1 and OsNCED5 and further increases their transcription. These results suggest that the transcription factor OsERF19 plays a positive role in salt stress and ABA responses in rice.

LEA13 and LEA30 Are Involved in Tolerance to Water Stress and Stomata Density in Arabidopsis thaliana

Late embryogenesis abundant (LEA) proteins are a large protein family that mainly function in protecting cells from abiotic stress, but these proteins are also involved in regulating plant growth and development. In this study, we performed a functional analysis of LEA13 and LEA30 from Arabidopsis thaliana. The results showed that the expression of both genes increased when plants were subjected to drought-stressed conditions. The insertional lines lea13 and lea30 were identified for each gene, and both had a T-DNA element in the regulatory region, which caused the genes to be downregulated. Moreover, lea13 and lea30 were more sensitive to drought stress due to their higher transpiration and stomatal spacing. Microarray analysis of the lea13 background showed that genes involved in hormone signaling, stomatal development, and abiotic stress responses were misregulated. Our results showed that LEA proteins are involved in drought tolerance and participate in stomatal density.

Nuclear translocation of OsMFT1 that is impeded by OsFTIP1 promotes drought tolerance in rice

Drought is the leading environmental threat affecting crop productivity, and plants have evolved a series of mechanisms to adapt to drought stress. The FT-interacting proteins (FTIPs) and phosphatidylethanolamine-binding proteins (PEBPs) play key roles in developmental processes, whereas their roles in the regulation of stress response are still largely unknown. Here, we report that OsFTIP1 negatively regulates drought response in rice. We showed that OsFTIP1 interacts with rice MOTHER OF FT AND TFL1 (OsMFT1), a PEBP that promotes rice tolerance to drought treatment. Further studies discovered that OsMFT1 interacts with two key drought-related transcription factors, OsbZIP66 and OsMYB26, regulating their binding capacity on drought-related genes and thereby enhancing drought tolerance in rice. Interestingly, we found that OsFTIP1 impedes the nucleocytoplasmic translocation of OsMFT1, implying that dynamic modulation of drought-responsive genes by the OsMFT1-OsMYB26 and OsMFT1-OsbZIP66 complexes is integral to OsFTIP1-modulated nuclear accumulation of OsMFT1. Our findings also suggest that OsMFT1 might act as a hitherto unknown nucleocytoplasmic trafficking signal that regulates drought tolerance in rice in response to environmental signals.

Transcriptome profiling of two rice genotypes under mild field drought stress during grain-filling stage

Drought is one of the most critical abiotic stresses that threaten crop production worldwide. This stress affects the rice crop in all stages of rice development; however, the occurrence during reproductive and grain-filling stages has the most impact on grain yield. Although many global transcriptomic studies have been performed during the reproductive stage in rice, very limited information is available for the grain-filling stage. Hence, we intend to investigate how the rice plant responds to drought stress during the grain-filling stage and how the responses change over time under field conditions. Two rice genotypes were selected for RNA-seq analysis: '4610', previously reported as a moderately tolerant breeding line, and Rondo, an elite indica rice cultivar susceptible to drought conditions. Additionally, 10 agronomic traits were evaluated under normal irrigated and drought conditions. Leaf tissues were collected during grain-filling stages at two time points, 14 and 21 days after the drought treatment, from both the drought field and normal irrigated field conditions. Based on agronomic performances, '4610' was less negatively affected than Rondo under mild drought conditions, and expression profiling largely aligned with the phenotypic data. The transcriptomic data indicated that, in general, '4610' had much earlier responses than its counterpart in mitigating the impact of drought stress. Several key genes and gene families related to drought stress or stress-related conditions were found differentially expressed in this study, including transcription factors, drought tolerance genes and reactive oxygen species scavengers. Furthermore, this study identified novel differentially expressed genes (DEGs) without function annotations that may play roles in drought tolerance-related functions. Some of the important DEGs detected in this study can be targeted for future research.

Genome-Wide Analysis of MADS-Box Genes in Foxtail Millet (Setaria italica L.) and Functional Assessment of the Role of SiMADS51 in the Drought Stress Response

MADS-box transcription factors play vital roles in multiple biological processes in plants. At present, a comprehensive investigation into the genome-wide identification and classification of MADS-box genes in foxtail millet (Setaria italica L.) has not been reported. In this study, we identified 72 MADS-box genes in the foxtail millet genome and give an overview of the phylogeny, chromosomal location, gene structures, and potential functions of the proteins encoded by these genes. We also found that the expression of 10 MIKC-type MADS-box genes was induced by abiotic stresses (PEG-6000 and NaCl) and exogenous hormones (ABA and GA), which suggests that these genes may play important regulatory roles in response to different stresses. Further studies showed that transgenic Arabidopsis and rice (Oryza sativa L.) plants overexpressing SiMADS51 had reduced drought stress tolerance as revealed by lower survival rates and poorer growth performance under drought stress conditions, which demonstrated that SiMADS51 is a negative regulator of drought stress tolerance in plants. Moreover, expression of some stress-related genes were down-regulated in the SiMADS51-overexpressing plants. The results of our study provide an overall picture of the MADS-box gene family in foxtail millet and establish a foundation for further research on the mechanisms of action of MADS-box proteins with respect to abiotic stresses.

Improving drought tolerance in rice: Ensuring food security through multi-dimensional approaches

Drought has been highly prevalent around the world especially in Sub-Saharan Africa and South-East Asian countries. Consistent climatic instabilities and unpredictable rainfall patterns are further worsening the situation. Rice is a C₃ staple cereal and an important food crop for the majority of the world's population and drought stress is one of the major growth retarding threats for rice that slashes down grain quality and yield. Drought deteriorates rice productivity and induces various acclimation responses that aids in stress mitigation. However, the complexity of traits associated with drought tolerance has made the understanding of drought stress-induced responses in rice a challenging process. An integrative understanding based on physiological adaptations, omics, transgenic and molecular breeding approaches successively backed up to developing drought stress-tolerant rice. The review represents a step forward to develop drought-resilient rice plants by exploiting the knowledge that collaborates with omics-based developments with integrative efforts to ensure the compilation of all the possible strategies undertaken to develop drought stress-tolerant rice.

Stacking for future: Pyramiding genes to improve drought and salinity tolerance in rice

Abiotic stresses, such as drought and salinity, adversely affect rice production and cause a severe threat to food security. Conventional crop breeding techniques alone are inadequate for achieving drought stress tolerance in crop plants. Using transgenic technology, incremental improvements in tolerance to drought and salinity have been successfully attained via manipulation of gene(s) in several crop species. However, achieving the goal via pyramiding multiple genes from the same or different tolerance mechanisms has received little attention. Pyramiding of multiple genes can be achieved either through breeding, by using marker-assisted selection, or by genetic engineering through molecular stacking co-transformation or re-transformation. Transgene stacking into a single locus has added advantages over breeding or re-transformation since the former assures co-inheritance of genes, contributing to more effective tolerance in transgenic plants for generations. Drought, being a polygenic trait, the potential candidate genes for gene stacking are those contributing to cellular detoxification, osmolyte accumulation, antioxidant machinery, and signaling pathways. Since cellular dehydration is inbuilt in salinity stress, manipulation of these genes results in improving tolerance to salinity along with drought in most of the cases. In this review, attempts have been made to provide a critical assessment of transgenic plants developed through transgene stacking and approaches to achieve the same. Identification and functional validation of more such candidate genes is needed for research programs targeting the gene stacking for developing crop plants with high precision in the shortest possible time to ensure sustainable crop productivity under marginal lands.

