Natural Variation in OsLG3 Increases Drought Tolerance in Rice by Inducing ROS Scavenging

Dissecting the molecular basis of the ultra-large grain formation in rice

The shape of rice grains not only determines the thousand-grain weight but also correlates closely with the grain quality. Here we identified an ultra-large grain accession (ULG) with a thousand-grain weight exceeding 60 g. The integrated analysis of QTL, BSA, de novo genome assembled, transcription sequencing, and gene editing was conducted to dissect the molecular basis of the ULG formation. The ULG pyramided advantageous alleles from at least four known grain-shaping genes, OsLG3, OsMADS1, GS3, GL3.1, and one novel locus, qULG2-b, which encoded a leucine-rich repeat receptor-like kinase. The collective impacts of OsLG3, OsMADS1, GS3, and GL3.1 on grain size were confirmed in transgenic plants and near-isogenic lines. The transcriptome analysis identified 112 genes cooperatively regulated by these four genes that were prominently involved in photosynthesis and carbon metabolism. By leveraging the pleiotropy of these genes, we enhanced the grain yield, appearance, and stress tolerance of rice var. SN265. Beyond showcasing the pyramiding of multiple grain size regulation genes that can produce ULG, our study provides a theoretical framework and valuable genomic resources for improving rice variety by leveraging the pleiotropy of grain size regulated genes.

OsBBP1, a newly identified protein containing DUF630 and DUF632 domains confers drought tolerance in rice

Domain of unknown function (DUF) protein families, which are uncharacterized and numerous within the Pfam database. Recently, studies have demonstrated that DUFs played crucial roles in plant development, but whether, or how, they function in drought resistance remain unclear. In this study, we identified the Os03g0321500 gene, encoding OsbZIP72 binding protein 1 (OsBBP1), as a target of OsbZIP72 using chromatin immunoprecipitation sequencing in rice. OsBBP1 is a novel member of DUFs, which localize both in the nuclei and cytoplasm of rice protoplasts. Furthermore, yeast one-hybrid and electrophoretic mobility shift assays confirmed the specific binding between OsbZIP72 and OsBBP1. Additionally, a luciferase reporter analysis illustrated that OsbZIP72 activated the expression of OsBBP1. Drought tolerance experiments demonstrate that the OsBBP1 CRISPER-CAS9 transgenic mutants were sensitive to drought stress, but the transgenic OsBBP1 over-expressing rice plants showed enhanced drought resistance. Moreover, drought tolerance experiments in a paddy field suggested that OsBBP1 contributed to less yield or yield-related losses under drought conditions. Mechanistically, OsBBP1 might confer drought resistance by inducing more efficient reactive oxygen species (ROS) scavenging. Several ROS scavenging-related genes showed increased expression levels in OsBBP1 overexpression lines and decreased expression levels in OsBBP1 CRISPER-CAS9 mutants under drought conditions. Thus, OsBBP1, acting downstream of OsbZIP72, contributes to drought resistance and causes less yield or yield-related losses under drought conditions.

Transcription factor TaNF-YB2 interacts with partners TaNF-YA7/YC7 and transcriptionally activates distinct stress-defensive genes to modulate drought tolerance in T. Aestivum

BACKGROUND

Drought stress limits significantly the crop productivity. However, plants have evolved various strategies to cope with the drought conditions by adopting complex molecular, biochemical, and physiological mechanisms. Members of the nuclear factor Y (NF-Y) transcription factor (TF) family constitute one of the largest TF classes and are involved in plant responses to abiotic stresses.

RESULTS

TaNF-YB2, a NY-YB subfamily gene in T. aestivum, was characterized in this study focusing on its role in mediating plant adaptation to drought stress. Yeast two-hybrid (Y-2 H), biomolecular fluoresence complementation (BiFC), and Co-immunoprecipitation (Co-IP) assays indicated that TaNF-YB2 interacts with the NF-YA member TaNF-YA7 and NF-YC family member TaNF-YC7, which constitutes a heterotrimer TaNF-YB2/TaNF-YA7/TaNF-YC7. The TaNF-YB2 transcripts are induced in roots and aerial tissues upon drought signaling; GUS histochemical staining analysis demonstrated the roles of cis-regulatory elements ABRE and MYB situated in TaNF-YB2 promoter to contribute to target gene response to drought. Transgene analysis on TaNF-YB2 confirmed its functions in regulating drought adaptation via modulating stomata movement, osmolyte biosynthesis, and reactive oxygen species (ROS) homeostasis. TaNF-YB2 possessed the abilities in transcriptionally activating TaP5CS2, the P5CS family gene involving proline biosynthesis and TaSOD1, TaCAT5, and TaPOD5, the genes encoding antioxidant enzymes. Positive correlations were found between yield and the TaNF-YB2 transcripts in a core panel constituting 45 wheat cultivars under drought condition, in which two types of major haplotypes including TaNF-YB2-Hap1 and -Hap2 were included, with the former conferring more TaNF-YB2 transcripts and stronger plant drought tolerance.

CONCLUSIONS

TaNF-YB2 is transcriptional response to drought stress. It is an essential regulator in mediating plant drought adaptation by modulating the physiological processes associated with stomatal movement, osmolyte biosynthesis, and reactive oxygen species (ROS) homeostasis, depending on its role in transcriptionally regulating stress response genes. Our research deepens the understanding of plant drought stress underlying NF-Y TF family and provides gene resource in efforts for molecular breeding the drought-tolerant cultivars in T. aestivum.

Unraveling the Role of the Liriodendron Thioredoxin (TRX) Gene Family in an Abiotic Stress Response

Thioredoxin (TRX) is a small protein with REDOX activity that plays a crucial role in a plant's growth, development, and stress resistance. The TRX family has been extensively studied in Arabidopsis, rice, and wheat, and so it is likely that its members have similar biological functions in Liriodendron that have not been reported in Liriodendron. In this study, we performed the genome-wide identification of the TRX gene family based on the Liriodendron chinense genome, leading to a total of 42 LcTRX gene members. A phylogenetic analysis categorized these 42 LcTRX proteins into 13 subfamilies. We further characterized their chromosome distributions, gene structures, conserved protein motifs, and cis-elements in the promoter regions. In addition, based on the publicly available transcriptome data for Liriodendron hybrid and following RT-qPCR experiments, we explored the expression patterns of LhTRXs to different abiotic stressors, i.e., drought, cold, and heat stress. Notably, we found that several LhTRXs, especially LhTRX-h3, were significantly upregulated in response to abiotic stress. In addition, the subcellular localization assay showed that LhTRX-h3 was mainly distributed in the cytoplasm. Subsequently, we obtained LhTRX-h3 overexpression (OE) and knockout (KO) callus lines in Liriodendron hybrid. Compared to the wild type (WT) and LhTRX-h3-KO callus proliferation of LhTRX-h3-OE lines was significantly enhanced with reduced reactive oxygen species (ROS) accumulation under drought stress. Our findings that LhTRX-h3 is sufficient to improve drought tolerance. and underscore the significance of the TRX gene family in environmental stress responses in Liriodendron.