Genome-wide identification and expression analysis of late embryogenesis abundant protein-encoding genes in rye (Secale cereale L.)

Late embryogenesis abundant (LEA) proteins are members of a large and highly diverse family that play critical roles in protecting cells from abiotic stresses and maintaining plant growth and development. However, the identification and biological function of genes of Secale cereale LEA (ScLEA) have been rarely reported. In this study, we identified 112 ScLEA genes, which can be divided into eight groups and are evenly distributed on all rye chromosomes. Structure analysis revealed that members of the same group tend to be highly conserved. We identified 12 pairs of tandem duplication genes and 19 pairs of segmental duplication genes, which may be an expansion way of LEA gene family. Expression profiling analysis revealed obvious temporal and spatial specificity of ScLEA gene expression, with the highest expression levels observed in grains. According to the qRT-PCR analysis, selected ScLEA genes were regulated by various abiotic stresses, especially PEG treatment, decreased temperature, and blue light. Taken together, our results provide a reference for further functional analysis and potential utilization of the ScLEA genes in improving stress tolerance of crops.

Genome-Wide Identification and Expression Analysis of OsbZIP09 Target Genes in Rice Reveal Its Mechanism of Controlling Seed Germination

Seed dormancy and germination are key events in plant development and are critical for crop production, and defects in seed germination or the inappropriate release of seed dormancy cause substantial losses in crop yields. Rice is the staple food for more than half of the world's population, and preharvest sprouting (PHS) is one of the most severe problems in rice production, due to a low level of seed dormancy, especially under warm and damp conditions. Therefore, PHS leads to yield loss and a decrease in rice quality and vitality. We reveal that mutation of OsbZIP09 inhibited rice PHS. Analysis of the expression of OsbZIP09 and its encoded protein sequence and structure indicated that OsbZIP09 is a typical bZIP transcription factor that contains conserved bZIP domains, and its expression is induced by ABA. Moreover, RNA sequencing (RNA-seq) and DNA affinity purification sequencing (DAP-seq) analyses were performed and 52 key direct targets of OsbZIP09 were identified, including OsLOX2 and Late Embryogenesis Abundant (LEA) family genes, which are involved in controlling seed germination. Most of these key targets showed consistent changes in expression in response to abscisic acid (ABA) treatment and OsbZIP09 mutation. The data characterize a number of key target genes that are directly regulated by OsbZIP09 and contribute to revealing the molecular mechanism that underlies how OsbZIP09 controls rice seed germination.

Global insights to drought stress perturbed genes in oat (Avena sativa L.) seedlings using RNA sequencing

Oat (Avena sativa L.) is an important crop in northwestern China. Drought stress is the most significant factor affecting oat yield. In the present study, we explored the changes that occur in oats under drought stress conditions at a global genomic level. RNA sequencing was performed using 15-day-old oat seedlings. The differentially expressed transcripts were identified, and their related functions and pathways were investigated. In total, 1,065 unigenes were differentially expressed in oats under drought stress conditions. Of these, 386 unigenes were upregulated and 679 were downregulated. The perturbed transcripts were closely related to the biosynthesis of secondary metabolites, plant hormone signal transduction, and biosynthesis of antibiotics. DN50483_c0_g1_i3, which was annotated as acetyl-CoA carboxylase, was a significant node in the protein-protein interaction network. Biosynthesis of antibiotics and secondary metabolites may be involved in the drought stress response mechanisms of oats. The perturbed transcripts may provide targets for improving plant stress responses.

OsNBL1, a Multi-Organelle Localized Protein, Plays Essential Roles in Rice Senescence, Disease Resistance, and Salt Tolerance

BACKGROUND

Plant senescence is a complicated process involving multiple regulations, such as temperature, light, reactive oxygen species (ROS), endogenous hormone levels, and diseases. Although many such genes have been characterized to understand the process of leaf senescence, there still remain many unknowns, and many more genes need to be characterized.

RESULTS

We identified a rice mutant nbl1 with a premature leaf senescence phenotype. The causative gene, OsNBL1, encodes a small protein with 94 amino acids, which is conserved in monocot, as well as dicot plants. Disruption of OsNBL1 resulted in accelerated dark-induced leaf senescence, accompanied by a reduction in chlorophyll content and up-regulation of several senescence-associated genes. Notably, the nbl1 mutant was more susceptible to rice blast and bacterial blight but more tolerant to sodium chloride. Several salt-induced genes, including HAK1, HAK5, and three SNAC genes, were also up-regulated in the nbl1 mutant. Additionally, the nbl1 mutant was more sensitive to salicylic acid. Plants overexpressing OsNBL1 showed delayed dark-induced senescence, consistent with a higher chlorophyll content compared to wild-type plants. However, the overexpression plants were indistinguishable from the wild-types for resistance to the rice blast disease. OsNBL1 is a multi-organelle localized protein and interacts with OsClpP6, which is associated with senescence.

CONCLUSIONS

We described a novel leaf senescence mutant nbl1 in rice. It is showed that OsNBL1, a multi-organelle localized protein which interacts with a plastidic caseinolytic protease OsClpP6, is essential for controlling leaf senescence, disease resistance, and salt tolerance.

A R2R3-MYB Transcription Factor Gene, BpMYB123, Regulates BpLEA14 to Improve Drought Tolerance in Betula platyphylla

Drought stress causes various negative impacts on plant growth and crop production. R2R3-MYB transcription factors (TFs) play crucial roles in the response to abiotic stress. However, their functions in Betula platyphylla haven't been fully investigated. In this study, a R2R3 MYB transcription factor gene, BpMYB123, was identified from Betula platyphylla and reveals its significant role in drought stress. Overexpression of BpMYB123 enhances tolerance to drought stress in contrast to repression of BpMYB123 by RNA interference (RNAi) in transgenic experiment. The overexpression lines increased peroxidase (POD) and superoxide dismatase (SOD) activities, while decreased hydrogen peroxide (H₂O₂), superoxide radicals (O₂ ^-), electrolyte leakage (EL) and malondialdehyde (MDA) contents. Our study showed that overexpression of BpMYB123 increased BpLEA14 gene expression up to 20-fold due to BpMYB123 directly binding to the MYB1AT element of BpLEA14 promoter. These results indicate that BpMYB123 acts as a regulator via regulating BpLEA14 to improve drought tolerance in birch.

Seed Priming: A Feasible Strategy to Enhance Drought Tolerance in Crop Plants

Drought is a serious threat to the farming community, biasing the crop productivity in arid and semi-arid regions of the world. Drought adversely affects seed germination, plant growth, and development via non-normal physiological processes. Plants generally acclimatize to drought stress through various tolerance mechanisms, but the changes in global climate and modern agricultural systems have further worsened the crop productivity. In order to increase the production and productivity, several strategies such as the breeding of tolerant varieties and exogenous application of growth regulators, osmoprotectants, and plant mineral nutrients are followed to mitigate the effects of drought stress. Nevertheless, the complex nature of drought stress makes these strategies ineffective in benefiting the farming community. Seed priming is an alternative, low-cost, and feasible technique, which can improve drought stress tolerance through enhanced and advanced seed germination. Primed seeds can retain the memory of previous stress and enable protection against oxidative stress through earlier activation of the cellular defense mechanism, reduced imbibition time, upsurge of germination promoters, and osmotic regulation. However, a better understanding of the metabolic events during the priming treatment is needed to use this technology in a more efficient way. Interestingly, the review highlights the morphological, physiological, biochemical, and molecular responses of seed priming for enhancing the drought tolerance in crop plants. Furthermore, the challenges and opportunities associated with various priming methods are also addressed side-by-side to enable the use of this simple and cost-efficient technique in a more efficient manner.

Whole-genome mining of abiotic stress gene loci in rice

We projected meta-QTL (MQTL) for drought, salinity, cold state, and high metal ion tolerance in rice using a meta-analysis based on high-density consensus maps. In addition, a genome-wide association analysis was used to validate the results of the meta-analysis, and four new chromosome intervals for mining abiotic stress candidate genes were obtained. Drought, severe cold, high salinity, and high metallic ion concentrations severely restrict rice production. Consequently, the breeding of abiotic stress-tolerant variety is being paid increasingly more attention. This study aimed to identify meta-quantitative trait loci (MQTL) for abiotic stress tolerance in rice, as well as the molecular markers and potential candidate genes of the MQTL regions. We summarized 2785 rice QTL and conducted a meta-analysis of 159 studies. We found 82 drought tolerance (DT), 70 cold tolerance (CT), 70 salt tolerance (ST), and 51 heavy metal ion tolerance (IT) meta-QTL, as well as 20 DT, 11 CT, 22 ST, and 5 IT candidate genes in the MQTL interval. Thirty-one multiple-tolerance related MQTL regions, which were highly enriched, were also detected, and 13 candidate genes related to multiple-tolerance were obtained. In addition, the correlation between DT, CT, and ST was significant in the rice genome. Four candidate genes and four MM-QTL regions were detected simultaneously by GWAS and meta-analysis. The four candidate genes showed distinct genetic differentiation and substantial genetic distance between indica and japonica rice, and the four MM-QTL are potential intervals for mining abiotic stress-related candidate genes. The candidate genes identified in this study will not only be useful for marker-assisted selection and pyramiding but will also accelerate the fine mapping and cloning of the candidate genes associated with abiotic stress-tolerance mechanisms in rice.

Rice immune sensor XA21 differentially enhances plant growth and survival under distinct levels of drought

Drought is a complex stress that limits plant growth and crop production worldwide. The mechanisms by which plants coordinately respond to distinct levels of water deficits (e.g., mild, moderate or severe drought) remain elusive. Here we demonstrate that the rice immune sensor XA21 promotes survival of rice seedlings during dehydration stress. XA21 expression increases deposition of lignin and cellulose in the xylem vessels and their surrounding cells. Inhibition of aquaporin water channels by mercuric chloride eliminates XA21-mediated dehydration survival, suggesting that XA21 enables plant survival during drought, probably by protecting xylem functionality. In contrast to prevailing observations of stress tolerance genes, XA21 is also capable of enhancing rice growth during moderate drought. Thus, XA21 acts as a mediator for stress protection and plant growth under water-limiting conditions.

Transcriptomic divergence between upland and lowland ecotypes contributes to rice adaptation to a drought-prone agroecosystem

INTRODUCTION

Transcriptomic divergence drives plant ecological adaptation. Upland rice is differentiated in drought tolerance from lowland rice during its adaptation to the drought-prone environment. They provide a good system to learn the evolution of drought tolerance in rice.

METHODS AND RESULTS

We estimate morphological differences between the two rice ecotypes under well-watered and drought conditions, as well as their genetic and transcriptomic divergences by the high-throughput sequencing. Upland rice possesses higher expression diversity than lowland rice does. Thousands of genes exhibit expression divergences between the two rice ecotypes, which contributes to their morphological differences in drought tolerance. These transcriptomic divergences contribute to drought adaptation of upland rice during its domestication. Mutations in transcriptional regulatory regions, which cause presence and absence of cis-elements, are the cause of expression divergence. About 15.3% transcriptionally selected genes also receive sequence-based selection in upland or lowland ecotype. Some highly differentiated genes promote the transcriptomic divergence between rice ecotypes via gene co-expression network. In addition, we also detected transcriptomic trade-offs between drought tolerance and productivity.

DISCUSSION

Many key genes, which promote transcriptomic adaptation to drought in upland rice, have great prospective in breeding water-saving and drought-resistant rice. Meanwhile, appropriate strategies are required in breeding to overcome the potential transcriptomic trade-off.

Overexpression of OsC3H10, a CCCH-Zinc Finger, Improves Drought Tolerance in Rice by Regulating Stress-Related Genes

CCCH zinc finger proteins are members of the zinc finger protein family, and are known to participate in the regulation of development and stress responses via the posttranscriptional regulation of messenger RNA in animals and yeast. However, the molecular mechanism of CCCHZF-mediated drought tolerance is not well understood. We analyzed the functions of OsC3H10, a member of the rice CCCHZF family. OsC3H10 is predominantly expressed in seeds, and its expression levels rapidly declined during seed imbibition. The expression of OsC3H10 was induced by drought, high salinity and abscisic acid (ABA). Subcellular localization analysis revealed that OsC3H10 localized not only in the nucleus but also to the processing bodies and stress granules upon stress treatment. Root-specific overexpression of OsC3H10 was insufficient to induce drought tolerance, while the overexpression of OsC3H10 throughout the entire plant enhanced the drought tolerance of rice plants. Transcriptome analysis revealed that OsC3H10 overexpression elevated the expression levels of genes involved in stress responses, including LATE EMBRYOGENESIS ABUNDANT PROTEINs (LEAs), PATHOGENESIS RELATED GENEs (PRs) and GERMIN-LIKE PROTEINs (GLPs). Our results demonstrated that OsC3H10 is involved in the regulation of the drought tolerance pathway by modulating the expression of stress-related genes.