Regulatory mechanisms used by ZmMYB39 to enhance drought tolerance in maize (Zea mays) seedlings

Drought is a significant abiotic stressor that limits maize (Zea mays L.) growth and development. Thus, enhancing drought tolerance is critical for promoting maize production. Our findings demonstrated that ZmMYB39 is an MYB transcription factor with transcriptional activation activity. Drought stress experiments involving ZmMYB39 overexpression and knockout lines indicated that ZmMYB39 positively regulated drought stress tolerance in maize. DAP-Seq, EMSA, dual-LUC, and RT-qPCR provided initial insights into the molecular regulatory mechanisms by which ZmMYB39 enhances drought tolerance in maize. ZmMYB39 directly promoted the expression of ZmP5CS1, ZmPOX1, ZmSOD2, ZmRD22, ZmNAC49, and ZmDREB2A, which are involved in stress resistance. ZmMYB39 enhanced drought tolerance by interacting with and promoting the expression of ZmFNR1, ZmHSP20, and ZmDOF6. Our study offers a theoretical basis for understanding the molecular regulatory networks involved in maize drought stress response. Furthermore, ZmMYB39 serves as a valuable genetic resource for breeding drought-resistant maize.

Upland rice genomic signatures of adaptation to drought resistance and navigation to molecular design breeding

Upland rice is a distinctive drought-aerobic ecotype of cultivated rice highly resistant to drought stress. However, the genetic and genomic basis for the drought-aerobic adaptation of upland rice remains largely unclear due to the lack of genomic resources. In this study, we identified 25 typical upland rice accessions and assembled a high-quality genome of one of the typical upland rice varieties, IRAT109, comprising 384 Mb with a contig N50 of 19.6 Mb. Phylogenetic analysis revealed upland and lowland rice have distinct ecotype differentiation within the japonica subgroup. Comparative genomic analyses revealed that adaptive differentiation of lowland and upland rice is likely attributable to the natural variation of many genes in promoter regions, formation of specific genes in upland rice, and expansion of gene families. We revealed differentiated gene expression patterns in the leaves and roots of the two ecotypes and found that lignin synthesis mediated by the phenylpropane pathway plays an important role in the adaptive differentiation of upland and lowland rice. We identified 28 selective sweeps that occurred during domestication and validated that the qRT9 gene in selective regions can positively regulate drought resistance in rice. Eighty key genes closely associated with drought resistance were appraised for their appreciable potential in drought resistance breeding. Our study enhances the understanding of the adaptation of upland rice and provides a genome navigation map of drought resistance breeding, which will facilitate the breeding of drought-resistant rice and the "blue revolution" in agriculture.

Complex plant responses to drought and heat stress under climate change

Global climate change is predicted to result in increased yield losses of agricultural crops caused by environmental conditions. In particular, heat and drought stress are major factors that negatively affect plant development and reproduction, and previous studies have revealed how these stresses induce plant responses at physiological and molecular levels. Here, we provide a comprehensive overview of current knowledge concerning how drought, heat, and combinations of these stress conditions affect the status of plants, including crops, by affecting factors such as stomatal conductance, photosynthetic activity, cellular oxidative conditions, metabolomic profiles, and molecular signaling mechanisms. We further discuss stress-responsive regulatory factors such as transcription factors and signaling factors, which play critical roles in adaptation to both drought and heat stress conditions and potentially function as 'hubs' in drought and/or heat stress responses. Additionally, we present recent findings based on forward genetic approaches that reveal natural variations in agricultural crops that play critical roles in agricultural traits under drought and/or heat conditions. Finally, we provide an overview of the application of decades of study results to actual agricultural fields as a strategy to increase drought and/or heat stress tolerance. This review summarizes our current understanding of plant responses to drought, heat, and combinations of these stress conditions.

SNAC1-OsERF103-OsSDG705 module mediates drought response in rice

Drought stress profoundly hampers both plant growth and crop yield. To combat this, plants have evolved intricate transcriptional regulation mechanisms as a pivotal strategy. Through a genetic screening with rice genome-scale mutagenesis pool under drought stress, we identified an APETALA2/Ethylene Responsive Factor, namely OsERF103, positively responds to drought tolerance in rice. Combining chromatin immunoprecipitation sequencing and RNA sequencing analyses, we pinpointed c. 1000 genes directly influenced by OsERF103. Further results revealed that OsERF103 interacts with Stress-responsive NAC1 (SNAC1), a positive regulator of drought tolerance in rice, to synergistically regulate the expression of key drought-related genes, such as OsbZIP23. Moreover, we found that OsERF103 recruits a Su(var)3-9,enhancer of zeste and trithorax-domain group protein 705, which encodes a histone 3 lysine 4 (H3K4)-specific methyltransferase to specifically affect the deposition of H3K4me3 at loci like OsbZIP23 and other genes linked to dehydration responses. Additionally, the natural alleles of OsERF103 are selected during the domestication of both indica and japonica rice varieties and exhibit significant geographic distribution. Collectively, our findings have unfurled a comprehensive mechanistic framework underlying the OsERF103-mediated cascade regulation of drought response. This discovery not only enhances our understanding of drought signaling but also presents a promising avenue for the genetic improvement of drought-tolerant rice cultivars.

OsGEX3 affects anther development and improves osmotic stress tolerance in rice

MAIN CONCLUSION

Overexpression and loss of function of OsGEX3 reduce seed setting rates and affect pollen fertility in rice. OsGEX3 positively regulates osmotic stress response by regulating ROS scavenging. GEX3 proteins are conserved in plants. AtGEX3 encodes a plasma membrane protein that plays a crucial role in pollen tube guidance. However, the function of its homolog in rice, OsGEX3, has not been determined. Our results demonstrate that OsGEX3 is localized in the plasma membrane and the nucleus as shown by a transiently transformed assay using Nicotiana benthamiana leaves. The up-regulation of OsGEX3 was detected in response to treatments with polyethylene glycol (PEG) 4000, hydrogen peroxide, and abscisic acid (ABA) via RT-qPCR analysis. Interestingly, we observed a significant decline in the seed setting rates of OsGEX3-OE lines and mutants, compared to the wild type. Further investigations reveal that overexpression and loss of function of OsGEX3 affect pollen maturation. TEM observation revealed a significant decrease in the fertile pollen rates of OsGEX3-OE transgenic lines and Osgex3 mutants due to a delay in pollen development at the late vacuolated stage. Overexpression of OsGEX3 improved osmotic stress and oxidative stress tolerance by enhancing reactive oxygen species (ROS) scavenging in rice seedlings, whereas Osgex3 mutants exhibited an opposite phenotype in osmotic stress. These findings highlight the multifunctional roles of OsGEX3 in pollen development and the response to abiotic stress. The functional characterization of OsGEX3 provides a fundamental basis for rice molecular breeding and can facilitate efforts to cultivate drought resistance and yield-related varieties.