PheASR2, a novel stress-responsive transcription factor from moso bamboo (Phyllostachys edulis), enhances drought tolerance in transgenic rice via increased sensitivity to abscisic acid

Abscisic acid, stress and ripening (ASR) transcription factors comprise a small family of proteins that play a key role in stress responses in plants. ASR genes involved in drought tolerance in moso bamboo (Phyllostachys edulis) are largely unknown. In our study, an ASR gene, PheASR2, was isolated and characterized. The expression of PheASR2 was up-regulated under various abiotic stresses, including drought, salt and abscisic acid (ABA). PheASR2 was localized in the nucleus in tobacco cells, and displayed transactivation activity in yeast. Ectopic expression of PheASR2 in rice conferred enhanced tolerance to drought stress, as determined through physiological analyses of germination rate, plant height, water loss and survival rate. The PheASR2-overexpressing transgenic plants showed an increase in reactive oxygen species (ROS), electrolyte leakage and malondialdehyde levels, reduced enzyme (CAT and SOD) activities, and higher expression of genes encoding ROS-scavenging enzymes. Consequently, the transgenic plants exhibited increased tolerance to oxidative stress compared with wild-type plants. Moreover, following ABA treatment, the seed germination rate and plant height of the PheASR2-overexpressing lines were inhibited, and stomatal closure was reduced. The expression of marker genes, including, OsAREB, OsP5CS1, OsLEA, and OsNCED2, was up-regulated in the PheASR2-overexpressing lines when subjected to drought treatment. Together, these results indicate that PheASR2 functions in drought stress tolerance through ABA signaling.

Fine-Mapping of Sorghum Stay-Green QTL on Chromosome10 Revealed Genes Associated with Delayed Senescence

This study was conducted to dissect the genetic basis and to explore the candidate genes underlying one of the important genomic regions on an SBI-10 long arm (L), governing the complex stay-green trait contributing to post-flowering drought-tolerance in sorghum. A fine-mapping population was developed from an introgression line cross—RSG04008-6 (stay-green) × J2614-11 (moderately senescent). The fine-mapping population with 1894 F₂ was genotyped with eight SSRs and a set of 152 recombinants was identified, advanced to the F₄ generation, field evaluated with three replications over 2 seasons, and genotyped with the GBS approach. A high-resolution linkage map was developed for SBI-10L using 260 genotyping by sequencing—Single Nucleotide Polymorphism (GBS–SNPs). Using the best linear unpredicted means (BLUPs) of the percent green leaf area (%GL) traits and the GBS-based SNPs, we identified seven quantitative trait loci (QTL) clusters and single gene, mostly involved in drought-tolerance, for each QTL cluster, viz., AP2/ERF transcription factor family (Sobic.010G202700), NBS-LRR protein (Sobic.010G205600), ankyrin-repeat protein (Sobic.010G205800), senescence-associated protein (Sobic.010G270300), WD40 (Sobic.010G205900), CPK1 adapter protein (Sobic.010G264400), LEA2 protein (Sobic.010G259200) and an expressed protein (Sobic.010G201100). The target genomic region was thus delimited from 15 Mb to 8 genes co-localized with QTL clusters, and validated using quantitative real-time (qRT)–PCR.

Correlation between gene expression levels under drought stress and synonymous codon usage in rice plant by in-silico study

We studied the correlation of synonymous codon usage (SCU) on gene expression levels under drought stress in rice. Sixty genes related to drought stress (with high, intermediate and low expression) were selected from rice meta-analysis data and various codon usage indices such as the effective number of codon usage (ENC), codon adaptation index (CAI) and relative synonymous codon usage (RSCU) were calculated. We found that in genes highly expressing under drought 1) GC content was higher, 2) ENC value was lower, 3) the preferred codons of some amino acids changed and 4) the RSCU ratio of GC-end codons relative to AT-end codons for 18 amino acids increased significantly compared with those in other genes. We introduce ARSCU as the Average ratio of RSCUs of GC-end codons to AT-end codons in each gene that could significantly separate high-expression genes under drought from low-expression genes. ARSCU is calculated using the program ARSCU-Calculator developed by our group to help predicting expression level of rice genes under drought. An index above ARSCU threshold is expected to indicate that the gene under study may belong to the "high expression group under drought". This information may be applied for codon optimization of genes for rice genetic engineering. To validate these findings, we further used 60 other genes (randomly selected subset of 43233 genes studied for their response to drought stress). ARSCU value was able to predict the level of expression at 88.33% of the cases. Using third set of 60 genes selected amongst high expressing genes not related to drought, only 31.65% of the genes showed ARSCU value of higher than the set threshold. This indicates that the phenomenon we described in this report may be unique for drought related genes. To justify the observed correlation between CUB and high expressing genes under drought, possible role of tRNA post transcriptional modification and tRFs was hypothesized as possible underlying biological mechanism.

The trihelix transcription factor OsGTγ-2 is involved adaption to salt stress in rice

OsGTγ-2, a trihelix transcription factor, is a positive regulator of rice responses to salt stress by regulating the expression of ion transporters. Salinity stress seriously restricts rice growth and yield. Trihelix transcription factors (GT factors) specifically bind to GT elements and play a diverse role in plant morphological development and responses to abiotic stresses. In our previous study, we found that the GT-1 element (GAAAAA) is a key element in the salinity-induced OsRAV2 promoter. Here, we identified a rice OsGTγ family member, OsGTγ-2, which directly interacted with the GT-1 element in the OsRAV2 promoter. OsGTγ-2 specifically targeted the nucleus, was mainly expressed in roots, sheathes, stems and seeds, and was induced by salinity, osmotic and oxidative stresses and abscisic acid (ABA). The seed germination rate, seedling growth and survival rate under salinity stress was improved in OsGTγ-2 overexpressing lines (P_ZmUbi::OsGTγ-2). In contrast, CRISPR/Cas9-mediated OsGTγ-2 knockout lines (osgtγ-2) showed salt-hypersensitive phenotypes. In response to salt stress, different Na⁺ and K⁺ acclamation patterns were observed in P_ZmUbi::OsGTγ-2 lines and osgtγ-2 plants were observed. The molecular mechanism of OsGTγ-2 in rice salt adaptation was also investigated. Several major genes responsible for ion transporting, such as the OsHKT2; 1, OsHKT1; 3 and OsNHX1 were transcriptionally regulated by OsGTγ-2. A subsequent yeast one-hybrid assay and EMSA indicated that OsGTγ-2 directly interacted with the promoters of OsHKT2; 1, OsNHX1 and OsHKT1; 3. Taken together, these results suggest that OsGTγ-2 is an important positive regulator involved in rice responses to salt stress and suggest a potential role for OsGTγ-2 in regulating salinity adaptation in rice.

A lamin-like protein OsNMCP1 regulates drought resistance and root growth through chromatin accessibility modulation by interacting with a chromatin remodeller OsSWI3C in rice

Lamin proteins in animals are implicated in important nuclear functions, including chromatin organization, signalling transduction, gene regulation and cell differentiation. Nuclear Matrix Constituent Proteins (NMCPs) are lamin analogues in plants, but their regulatory functions remain largely unknown. We report that OsNMCP1 is localized at the nuclear periphery in rice (Oryza sativa) and induced by drought stress. OsNMCP1 overexpression resulted in a deeper and thicker root system, and enhanced drought resistance compared to the wild-type control. An assay for transposase accessible chromatin with sequencing (ATAC-seq) analysis revealed that OsNMCP1-overexpression altered chromatin accessibility in hundreds of genes related to drought resistance and root growth, including OsNAC10, OsERF48, OsSGL, SNAC1 and OsbZIP23. OsNMCP1 can interact with SWITCH/SUCROSE NONFERMENTING (SWI/SNF) chromatin remodelling complex subunit OsSWI3C. The reported drought resistance or root growth-related genes that were positively regulated by OsNMCP1 were negatively regulated by OsSWI3C under drought stress conditions, and OsSWI3C overexpression led to decreased drought resistance. We propose that the interaction between OsNMCP1 and OsSWI3C under drought stress conditions may lead to the release of OsSWI3C from the SWI/SNF gene silencing complex, thus changing chromatin accessibility in the genes related to root growth and drought resistance.

Late Embryogenesis Abundant Protein-Client Protein Interactions

The intrinsically disordered proteins belonging to the LATE EMBRYOGENESIS ABUNDANT protein (LEAP) family have been ascribed a protective function over an array of intracellular components. We focus on how LEAPs may protect a stress-susceptible proteome. These examples include instances of LEAPs providing a shield molecule function, possibly by instigating liquid-liquid phase separations. Some LEAPs bind directly to their client proteins, exerting a holdase-type chaperonin function. Finally, instances of LEAP-client protein interactions have been documented, where the LEAP modulates (interferes with) the function of the client protein, acting as a surreptitious rheostat of cellular homeostasis. From the examples identified to date, it is apparent that client protein modulation also serves to mitigate stress. While some LEAPs can physically bind and protect client proteins, some apparently bind to assist the degradation of the client proteins with which they associate. Documented instances of LEAP-client protein binding, even in the absence of stress, brings to the fore the necessity of identifying how the LEAPs are degraded post-stress to render them innocuous, a first step in understanding how the cell regulates their abundance.

Genetically modified crops are superior in their nitrogen use efficiency-A meta-analysis of three major cereals

It is currently uncertain to what extent genetic transformations of strategic crops (targeting diverse traits) have improved their N use efficiency (NUE), and what the key factors affecting their NUE are. Based on data collected from 130 publications, the effect sizes of genetic transformations and the key factors influencing NUE for three major cereal crops (rice, maize, and wheat), were investigated using a meta-analysis approach. Genetic transformations increased yield, shoot biomass, N uptake efficiency (NUpE), and partial factor productivity of N (PFPN) in the crops, but decreased shoot NUE (SNUE) and grain NUE (GNUE). Transporter genes improved yield and NUE parameters more efficiently, than did the other gene types. The effect sizes for some NUE parameters varied according to crop species and experimental conditions but did not differ between the overexpression and ectopic expression methods. Most effect sizes did not correlate with gene overexpression levels. These results indicate a promising potential of genetic transformations approaches for improving certain NUE parameters.

AsHSP26.8a, a creeping bentgrass small heat shock protein integrates different signaling pathways to modulate plant abiotic stress response

BACKGROUND

Small heat shock proteins (sHSPs) are critical for plant response to biotic and abiotic stresses, especially heat stress. They have also been implicated in various aspects of plant development. However, the acting mechanisms of the sHSPs in plants, especially in perennial grass species, remain largely elusive.

RESULTS

In this study, AsHSP26.8a, a novel chloroplast-localized sHSP gene from creeping bentgrass (Agrostis stolonifera L.) was cloned and its role in plant response to environmental stress was studied. AsHSP26.8a encodes a protein of 26.8 kDa. Its expression was strongly induced in both leaf and root tissues by heat stress. Transgenic Arabidopsis plants overexpressing AsHSP26.8a displayed reduced tolerance to heat stress. Furthermore, overexpression of AsHSP26.8a resulted in hypersensitivity to hormone ABA and salinity stress. Global gene expression analysis revealed AsHSP26.8a-modulated expression of heat-shock transcription factor gene, and the involvement of AsHSP26.8a in ABA-dependent and -independent as well as other stress signaling pathways.

CONCLUSIONS

Our results suggest that AsHSP26.8a may negatively regulate plant response to various abiotic stresses through modulating ABA and other stress signaling pathways.

LEA Gene Expression Assessment in Advanced Mutant Rice Genotypes under Drought Stress

Late embryogenesis abundant (LEA) proteins are primarily found in plants stem, roots, and other organs and play significant roles in tolerance to several abiotic stresses. Plants synthesize a discrete set of LEA proteins in response to drought stress. In this study, the expression patterns of LEA genes were investigated in two advanced mutant rice genotypes subjected to the drought stress condition and different physiological traits including photosynthetic rate, leaf chlorophyll content, and photosystem II (PSII) photochemical efficiency (Fv/Fm) which were analyzed to confirm their drought tolerance. Five LEA genes (OsLEA1, OsLEA2, OsLEA3, OsLEA4, and OsLEA5) were used in the evaluation of rice genotypes and were significantly upregulated by more than 4-fold for MR219-4 and MR219-9. The upregulated genes by these two varieties showed high similarity with the drought-tolerant check variety, Aeron1. This indicates that these advanced mutant genotypes have better tolerance to drought stress. The changes in the expression level of LEA genes among the selected rice genotypes under drought stress were further confirmed. Hence, LEA genes could be served as a potential tool for drought tolerance determination in rice. MR219-4 and MR219-9 were found to be promising in breeding for drought tolerance as they offer better physiological adaptation to drought stress.

ASR Enhances Environmental Stress Tolerance and Improves Grain Yield by Modulating Stomatal Closure in Rice

Abscisic acid-, stress-, and ripening-induced (ASR) genes are involved in responding to abiotic stresses, but their precise roles in enhancing grain yield under stress conditions remain to be determined. We cloned a rice (Oryza sativa) ASR gene, OsASR1, and characterized its function in rice plants. OsASR1 expression was induced by abscisic acid (ABA), salt, and drought treatments. Transgenic rice plants overexpressing OsASR1 displayed improved water regulation under salt and drought stresses, which was associated with osmolyte accumulation, improved modulation of stomatal closure, and reduced transpiration rates. OsASR1-overexpressing plants were hypersensitive to exogenous ABA and accumulated higher endogenous ABA levels under salt and drought stresses, indicating that OsASR1 is a positive regulator of the ABA signaling pathway. The growth of OsASR1-overexpressing plants was superior to that of wild-type (WT) plants under paddy field conditions when irrigation was withheld, likely due to improved modulation of stomatal closure via modified ABA signaling. The transgenic plants had higher grain yields than WT plants for four consecutive generations. We conclude that OsASR1 has a crucial role in ABA-mediated regulation of stomatal closure to conserve water under salt- and drought-stress conditions, and OsASR1 overexpression can enhance salinity and drought tolerance, resulting in improved crop yields.