Analysis of the molecular mechanisms regulating how ZmEREB24 improves drought tolerance in maize (Zea mays) seedlings

Drought stress is one of the most limiting factors of maize productivity and can lead to a sharp reduction in the total biomass when it occurs at the seedling stage. Improving drought tolerance at the seedling stage is of great importance for maize breeding. The AP2/ERF transcription factor family plays a critical role in plant response to abiotic stresses. Here, we used a preliminary previously-generated ranscriptomic dataset to identify a highly drought-stress-responsive AP2 gene, i.e., ZmEREB24. Compared to the wild type, the overexpression of ZmEREB24 in maize significantly promotes drought tolerance of transgenic plants at the seedling stage. CRISPR/Cas9-based ZmEREB24-knockout mutants showed a drought-sensitive phenotype. RNA-seq analysis and EMSA assay revealed AATGG.CT and GTG.T.GCC motifs as the main binding sites of ZmEREB24 to the promoters of downstream target genes. DAP-seq identified four novel target genes involved in proline and sugar metabolism and hormone signal transduction of ZmEREB24. Our data indicate that ZmEREB24 plays important biological functions in regulating drought tolerance by binding to the promoters of drought stress genes and modulating their expression. The results further suggest a role of ZmEREB24 in regulating drought adaptation in maize, indicating its potential importance for employing molecular breeding in the development of high-yield drought-tolerant maize cultivars.

Molecular Mechanisms and Regulatory Pathways Underlying Drought Stress Response in Rice

Rice is a staple food for 350 million people globally. Its yield thus affects global food security. Drought is a serious environmental factor affecting rice growth. Alleviating the inhibition of drought stress is thus an urgent challenge that should be solved to enhance rice growth and yield. This review details the effects of drought on rice morphology, physiology, biochemistry, and the genes associated with drought stress response, their biological functions, and molecular regulatory pathways. The review further highlights the main future research directions to collectively provide theoretical support and reference for improving drought stress adaptation mechanisms and breeding new drought-resistant rice varieties.

Understanding AP2/ERF Transcription Factor Responses and Tolerance to Various Abiotic Stresses in Plants: A Comprehensive Review

Abiotic stress is an adverse environmental factor that severely affects plant growth and development, and plants have developed complex regulatory mechanisms to adapt to these unfavourable conditions through long-term evolution. In recent years, many transcription factor families of genes have been identified to regulate the ability of plants to respond to abiotic stresses. Among them, the AP2/ERF (APETALA2/ethylene responsive factor) family is a large class of plant-specific proteins that regulate plant response to abiotic stresses and can also play a role in regulating plant growth and development. This paper reviews the structural features and classification of AP2/ERF transcription factors that are involved in transcriptional regulation, reciprocal proteins, downstream genes, and hormone-dependent signalling and hormone-independent signalling pathways in response to abiotic stress. The AP2/ERF transcription factors can synergise with hormone signalling to form cross-regulatory networks in response to and tolerance of abiotic stresses. Many of the AP2/ERF transcription factors activate the expression of abiotic stress-responsive genes that are dependent or independent of abscisic acid and ethylene in response to abscisic acid and ethylene. In addition, the AP2/ERF transcription factors are involved in gibberellin, auxin, brassinosteroid, and cytokinin-mediated abiotic stress responses. The study of AP2/ERF transcription factors and interacting proteins, as well as the identification of their downstream target genes, can provide us with a more comprehensive understanding of the mechanism of plant action in response to abiotic stress, which can improve plants' ability to tolerate abiotic stress and provide a more theoretical basis for increasing plant yield under abiotic stress.

Advances in RNA Interference for Plant Functional Genomics: Unveiling Traits, Mechanisms, and Future Directions

RNA interference (RNAi) is a conserved molecular mechanism that plays a critical role in post-transcriptional gene silencing across diverse organisms. This review delves into the role of RNAi in plant functional genomics and its applications in crop improvement, highlighting its mechanistic insights and practical implications. The review begins with the foundational discovery of RNAi's mechanism, tracing its origins from petunias to its widespread presence in various organisms. Various classes of regulatory non-coding small RNAs, including siRNAs, miRNAs, and phasiRNAs, have been uncovered, expanding the scope of RNAi-mediated gene regulation beyond conventional understanding. These RNA classes participate in intricate post-transcriptional and epigenetic processes that influence gene expression. In the context of crop enhancement, RNAi has emerged as a powerful tool for understanding gene functions. It has proven effective in deciphering gene roles related to stress resistance, metabolic pathways, and more. Additionally, RNAi-based approaches hold promise for integrated pest management and sustainable agriculture, contributing to global efforts in food security. This review discusses RNAi's diverse applications, such as modifying plant architecture, extending shelf life, and enhancing nutritional content in crops. The challenges and future prospects of RNAi technology, including delivery methods and biosafety concerns, are also explored. The global landscape of RNAi research is highlighted, with significant contributions from regions such as China, Europe, and North America. In conclusion, RNAi remains a versatile and pivotal tool in modern plant research, offering novel avenues for understanding gene functions and improving crop traits. Its integration with other biotechnological approaches such as gene editing holds the potential to shape the future of agriculture and sustainable food production.

Genome-Wide Analysis of MYB Genes in Primulina eburnea (Hance) and Identification of Members in Response to Drought Stress

Due to periodic water deficiency in karst environments, Primulina eburnea experiences sporadic drought stress in its habitat. Despite being one of the largest gene families and functionally diverse in terms of plant growth and development, MYB transcription factors in P. eburnea have not been studied. Here, a total of 230 MYB genes were identified in P. eburnea, including 67 1R-MYB, 155 R2R3-MYB, six 3R-MYB, and two 4R-MYB genes. The R2R3-type PebMYB genes could be classified into 16 subgroups, while the remaining PebMYB genes (1R-MYB, 3R-MYB, and 4R-MYB genes) were divided into 10 subgroups. Notably, the results of the phylogenetic analysis were further supported by the motif and gene structure analysis, which showed that individuals in the same subgroup had comparable motif and structure organization. Additionally, gene duplication and synteny analyses were performed to better understand the evolution of PebMYB genes, and 291 pairs of segmental duplicated genes were found. Moreover, RNA-seq analysis revealed that the PebMYB genes could be divided into five groups based on their expression characteristics. Furthermore, 11 PebMYB genes that may be involved in drought stress response were identified through comparative analysis with Arabidopsis thaliana. Notably, seven of these genes (PebMYB3, PebMYB13, PebMYB17, PebMYB51, PebMYB142, PebMYB69, and PebMYB95) exhibited significant differences in expression between the control and drought stress treatments, suggesting that they may play important roles in drought stress response. These findings clarified the characteristics of the MYB gene family in P. eburnea, augmenting our comprehension of their potential roles in drought stress adaptation.