Interactive role of salicylic acid and nitric oxide on transcriptional reprogramming for high temperature tolerance in lablab purpureus L.: Structural and functional insights using computational approaches

Salicylic acid (SA) and nitric oxide (NO) are considered as putative plant growth regulators that are involved in the regulation of an array of plant's growth and developmental functions under environmental fluctuations when applied at lower concentrations. The possible involvement of NO in SA induced attenuation of high temperature (HT) induced oxidative stress in plants is however, still vague and need to be explored. Therefore, the present study aimed to investigates the biochemical and physiological changes induced by foliar spray of SA and NO combinations to ameliorate HT induced oxidative stress in Lablab purpureus L. Foliar application of combined SA and NO significantly improved relative water content (27.8 %), photosynthetic pigment content (67.2 %), membrane stability (45 %), proline content (1.0 %), expression of enzymatic antioxidants (7.1-18 %) along with pod yield (1.0 %). Heat Shock Factors (HSFs) play crucial roles in plants abiotic stress tolerance, however there structural and functional classifications in L. purpureus L. is still unknown. So, In-silico approach was also used for functional characterization and homology modelling of HSFs in L. purpureus. The experimental findings depicted that combine effect of SA and NO enhances tolerance in HT stressed L. purpureus L. plants by regulating physiological functions, antioxidants, expression and regulation of stress-responsive genes via transcriptional regulation of heat shock factor.

The quest for osmosensors in plants

Osmotic stress has severe effects on crop productivity. Since climate change is predicted to exacerbate this problem, the development of new crops that are tolerant to osmotic stresses, especially drought and salinity stress, is required. However, only limited success has been achieved to date, primarily because of the lack of a clear understanding of the mechanisms that facilitate osmosensing. Here, we discuss the potential mechanisms of osmosensing in plants. We highlight the roles of proteins such as receptor-like kinases, which sense stress-induced cell wall damage, mechanosensitive calcium channels, which initiate a calcium-induced stress response, and phospholipase C, a membrane-bound enzyme that is integral to osmotic stress perception. We also discuss the roles of aquaporins and membrane-bound histidine kinases, which could potentially detect changes in extracellular osmolarity in plants, as they do in prokaryotes and lower eukaryotes. These putative osmosensors have the potential to serve as master regulators of the osmotic stress response in plants and could prove to be useful targets for the selection of osmotic stress-tolerant crops.

A U-box E3 ubiquitin ligase OsPUB67 is positively involved in drought tolerance in rice

OsPUB67, a U-box E3 ubiquitin ligase, may interact with two drought tolerance negative regulators (OsRZFP34 and OsDIS1) and improve drought tolerance by enhancing the reactive oxygen scavenging ability and stomatal closure. E3 ubiquitin ligases are major components of the ubiquitination cascade and contribute to the biotic and abiotic stress response in plants. In the present study, we show that a rice drought responsive gene, OsPUB67, encoding the U-box E3 ubiquitin ligase was significantly induced by drought, salt, cold, JA, and ABA, and was expressed in nuclei, cytoplasm, and membrane systems. This distribution of expression suggests a significant role for OsPUB67 in a wide range of biological processes and abiotic stress response. Over-expression of OsPUB67 improved drought stress tolerance by enhancing the reactive oxygen scavenging ability and stomatal closure. Bimolecular fluorescence complementation assays revealed that a few E2s interacted with OsPUB67 with unique functional implications in different cell components. Further evidence showed that several E3 ubiquitin ligases interacted with OsPUB67, especially OsRZFP34 and OsDIS1, which are negative regulators of drought tolerance. This interaction on the stomata implied OsPUB67 might function as a heterodimeric ubiquitination complex in response to drought stress. Comprehensive transcriptome analysis revealed OsPUB67 participated in regulating genes involved in the abiotic stress response and transcriptional regulation in an ABA-dependent manner. Our findings revealed OsPUB67 mediated a multilayered complex drought stress tolerance mechanism.

A MYB-related transcription factor from sheepgrass, LcMYB2, promotes seed germination and root growth under drought stress

BACKGROUND

Drought is one of the most serious factors limiting plant growth and production. Sheepgrass can adapt well to various adverse conditions, including drought. However, during germination, sheepgrass young seedlings are sensitive to these adverse conditions. Therefore, the adaptability of seedlings is very important for plant survival, especially in plants that inhabit grasslands or the construction of artificial grassland.

RESULTS

In this study, we found a sheepgrass MYB-related transcription factor, LcMYB2 that is up-regulated by drought stress and returns to a basal level after rewatering. The expression of LcMYB2 was mainly induced by osmotic stress and was localized to the nucleus. Furthermore, we demonstrate that LcMYB2 promoted seed germination and root growth under drought and ABA treatments. Additionally, we confirmed that LcMYB2 can regulate LcDREB2 expression in sheepgrass by binding to its promoter, and it activates the expression of the osmotic stress marker genes AtDREB2A, AtLEA14 and AtP5CS1 by directly binding to their promoters in transgenic Arabidopsis.

CONCLUSIONS

Based on these results, we propose that LcMYB2 improves plant drought stress tolerance by increasing the accumulation of osmoprotectants and promoting root growth. Therefore, LcMYB2 plays pivotal roles in plant responses to drought stress and is an important candidate for genetic manipulation to create drought-resistant crops, especially during seed germination.

Deciphering Root Architectural Traits Involved to Cope With Water Deficit in Oat

Drought tolerance is a complex phenomenon comprising many physiological, biochemical and morphological changes at both aerial and below ground levels. We aim to reveal changes on root morphology that promote drought tolerance in oat in both seedling and adult plants. To this aim, we employed two oat genotypes, previously characterized as susceptible and tolerant to drought. Root phenotyping was carried out on young plants grown either in pots or in rhizotrons under controlled environments, and on adult plants grown in big containers under field conditions. Overall, the tolerant genotype showed an increased root length, branching rate, root surface, and length of fine roots, while coarse to fine ratio decreased as compared with the susceptible genotype. We also observed a high and significant correlation between various morphological root traits within and between experiments, identifying several of them as appropriate markers to identify drought tolerant oat genotypes. Stimulation of fine root growth was one of the most prominent responses to cope with gradual soil water depletion, in both seedlings and adult plants. Although seedling experiments did not exactly match the response of adult plants, they were similarly informative for discriminating between tolerant and susceptible genotypes. This might contribute to easier and faster phenotyping of large amount of plants.

Involvement of OsGF14b Adaptation in the Drought Resistance of Rice Plants

BACKGROUND

Drought stress is one of the major abiotic stresses that restrict plant growth and development. 14-3-3 proteins have been validated to regulate many biological processes in plants. Previous research demonstrated that OsGF14b plays different roles in panicle and leaf blast resistance. In this study, we researched the function of OsGF14b in drought resistance in rice.