Comparative transcriptomic data confirm the findings of dehydration stress-induced redox biology of indigenous aromatic rice cultivars

The present work compares the transcriptome data sets of post-imbibitional dehydration stress-raised seedlings of two contrasting indigenous aromatic rice cultivars (Oryza sativa L., Cultivars Jamainadu and Badshabhog) for unfolding genetic regulation of dehydration stress. The result of RNA-seq analysis in Illumina platform in general revealed significant cultivar-specific expression of genes under dehydration stress that substantiate the data of redox metabolic fingerprints (assessed in terms of differential efficacy of ascorbate-glutathione pathway, ROS-antioxidant interaction dynamics and sensitive biomarkers of oxidative stress). Both the cultivars showed a diverse global transcriptomic response under water-deficit condition. Transcripts selected for heatmap generation with proper annotation revealed genes that are significantly expressed and mainly involved in redox functions, signaling, membrane trafficking, replication, protein synthesis, etc. Gene ontology (GO) analysis proposed that dehydration stress in the drought-tolerant cultivar Badshabhog was attributable to the enhanced expression of genes associated with carbon dioxide-concentrating mechanism, peroxysomal biogenesis, protein modification, protein synthesis, mitochondrial electron transport chain functioning, intercellular protein transport, histone demethylation associated with developmental process, regulation of apoptosis, etc. The redox genes that got significantly over-expressed in the IARC Badshabhog vis-à-vis Jamainadu include l-ascorbate oxidase/peroxidase, monothiol glutaredoxin-S1, thioredoxin-like protein AAED1 (chloroplastic), thioredoxin-like protein CXXS1, NADH-dehydrogenase (ubiquinone)-1-beta subcomplex subunit 3-B, NADH-dehydrogenase subunit 6 and K, lipoxygenase 6 isoform-XI, etc. Overall, the results of the RNA-seq analysis led to the identification of cultivar-specific genes, with the cultivar Badshabhog exhibiting significantly greater molecular reprogramming for redox regulation and signaling necessary for combating dehydration stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03829-z.

A comprehensive investigation of the regulatory roles of OsERF096, an AP2/ERF transcription factor, in rice cold stress response

KEY MESSAGE

OsERF096 negatively regulates rice cold tolerance and mediates IAA biosynthesis and signaling under cold stress. The APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors play important roles in regulating plant tolerance to abiotic stress. OsERF096 was previously identified as a direct target of miR1320, and was suggested to negatively regulate rice cold tolerance. In this study, we performed RNA-sequencing and targeted metabolomics assays to reveal the regulatory roles of OsERF096 in cold stress response. GO and KEGG analysis of differentially expressed genes showed that the starch and sucrose metabolism, plant-pathogen interaction, and plant hormone signal transduction pathways were significantly enriched. Quantification analysis confirmed a significant difference in sugar contents among WT and OsERF096 transgenic lines under cold treatment. Targeted metabolomics analysis uncovered that IAA accumulation and signaling were modified by OsERF096 in response to cold stress. Expectedly, qRT-PCR assays confirmed significant OsIAAs and OsARFs expression changes in OsERF096 transgenic lines. Finally, we identified three targets of OsERF096 based on RNA-seq, qRT-PCR, and dual-LUC assays. In summary, these results revealed the multiple regulatory roles of OsERF096 in cold stress response.

Natural variation in OsSEC13 HOMOLOG 1 modulates redox homeostasis to confer cold tolerance in rice

Rice (Oryza sativa L.) is a cold-sensitive species that often faces cold stress, which adversely affects yield productivity and quality. However, the genetic basis for low-temperature adaptation in rice remains unclear. Here, we demonstrate that 2 functional polymorphisms in O. sativa SEC13 Homolog 1 (OsSEH1), encoding a WD40-repeat nucleoporin, between the 2 subspecies O. sativa japonica and O. sativa indica rice, may have facilitated cold adaptation in japonica rice. We show that OsSEH1 of the japonica variety expressed in OsSEH1MSD plants (transgenic line overexpressing the OsSEH1 allele from Mangshuidao [MSD], cold-tolerant landrace) has a higher affinity for O. sativa metallothionein 2b (OsMT2b) than that of OsSEH1 of indica. This high affinity of OsSEH1MSD for OsMT2b results in inhibition of OsMT2b degradation, with decreased accumulation of reactive oxygen species and increased cold tolerance. Transcriptome analysis indicates that OsSEH1 positively regulates the expression of the genes encoding dehydration-responsive element-binding transcription factors, i.e. OsDREB1 genes, and induces the expression of multiple cold-regulated genes to enhance cold tolerance. Our findings highlight a breeding resource for improving cold tolerance in rice.

Molecular mechanisms of drought resistance using genome-wide association mapping in maize (Zea mays L.)

BACKGROUND

Drought is a critical abiotic stress that influences maize yield and reduces grain yield when it occurs at the flowering or filling stage. To dissect the genetic architecture of grain yield under drought stress (DS), a genome-wide association analysis was conducted in a maize population composed of diverse inbred lines from five locations under well-watered and DS conditions at flowering in 2019 and 2020.

RESULTS

Using a fixed and random model circulating probability unification model, a total of 147 loci associated with grain yield or the drought resistance index (DRI) were identified, of which 54 loci were associated with a DRI with an average phenotypic variation explanation of 4.03%. Further, 10 of these loci explained more than 10% of the phenotypic variation. By integrating two public transcriptome datasets, 22 differentially expressed genes were considered as candidate genes, including the cloned gene ZmNAC49, which responds to drought by regulating stomatal density. Enrichment and protein interaction network showed that signaling pathways responded to drought resistance, including jasmonic acid and salicylic acid, mitogen-activated protein kinase, and abscisic acid-activated. Additionally, several transcription factors involved in DS were identified, including basic leucine zipper (GRMZM2G370026), NAC (GRMZM2G347043), and ethylene-responsive element binding protein (GRMZM2G169654).

CONCLUSIONS

In this study, we nominated several genes as candidate genes for drought resistance by intergrating association maping and transcription analysis. These results provide valuable information for understanding the genetic basis of drought tolerance at the mature stage and for designing drought-tolerant maize breeding.

Genomic insights into selection for heterozygous alleles and woody traits in Populus tomentosa

Heterozygous alleles are widespread in outcrossing and clonally propagated woody plants. The variation in heterozygosity that underlies population adaptive evolution and phenotypic variation, however, remains largely unknown. Here, we describe a de novo chromosome-level genome assembly of Populus tomentosa, an economic and ecologically important native tree in northern China. By resequencing 302 natural accessions, we determined that the South subpopulation (Pop_S) encompasses the ancestral strains of P. tomentosa, while the Northwest subpopulation (Pop_NW) and Northeast subpopulation (Pop_NE) experienced different selection pressures during population evolution, resulting in significant population differentiation and a decrease in the extent of heterozygosity. Analysis of heterozygous selective sweep regions (HSSR) suggested that selection for lower heterozygosity contributed to the local adaptation of P. tomentosa by dwindling gene expression and genetic load in the Pop_NW and Pop_NE subpopulations. Genome-wide association studies (GWAS) revealed that 88 single nucleotide polymorphisms (SNPs) within 63 genes are associated with nine wood composition traits. Among them, the selection for the homozygous AA allele in PtoARF8 is associated with reductions in cellulose and hemicellulose contents by attenuating PtoARF8 expression, and the increase in lignin content is attributable to the selection for decreases in exon heterozygosity in PtoLOX3 during adaptive evolution of natural populations. This study provides novel insights into allelic variations in heterozygosity associated with adaptive evolution of P. tomentosa in response to the local environment and identifies a series of key genes for wood component traits, thereby facilitating genomic-based breeding of important traits in perennial woody plants.

Water Deficit at Vegetative Stage Induces Tolerance to High Temperature during Anthesis in Rice

BACKGROUND

Crop yields have been affected by many different biotic and abiotic factors. Generally, plants experience more than one stress during their life cycle, and plants can tolerate multiple stresses and develop cross-tolerance. The expected rise in atmospheric CO2 concentration ([CO2]) can contribute to cross-tolerance. Priming is a strategy to increase yield or to maintain yield under stress conditions. Thus, our objective was to evaluate if priming the rice plants with water deficit during the vegetative stage can induce tolerance to heat stress at anthesis and to evaluate the contribution of e[CO2].

METHODS

The experiment was arranged in a completely randomized design in a factorial arrangement. Factor A consisted of the following treatments: water deficit at four-leaf stage (no-stress, and drought stress), heat at anthesis (normal temperature, high temperature), and priming with water deficit at four-leaf stage and heat stress at anthesis; and Factor B was two [CO2] treatments: a[CO2] = 400 ± 40 μmol mol-1 and e[CO2] = 700 ± 40 μmol mol-1. We assessed the effect of the treatments on plant growth, yield, biochemical, and transcriptome alterations.

RESULTS

Although e[CO2] affected rice growth parameters, it did not affect the priming effect. Primed plants showed an increase in yield and number of panicles per plant. Primed plants showed upregulation of OsHSP16.9A, OsHSP70.1, and OsHSP70.6. These results showed induced cross-tolerance.

CONCLUSIONS

Water deficit at the rice vegetative stage reduces the effect of heat stress at the reproductive stage. Water deficit at the vegetative stage can be used, after further testing in field conditions, to reduce the effect of heat stress during flowering in rice.

Wheat ABA Receptor TaPYL5 Constitutes a Signaling Module with Its Downstream Partners TaPP2C53/TaSnRK2.1/TaABI1 to Modulate Plant Drought Response

Abscisic acid receptors (ABR) play crucial roles in transducing the ABA signaling initiated by osmotic stresses, which has a significant impact on plant acclimation to drought by modulating stress-related defensive physiological processes. We characterized TaPYL5, a member of the ABR family in wheat (Triticum aestivum), as a mediator of drought stress adaptation in plants. The signals derived from the fusion of TaPYL5-GFP suggest that the TaPYL5 protein was directed to various subcellular locations, namely stomata, plasma membrane, and nucleus. Drought stress significantly upregulated the TaPYL5 transcripts in roots and leaves. The biological roles of ABA and drought responsive cis-elements, specifically ABRE and recognition sites MYB, in mediating gene transcription under drought conditions were confirmed by histochemical GUS staining analysis for plants harbouring a truncated TaPYL5 promoter. Yeast two-hybrid and BiFC assays indicated that TaPYL5 interacted with TaPP2C53, a clade A member of phosphatase (PP2C), and the latter with TaSnRK2.1, a kinase member of the SnRK2 family, implying the formation of an ABA core signaling module TaPYL5/TaPP2C53/TaSnRK2.1. TaABI1, an ABA responsive transcription factor, proved to be a component of the ABA signaling pathway, as evidenced by its interaction with TaSnRK2.1. Transgene analysis of TaPYL5 and its module partners, as well as TaABI1, revealed that they have an effect on plant drought responses. TaPYL5 and TaSnRK2.1 positively regulated plant drought acclimation, whereas TaPP2C53 and TaABI1 negatively regulated it. This coincided with the osmotic stress-related physiology shown in their transgenic lines, such as stomata movement, osmolytes biosynthesis, and antioxidant enzyme function. TaPYL5 significantly altered the transcription of numerous genes involved in biological processes related to drought defense. Our findings suggest that TaPYL5 is one of the most important regulators in plant drought tolerance and a valuable target for engineering drought-tolerant cultivars in wheat.

Prospects for rice in 2050

A key to achieve the goals put forward in the UN's 2030 Agenda for Sustainable Development, it will need transformative change to our agrifood systems. We must mount to the global challenge to achieve food security in a sustainable manner in the context of climate change, population growth, urbanization, and depletion of natural resources. Rice is one of the major staple cereal crops that has contributed, is contributing, and will still contribute to the global food security. To date, rice yield has held pace with increasing demands, due to advances in both fundamental and biological studies, as well as genomic and molecular breeding practices. However, future rice production depends largely on the planting of resilient cultivars that can acclimate and adapt to changing environmental conditions. This Special Issue highlight with reviews and original research articles the exciting and growing field of rice-environment interactions that could benefit future rice breeding. We also outline open questions and propose future directions of 2050 rice research, calling for more attentions to develop environment-resilient rice especially hybrid rice, upland rice and perennial rice.

Variations in OsSPL10 confer drought tolerance by directly regulating OsNAC2 expression and ROS production in rice

Drought is a major factor restricting the production of rice (Oryza sativa L.). The identification of natural variants for drought stress-related genes is an important step toward developing genetically improved rice varieties. Here, we characterized a member of the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family, OsSPL10, as a transcription factor involved in the regulation of drought tolerance in rice. OsSPL10 appears to play a vital role in drought tolerance by controlling reactive oxygen species (ROS) production and stomatal movements. Haplotype and allele frequency analyses of OsSPL10 indicated that most upland rice and improved lowland rice varieties harbor the OsSPL10^Hap1 allele, whereas the OsSPL10^Hap2 allele was mainly present in lowland and landrace rice varieties. Importantly, we demonstrated that the varieties with the OsSPL10^Hap1 allele showed low expression levels of OsSPL10 and its downstream gene, OsNAC2, which decreases the expression of OsAP37 and increases the expression of OsCOX11, thus preventing ROS accumulation and programmed cell death (PCD). Furthermore, the knockdown or knockout of OsSPL10 induced fast stomatal closure and prevented water loss, thereby improving drought tolerance in rice. Based on these observations, we propose that OsSPL10 confers drought tolerance by regulating OsNAC2 expression and that OsSPL10^Hap1 could be a valuable haplotype for the genetic improvement of drought tolerance in rice.

Understanding the molecular mechanism of drought resistance in Shanlan upland rice by transcriptome and phenotype analyses

Rice (Oryza sativa L.) is an important grain crop worldwide, and drought has become an important factor restricting rice yield. As a unique rice germplasm in Hainan (China), Shanlan upland rice has rich genetic diversity and certain advantage for breeding water-saving and drought-resistance rice. 48 varieties, including 41 Shanlan upland rice, 3 upland rice, and 4 irrigated rice varieties was cultivated in soil pots. The drought resistance was assessed at the seedling stage using the stress coefficients of seven indicators, as the D value calculating from five principal components to rank the varieties. Five cultivars with strong, medium, and low resistance, were selected for transcriptome sequencing. The results of the GSEA analysis showed that free amino acid content increased through the redistribution of energy in Shanlan upland rice to cope with drought stress. In addition, we found that Os03g0623100 was significantly up-regulated under drought stress conditions in varieties with high drought resistance, as compared with low resistance cultivars. The Os03g0623100 was predicted to interact with LEA protein in the STRING database, which may contribute to maintaining the energy metabolisms to under stress conditions. This study provides a view of Shanlan upland rice as a drought-resistant germplasm resource, and a deeper understanding of the molecular mechanism of crop drought resistance.