FINDINGS

Here, we report that OsGF14b was strongly induced by soil drought stress. In comparison with wild type (WT), the osgf14b mutant exhibited improved resistance to drought and osmotic stress by changing the content of stress-relevant parameters, complementation of the osgf14b mutant restored the drought sensitivity to WT levels, whereas the OsGF14b-overexpression lines exhibited enhanced sensitivity to drought and osmotic stress. The osgf14b mutant plants were hypersensitive to abscisic acid (ABA), while the OsGF14b-overexpression plants showed reduced sensitivity to ABA. Furthermore, mutation and overexpression of OsGF14b affected the expression of stress-related genes under normal growth conditions and/or drought stress conditions.

CONCLUSIONS

We have demonstrated that OsGF14b is involved in the drought resistance of rice plants, partially in an ABA-dependent manner.

Transgenic crops for the agricultural improvement in Pakistan: a perspective of environmental stresses and the current status of genetically modified crops

Transgenic technologies have emerged as a powerful tool for crop improvement in terms of yield, quality, and quantity in many countries of the world. However, concerns also exist about the possible risks involved in transgenic crop cultivation. In this review, literature is analyzed to gauge the real intensity of the issues caused by environmental stresses in Pakistan. In addition, the research work on genetically modified organisms (GMOs) development and their performance is analyzed to serve as a guide for the scientists to help them select useful genes for crop transformation in Pakistan. The funding of GMOs research in Pakistan shows that it does not follow the global trend. We also present socio-economic impact of GM crops and political dimensions in the seed sector and the policies of the government. We envisage that this review provides guidelines for public and private sectors as well as the policy makers in Pakistan and in other countries that face similar environmental threats posed by the changing climate.

CRISPR-associated nucleases: the Dawn of a new age of efficient crop improvement

The world stands at a new threshold today. As a planet, we face various challenges, and the key one is how to continue to produce enough food, feed, fiber, and fuel to support the burgeoning population. In the past, plant breeding and the ability to genetically engineer crops contributed to increasing food production. However, both approaches rely on random mixing or integration of genes, and the process can be unpredictable and time-consuming. Given the challenge of limited availability of natural resources and changing environmental conditions, the need to rapidly and precisely improve crops has become urgent. The discovery of CRISPR-associated endonucleases offers a precise yet versatile platform for rapid crop improvement. This review summarizes a brief history of the discovery of CRISPR-associated nucleases and their application in genome editing of various plant species. Also provided is an overview of several new endonucleases reported recently, which can be utilized for editing of specific genes in plants through various forms of DNA sequence alteration. Genome editing, with its ever-expanding toolset, increased efficiency, and its potential integration with the emerging synthetic biology approaches hold promise for efficient crop improvement to meet the challenge of supporting the needs of future generations.

Overexpression of a microRNA-targeted NAC transcription factor improves drought and salt tolerance in Rice via ABA-mediated pathways

BACKGROUND

The NAC (NAM, AFAT, and CUC) transcription factors play critical roles in rice (Oryza sativa) development and stress regulation. Overexpressing a microRNA (miR164b)-resistant OsNAC2 mutant gene, which generates transcripts that cannot be targeted by miR164b, improves rice plant architecture and yield; however, the performance of these mOsNAC2-overexpressing lines, named ZUOErN3 and ZUOErN4, under abiotic stress conditions such as drought have not yet been fully characterized.

RESULTS

In this study, we showed that the germination of ZUOErN3 and ZUOErN4 seeds was delayed in comparison with the wild-type (WT) seeds, although the final germination rates of all lines were over 95%. The quantification of the endogenous ABA levels revealed that the germinating mOsNAC2-overexpressing seeds had elevated ABA levels, which resulted in their slower germination. The mOsNAC2-overexpressing plants were significantly more drought tolerance than the WT plants, with the survival rate increasing from 11.2% in the WT to nearly 70% in ZUOErN3 and ZUOErN4 plants after a drought treatment. Salt (NaCl) tolerance was also increased in the ZUOErN3 and ZUOErN4 plants due to significantly increased ABA levels. A reverse transcription quantitative PCR (RT-qPCR) analysis showed a significant increase in the expression of the ABA biosynthesis genes OsNCED1 and OsNCED3 in the mOsNAC2-overexpressing lines, and the expression levels of the stress-responsive genes OsP5CS1, OsLEA3, and OsRab16 were significantly increased in these plants. Moreover, OsNAC2 directly interacted with the promoters of OsLEA3 and OsNCED3 in yeast one-hybrid assays.

CONCLUSIONS

Taken together, our results show that OsNAC2 plays a positive regulatory role in drought and salt tolerance in rice through ABA-mediated pathways.

UV-B priming of Oryza sativa var. Kanchana seedlings augments its antioxidative potential and gene expression of stress-response proteins under various abiotic stresses

Priming is one of the mechanisms for the induction of the antioxidant defense system and various stress-responsive proteins which help plants to survive under various abiotic stresses. Based on the observation that the rice seedlings primed with UV-B (low dose of UV-B irradiation-6 kJm^-2) induced the acclimation against NaCl, PEG and UV-B stresses, it was of interest to see the augmentation of antioxidative potential and stress-responsive proteins accumulation in rice seedlings due to UV-B priming under these stresses. Various stresses result in production of ROS, which cause membrane degradation resulting in the accumulation of malondialdehyde. These negative impacts were observed exceedingly in rice seedlings from non-primed PEG stress (NP+P) condition than UV-B and NaCl stresses. The production of non-enzymatic antioxidants, activity/mRNA-level expressions of enzymatic antioxidants and stress-responsive proteins were effectively augmented in UV-B-primed rice seedlings subjected to NaCl stress (P+N) condition followed by UV-B stress (P+U) and PEG stress (P+P). The activation of stress-responsive proteins (HSP and LEA) in rice due to the UV-B priming of rice seedlings is being reported for the first time. The results revealed that the UV-B seedling priming was alleviating the effect of NaCl, PEG, and UV-B stresses in rice seedlings. The positive impacts of UV-B seedling priming were more prominent in rice seedlings subjected to NaCl stress, indicating the cross tolerance imparted by UV-B priming.

OsNCED5, a 9-cis-epoxycarotenoid dioxygenase gene, regulates salt and water stress tolerance and leaf senescence in rice

9-cis-epoxycarotenoid dioxygenase (NCED) is a rate-limiting enzyme for abscisic acid (ABA) biosynthesis. However, the molecular mechanisms of NCED5 that modulate plant development and abiotic stress tolerance are still unclear, particular in rice. Here, we demonstrate that a rice NCED gene, OsNCED5, was expressed in all tissues we tested, and was induced by exposure to salt stress, water stress, and darkness. Mutational analysis showed that nced5 mutants reduced ABA level and decreased tolerance to salt and water stress and delayed leaf senescence. However, OsNCED5 overexpression increased ABA level, enhanced tolerance to the stresses, and accelerated leaf senescence. Transcript analysis showed that OsNCED5 regulated ABA-dependent abiotic stress and senescence-related gene expression. Additionally, ectopic expression of OsNCED5 tested in Arabidopsis thaliana altered plant size and leaf morphology and delayed seed germination and flowering time. Thus, OsNCED5 may regulate plant development and stress resistance through control of ABA biosynthesis. These findings contribute to our understanding of the molecular mechanisms by which NCED regulates plant development and responses to abiotic stress in different crop species.