Grapevine bZIP transcription factor bZIP45 regulates VvANN1 and confers drought tolerance in Arabidopsis

Drought is a severe environmental condition that restricts the vegetative growth and reduces the yield of grapevine (Vitis vinifera L.). However, the mechanisms underlying grapevine response and adaptation to drought stress remain unclear. In the present study, we characterized an ANNEXIN gene, VvANN1, which plays a positive role in the drought stress response. The results indicated that VvANN1 was significantly induced by osmotic stress. Expression of VvANN1 in Arabidopsis thaliana enhanced osmotic and drought tolerance through modulating the level of MDA, H₂O₂, and O₂ ^·- at the seedling stage, implying that VvANN1 might be involved in the process of ROS homeostasis under drought or osmotic stress conditions. Moreover, we used yeast one-hybridization and chromatin immunoprecipitation assays to show that VvbZIP45 could regulate VvANN1 expression by directly binding to the promoter region of VvANN1 in response to drought stress. We also generated transgenic Arabidopsis that constitutively expressed the VvbZIP45 gene (35S::VvbZIP45) and further produced VvANN1Pro::GUS/35S::VvbZIP45 Arabidopsis plants via crossing. The genetic analysis results subsequently indicated that VvbZIP45 could enhance GUS expression in vivo under drought stress. Our findings suggest that VvbZIP45 may modulate VvANN1 expression in response to drought stress and reduce the impact of drought on fruit quality and yield.

IPA1 improves drought tolerance by activating SNAC1 in rice

Drought is a major abiotic stress to rice (Oryza sativa) during growth. Ideal Plant Architecture (IPA1), the first cloned gene controlling the ideal plant type in rice, has been reported to function in both ideal rice plant architecture and biotic resistance. Here, we report that the IPA1/OsSPL14, encoding a transcriptional factor, positively regulates drought tolerance in rice. The IPA1 is constitutively expressed and regulated by H₂O₂, abscisic acid, NaCl and polyethylene glycol 6000 treatments in rice. Furthermore, the IPA1-knockout plants showed much greater accumulation of H₂O₂ as measured by 3,3'-diaminobenzidine staining in leaves compared with WT plants. Yeast one-hybrid, dual-luciferase and electrophoretic mobility shift assays indicated that the IPA1 directly activates the promoter of SNAC1. Expression of SNAC1 is significantly down-regulated in IPA1 knockout plants. Further investigation indicated that the IPA1 plays a positive role in drought-stress tolerance by inducing reactive oxygen species scavenging in rice. Together, these findings indicated that the IPA1 played important roles in drought tolerance by regulating SNAC1, thus activating the antioxidant system in rice.

Multi-omics approach reveals the contribution of OsSEH1 to rice cold tolerance

As low environmental temperature adversely affects the growth, development and geographical distribution, plants have evolved multiple mechanisms involving changing physiological and metabolic processes to adapt to cold stress. In this study, we revealed that nucleoporin-coding gene OsSEH1 was a positive regulator of cold stress in rice. Physiological assays showed that the activity of antioxidant enzymes showed a significant difference between osseh1 knock-out lines and wild type under cold stress. Metabolome analysis revealed that the contents of large-scale flavonoids serving as ROS scavengers were lower in osseh1 mutants compared with wild type under cold stress. Transcriptome analysis indicated that the DEGs between osseh1 knock-out lines and wild type plants were enriched in defense response, regulation of hormone levels and oxidation-reduction process. Integration of transcriptomic and metabolic profiling revealed that OsSEH1 plays a role in the oxidation-reduction process by coordinately regulating genes expression and metabolite accumulation involved in phenylpropanoid and flavonoid biosynthetic pathway. In addition, Exogenous ABA application assays indicated that osseh1 lines had hypersensitive phenotypes compared with wild type plants, suggesting that OsSEH1 may mediate cold tolerance by regulating ABA levels.

TaERF87 and TaAKS1 synergistically regulate TaP5CS1/TaP5CR1-mediated proline biosynthesis to enhance drought tolerance in wheat

Drought stress limits wheat production and threatens food security world-wide. While ethylene-responsive factors (ERFs) are known to regulate plant response to drought stress, the regulatory mechanisms responsible for a tolerant phenotype remain unclear. Here, we describe the positive regulatory role of TaERF87 in mediating wheat tolerance to drought stress. TaERF87 overexpression (OE) enhances drought tolerance, while silencing leads to drought sensitivity in wheat. RNA sequencing with biochemical assays revealed that TaERF87 activates the expression of the proline biosynthesis genes TaP5CS1 and TaP5CR1 via direct binding to GCC-box elements. Furthermore, proline accumulates to higher levels in TaERF87- and TaP5CS1-OE lines than that in wild-type plants under well-watered and drought stress conditions concomitantly with enhanced drought tolerance in these transgenic lines. Moreover, the interaction between TaERF87 and the bHLH transcription factor TaAKS1 synergistically enhances TaP5CS1 and TaP5CR1 transcriptional activation. TaAKS1 OE also increases wheat drought tolerance by promoting proline accumulation. Additionally, our findings verified that TaERF87 and TaAKS1 are targets of abscisic acid-responsive element binding factor 2 (TaABF2). Together, our study elucidates the mechanisms underlying a positive response to drought stress mediated by the TaABF2-TaERF87/TaAKS1-TaP5CS1/TaP5CR1 module, and identifies candidate genes for the development of elite drought-tolerant wheat varieties.

Overexpression of ZmDHN15 Enhances Cold Tolerance in Yeast and Arabidopsis

Maize (Zea mays L.) originates from the subtropical region and is a warm-loving crop affected by low-temperature stress. Dehydrin (DHN) protein, a member of the Group 2 LEA (late embryogenesis abundant proteins) family, plays an important role in plant abiotic stress. In this study, five maize DHN genes were screened based on the previous transcriptome sequencing data in our laboratory, and we performed sequence analysis and promoter analysis on these five DHN genes. The results showed that the promoter region has many cis-acting elements related to cold stress. The significantly upregulated ZmDHN15 gene has been further screened by expression pattern analysis. The subcellular localization results show that ZmDHN15 fusion protein is localized in the cytoplasm. To verify the role of ZmDHN15 in cold stress, we overexpressed ZmDHN15 in yeast and Arabidopsis. We found that the expression of ZmDHN15 can significantly improve the cold resistance of yeast. Under cold stress, ZmDHN15-overexpressing Arabidopsis showed lower MDA content, lower relative electrolyte leakage, and less ROS (reactive oxygen species) when compared to wild-type plants, as well as higher seed germination rate, seedling survival rate, and chlorophyll content. Furthermore, analysis of the expression patterns of ROS-associated marker genes and cold-response-related genes indicated that ZmDHN15 genes play an important role in the expression of these genes. In conclusion, the overexpression of the ZmDHN15 gene can effectively improve the tolerance to cold stress in yeast and Arabidopsis. This study is important for maize germplasm innovation and the genetic improvement of crops.