Genome-Wide Identification and Expression Profiles of Late Embryogenesis-Abundant (LEA) Genes during Grain Maturation in Wheat (Triticum aestivum L.)

Late embryogenesis-abundant (LEA) genes play important roles in plant growth and development, especially the cellular dehydration tolerance during seed maturation. In order to comprehensively understand the roles of LEA family members in wheat, we carried out a series of analyses based on the latest genome sequence of the bread wheat Chinese Spring. 121 Triticum aestivum L. LEA (TaLEA) genes, classified as 8 groups, were identified and characterized. TaLEA genes are distributed in all chromosomes, most of them with a low number of introns (≤3). Expression profiles showed that most TaLEA genes expressed specifically in grains. By qRT-PCR analysis, we confirmed that 12 genes among them showed high expression levels during late stage grain maturation in two spring wheat cultivars, Yangmai16 and Yangmai15. For most genes, the peak of expression appeared earlier in Yangmai16. Statistical analysis indicated that expression level of 8 genes in Yangmai 16 were significantly higher than Yangmai 15 at 25 days after anthesis. Taken together, our results provide more knowledge for future functional analysis and potential utilization of TaLEA genes in wheat breeding.

Identification, characterization and expression analysis of lineage-specific genes within Triticeae

Lineage-specific genes (LSGs) are a set of genes in a given taxon without significant sequence similarity to genes and intergenic sequences of other taxa and are functional. The tribe Triticeae mainly includes species of different ploidy levels, such as staple food crops wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). This study is aimed at mining and characterizing the Triticeae-specific genes (TSGs) using expressed sequence data of wheat. A total of 3812 TSGs was identified and they were generally characterized by smaller size, fewer exons, shorter open reading frames and lower expression levels. Most TSGs were expressed with tissue preference and many of them were predominantly expressed in reproduction related tissues, especially in young stamen. Nearly one third of the TSGs were stress-responsive and inducible under abiotic and/or biotic stresses. A co-expression-based annotation supported the relevance of some TSGs with reproduction and stress responses, indicating their potential economic importance.

Drought Resistance in Rice from Conventional to Molecular Breeding: A Review

Drought is the leading threat to agricultural food production, especially in the cultivation of rice, a semi-aquatic plant. Drought tolerance is a complex quantitative trait with a complicated phenotype that affects different developmental stages in plants. The level of susceptibility or tolerance of rice to several drought conditions is coordinated by the action of different drought-responsive genes in relation with other stress components which stimulate signal transduction pathways. Interdisciplinary researchers have broken the complex mechanism of plant tolerance using various methods such as genetic engineering or marker-assisted selection to develop a new cultivar with improved drought resistance. The main objectives of this review were to highlight the current method of developing a durable drought-resistant rice variety through conventional breeding and the use of biotechnological tools and to comprehensively review the available information on drought-resistant genes, QTL analysis, gene transformation and marker-assisted selection. The response, indicators, causes, and adaptation processes to the drought stress were discussed in the review. Overall, this review provides a systemic glimpse of breeding methods from conventional to the latest innovation in molecular development of drought-tolerant rice variety. This information could serve as guidance for researchers and rice breeders.

Development of Drought-Tolerant Transgenic Wheat: Achievements and Limitations

Crop yield improvement is necessary to keep pace with increasing demand for food. Due to climatic variability, the incidence of drought stress at crop growth stages is becoming a major hindering factor to yield improvement. New techniques are required to increase drought tolerance along with improved yield. Genetic modification for increasing drought tolerance is highly desirable, and genetic engineering for drought tolerance requires the expression of certain stress-related genes. Genes have been identified which confer drought tolerance and improve plant growth and survival in transgenic wheat. However, less research has been conducted for the development of transgenic wheat as compared to rice, maize, and other staple food. Furthermore, enhanced tolerance to drought without any yield penalty is a major task of genetic engineering. In this review, we have focused on the progress in the development of transgenic wheat cultivars for improving drought tolerance and discussed the physiological mechanisms and testing of their tolerance in response to inserted genes under control or field conditions.

A Moso Bamboo Drought-Induced 19 Protein, PeDi19-4, Enhanced Drought and Salt Tolerance in Plants via the ABA-Dependent Signaling Pathway

Here, 10 drought-induced 19 (Di19) proteins from Phyllostachys edulis were analyzed and an important stress-related candidate gene (PeDi19-4) was isolated based on analysis of phylogenetic relationships and expression profiles. PeDi19-4 is a nuclear localization protein that can bind the conserved TACA(A/G)T sequence, as determined using enzyme-linked immunosorbent assay (EMSA). PeDi19-4 has no transcriptional activity in yeast but functions as a transcription activator in plants. Overexpression of PeDi19-4 in rice and Arabidopsis thaliana enhanced drought and salt tolerance as determined through phenotypic analysis and the use of stress-associated physiological indicators. PeDi19-4 transgenic plants showed increased sensitivity to ABA during seed germination and early seedling growth. Additionally, transgenic rice accumulated more ABA than wild-type plants under drought and salt stress conditions. Moreover, the stomata of PeDi19-4-overexpressing plants changed significantly with ABA treatment. RNA sequencing revealed that PeDi19-4 regulated the expression of a wide spectrum of stress-/ABA-responsive differentially expressed genes. The stress-responsive genes (OsZFP252 and OsNAC6) and ABA-responsive genes (OsBZ8 and OsbZIP23) were direct targets of PeDi19-4. Our research indicated that PeDi19-4 enhanced drought and salt tolerance in plants via the ABA-dependent signaling pathway.

Abscisic acid is a substrate of the ABC transporter encoded by the durable wheat disease resistance gene Lr34

The wheat Lr34res allele, coding for an ATP-binding cassette transporter, confers durable resistance against multiple fungal pathogens. The Lr34sus allele, differing from Lr34res by two critical nucleotide polymorphisms, is found in susceptible wheat cultivars. Lr34res is functionally transferrable as a transgene into all major cereals, including rice, barley, maize, and sorghum. Here, we used transcriptomics, physiology, genetics, and in vitro and in vivo transport assays to study the molecular function of Lr34. We report that Lr34res results in a constitutive induction of transcripts reminiscent of an abscisic acid (ABA)-regulated response in transgenic rice. Lr34-expressing rice was altered in biological processes that are controlled by this phytohormone, including dehydration tolerance, transpiration and seedling growth. In planta seedling and in vitro yeast accumulation assays revealed that both LR34res and LR34sus act as ABA transporters. However, whereas the LR34res protein was detected in planta the LR34sus version was not, suggesting a post-transcriptional regulatory mechanism. Our results identify ABA as a substrate of the LR34 ABC transporter. We conclude that LR34res-mediated ABA redistribution has a major effect on the transcriptional response and physiology of Lr34res-expressing plants and that ABA is a candidate molecule that contributes to Lr34res-mediated disease resistance.