Natural variation of Alfin-like family affects seed size and drought tolerance in rice

The Alfin-like (AL) family is a group of small plant-specific transcriptional factors involved in abiotic stresses in dicotyledon. In an early study, we found an AL gene in rice that was associated with grain yield under drought stress. However, little information is known about the AL family in rice. In this study, AL genes in the rice genome were identified, and the OsAL proteins were found to locate in the nucleus and have no transcriptional self-activation activity. The expression of the OsALs was regulated by different environmental stimulations and plant hormones. Association and domestication analysis revealed that natural variation of most OsALs was significantly associated with yield traits, drought resistance and divergence in grain size in indica and japonica rice varieties. Hap1 of OsAL7.1 and Hap7 of OsAL11 were favorable haplotypes of seed weight and germination under osmotic stress. Furthermore, osal7.1 and osal11 mutants have larger seeds and are more sensitive to abscisic acid and mannitol during germination stage. Overexpressing of OsAL7.1 and OsAL11 in rice weakened the tolerance to drought in the adult stage. Thus, our work provides informative knowledge for exploring and harnessing haplotype diversity of OsALs to improve yield stability under drought stress.

Natural variation of DROT1 confers drought adaptation in upland rice

Upland rice is a distinct ecotype that grows in aerobic environments and tolerates drought stress. However, the genetic basis of its drought resistance is unclear. Here, using an integrative approach combining a genome-wide association study with analyses of introgression lines and transcriptomic profiles, we identify a gene, DROUGHT1 (DROT1), encoding a COBRA-like protein that confers drought resistance in rice. DROT1 is specifically expressed in vascular bundles and is directly repressed by ERF3 and activated by ERF71, both drought-responsive transcription factors. DROT1 improves drought resistance by adjusting cell wall structure by increasing cellulose content and maintaining cellulose crystallinity. A C-to-T single-nucleotide variation in the promoter increases DROT1 expression and drought resistance in upland rice. The potential elite haplotype of DROT1 in upland rice could originate in wild rice (O. rufipogon) and may be beneficial for breeding upland rice varieties.

Transcriptome analysis of response strategy in Hemerocallis fulva under drought stress

BACKGROUND

Hemerocallis fulva is an important ground cover plant widely used in urban greening. The analysis of the molecular mechanism underlying the drought response of H. fulva can lay a foundation for improving its adaptability and expanding its planting area.

OBJECTIVE

To reveal the drought response mechanisms of H. fulva, identify candidate unigenes associated with drought response, and lay a foundation for further unigenes functional study and drought resistance improvement of H. fulva via genetic engineering.

METHODS

RNA was isolated from H. fulva under different experimental conditions. De novo transcriptomic analysis of the samples was performed to screen drought response unigenes. The transcriptional changes of candidate drought response unigenes were verified by quantitative real-time PCR.

RESULTS

The differentially expressed unigenes and their functions were analyzed after H. fulva treated by PEG-simulated drought stress and rewatering. The candidate unigenes, associated with H. fulva drought response, were identified after transcriptome analysis. Then, the transcription level of drought response unigenes of H. fulva under different conditions was further verified. Abscisic acid, protein phosphorylation, sterol biosynthesis and ion transport were involved in drought response with quick restore in H. fulva. The response unigenes, involved in hormone (ABA, JA, CK and GA) signaling pathways, defense response, high light response, karrikin response and leaf shaping, can maintain at changed expression levels even after stress withdraw.

CONCLUSION

Hemerocallis fulva has unique drought response mechanism. Negative regulation mechanism may play more important roles in drought response of H. fulva. The analysis of candidate unigenes, associated with drought response, lays a foundation for further drought resistance improvement of H. fulva.

TaFDL2-1A confers drought stress tolerance by promoting ABA biosynthesis, ABA responses, and ROS scavenging in transgenic wheat

Plants have developed various protective mechanisms to survive drought stress. Previously, it was shown that a wheat bZIP transcription factor gene TaFD-Like2-1A (TaFDL2-1A) can confer drought tolerance in Arabidopsis. However, the biological functions related to drought stress tolerance of TaFDL2-1A in wheat (Triticum aestivum L.) remain unclear. In the present study, overexpression of TaFDL2-1A in the wheat cultivar Fielder improved drought resistance and conferred abscisic acid (ABA) hypersensitivity. Further analysis showed that overexpression of TaFDL2-1A increased the hypersensitivity of stomata to drought stress and endogenous ABA content under drought conditions. Genetic analysis and transcriptional regulation analysis indicated that TaFDL2-1A binds directly to the promoter fragments of TaRAB21s and TaNCED2s via ACGT core cis-elements, thereby activating their expression, leading to enhanced ABA responses and endogenous ABA accumulation. In addition, our results demonstrate that overexpression of TaFDL2-1A results in higher SOD and GPX activities in wheat under drought conditions by promoting the expression of TaSOD1 and TaGPx1-D, indicating enhanced reactive oxygen species (ROS) scavenging. These results imply that TaFDL2-1A positively regulates ABA biosynthesis, ABA responses, and ROS scavenging to improve drought stress tolerance in transgenic wheat. Our findings improve our understanding of the mechanisms that allow the wheat bZIP transcription factor to improve drought resistance and provide a useful reference gene for breeding programs to enhance drought resistance.

CRISPR/Cas-mediated editing of cis-regulatory elements for crop improvement

To improve future agricultural production, major technological advances are required to increase crop production and yield. Targeting the coding region of genes via the Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated Protein (CRISPR/Cas) system has been well established and has enabled the rapid generation of transgene-free plants, which can lead to crop improvement. The emergence of the CRISPR/Cas system has also enabled scientists to achieve cis-regulatory element (CRE) editing and, consequently, engineering endogenous critical CREs to modulate the expression of target genes. Recent genome-wide association studies have identified the domestication of natural CRE variants to regulate complex agronomic quantitative traits and have allowed for their engineering via the CRISPR/Cas system. Although engineering plant CREs can be advantageous to drive gene expression, there are still many limitations to its practical application. Here, we review the current progress in CRE editing and propose future strategies to effectively target CREs for transcriptional regulation for crop improvement.

A gain-of-function allele of a DREB transcription factor gene ameliorates drought tolerance in wheat

Drought is a major environmental factor limiting wheat production worldwide. However, the genetic components underlying wheat drought tolerance are largely unknown. Here, we identify a DREB transcription factor gene (TaDTG6-B) by genome-wide association study that is tightly associated with drought tolerance in wheat. Candidate gene association analysis revealed that a 26-bp deletion in the TaDTG6-B coding region induces a gain-of-function for TaDTG6-BDel574, which exhibits stronger transcriptional activation, protein interactions, and binding activity to dehydration-responsive elements (DRE)/CRT cis-elements than the TaDTG6-BIn574 encoded by the allele lacking the deletion, thus conferring greater drought tolerance in wheat seedlings harboring this variant. Knockdown of TaDTG6-BDel574 transcripts attenuated drought tolerance in transgenic wheat, whereas its overexpression resulted in enhanced drought tolerance without accompanying phenotypic abnormalities. Furthermore, the introgression of the TaDTG6-BDel574 elite allele into drought-sensitive cultivars improved their drought tolerance, thus providing a valuable genetic resource for wheat breeding. We also identified 268 putative target genes that are directly bound and transcriptionally regulated by TaDTG6-BDel574. Further analysis showed that TaDTG6-BDel574 positively regulates TaPIF1 transcription to enhance wheat drought tolerance. These results describe the genetic basis and accompanying mechanism driving phenotypic variation in wheat drought tolerance, and provide a novel genetic resource for crop breeding programs.

ZmLBD2 a maize (Zea mays L.) lateral organ boundaries domain (LBD) transcription factor enhances drought tolerance in transgenic Arabidopsis thaliana

Maize (Zea mays L.) is an annual gramineous herb and is among the world's most important crop species. Drought is the main factor contributing to maize yield reduction. The lateral organ boundaries domain (LBD) proteins belong to a class of higher-plant-specific transcription factors. LBD proteins usually include the highly conserved lateral organ boundaries (LOB) domains that play essential roles in plant growth and response to biotic stresses. However, few studies have addressed the biological functions of LBD genes associated with maize response to drought. Here we cloned the ZmLBD2 gene from maize and described its role in combating drought. Investigating ZmLBD2 subcellular localization, we show that it localizes to the cell nucleus and can specifically bind with inverted repeats of "GCGGCG". Under drought stress, Arabidopsis thaliana overexpressing ZmLBD2 performed better than the wild-type plants in terms of seed germination rates, root length, relative water content, fresh weight, chlorophyll content, proline content, and antioxidant enzyme content. Arabidopsis overexpressing ZmLBD2 contained less MDA, H₂O₂, and O 2 - than the wild-type plants. Our protein-protein interaction results indicate an interaction between the ZmLBD2 and ZmIAA5 genes. In conclusion, the ZmLBD2 gene positively regulates H₂O₂ homeostasis in plants, strengthening drought resistance.

Molecular Events of Rice AP2/ERF Transcription Factors

APETALA2/ethylene response factor (AP2/ERF) is widely found in the plant kingdom and plays crucial roles in transcriptional regulation and defense response of plant growth and development. Based on the research progress related to AP2/ERF genes, this paper focuses on the classification and structural features of AP2/ERF transcription factors, reviews the roles of rice AP2/ERF genes in the regulation of growth, development and stress responses, and discusses rice breeding potential and challenges. Taken together; studies of rice AP2/ERF genes may help to elucidate and enrich the multiple molecular mechanisms of how AP2/ERF genes regulate spikelet determinacy and floral organ development, flowering time, grain size and quality, embryogenesis, root development, hormone balance, nutrient use efficiency, and biotic and abiotic response processes. This will contribute to breeding excellent rice varieties with high yield and high resistance in a green, organic manner.

Crop Root Responses to Drought Stress: Molecular Mechanisms, Nutrient Regulations, and Interactions with Microorganisms in the Rhizosphere

Roots play important roles in determining crop development under drought. Under such conditions, the molecular mechanisms underlying key responses and interactions with the rhizosphere in crop roots remain limited compared with model species such as Arabidopsis. This article reviews the molecular mechanisms of the morphological, physiological, and metabolic responses to drought stress in typical crop roots, along with the regulation of soil nutrients and microorganisms to these responses. Firstly, we summarize how root growth and architecture are regulated by essential genes and metabolic processes under water-deficit conditions. Secondly, the functions of the fundamental plant hormone, abscisic acid, on regulating crop root growth under drought are highlighted. Moreover, we discuss how the responses of crop roots to altered water status are impacted by nutrients, and vice versa. Finally, this article explores current knowledge of the feedback between plant and soil microbial responses to drought and the manipulation of rhizosphere microbes for improving the resilience of crop production to water stress. Through these insights, we conclude that to gain a more comprehensive understanding of drought adaption mechanisms in crop roots, future studies should have a network view, linking key responses of roots with environmental factors.

Osa-miR1320 targets the ERF transcription factor OsERF096 to regulate cold tolerance via JA-mediated signaling

MicroRNAs play key roles in abiotic stress response. Rice (Oryza sativa L.) miR1320 is a species-specific miRNA that contributes to miR168-regulated immunity. However, it is still unknown whether miR1320 is involved in rice response to abiotic stress. In this study, we illustrated that the miR1320 precursor generated two mature miR1320s, miR1320-3p, and miR1320-5p, and they both displayed decreased expression under cold stress. Genetic evidence showed that miR1320 overexpression resulted in increased cold tolerance, while miR1320 knock down (KD) reduced cold tolerance. Furthermore, an APETALA2/ethylene-responsive factor (ERF) transcription factor OsERF096 was identified as a target of miR1320 via 5'-RACE and dual luciferase assays. OsERF096 expression was altered by miR1320 overexpression and KD and exhibited an opposite pattern to that of miR1320 in different tissues and under cold stress. Consistently, OsERF096 negatively regulated cold stress tolerance. Furthermore, we suggested that OsERF096 could bind to the GCC and DRE cis-elements and act as a transcriptional activator in the nucleus. Based on RNA-sequencing and targeted metabolomics assays, we found that OsERF096 modified hormone content and signaling pathways. Finally, phenotypic and reverse transcription-quantitative PCR assays showed that jasmonic acid (JA) methyl ester application recovered the cold-sensitive phenotype and JA-activated expression of three Dehydration Responsive Element Binding genes in the OsERF096-OE line. Taken together, our results strongly suggest that the miR1320-OsERF096 module regulates cold tolerance by repressing the JA-mediated cold signaling pathway.

The OsEIL1-OsERF115-target gene regulatory module controls grain size and weight in rice

Grain size is one of the essential determinants of rice yield. Our previous studies revealed that ethylene plays an important role in grain-size control; however, the precise mechanism remains to be determined. Here, we report that the ethylene response factor OsERF115 functions as a key downstream regulator for ethylene-mediated grain development. OsERF115 encodes an AP2/ERF-type transcriptional factor that is specifically expressed in young spikelets and developing caryopses. Overexpression of OsERF115 significantly increases grain length, width, thickness and weight by promoting longitudinal elongation and transverse division of spikelet hull cells, as well as enhancing grain-filling activity, whereas its knockout mutations lead to the opposite effects, suggesting that OsERF115 positively regulates grain size and weight. OsERF115 transcription is strongly induced by ethylene, and OsEIL1 directly binds to the promoter to activate its expression. OsERF115 acts as a transcriptional repressor to directly or indirectly modulate a set of grain-size genes during spikelet growth and endosperm development. Importantly, haplotype analysis reveals that the SNP variations in the EIN3-binding sites of OsERF115 promoter are significantly associated with the OsERF115 expression levels and grain weight, suggesting that natural variations in the OsERF115 promoter contribute to grain-size diversity. In addition, the OsERF115 orthologues are identified only in grass species, implying a conserved and unique role in the grain development of cereal crops. Our results provide insights into the molecular mechanism of ethylene-mediated grain-size control and a potential strategy based on the OsEIL1-OsERF115-target gene regulatory module for genetic improvement of rice yield.

Natural variation of HTH5 from wild rice, Oryza rufipogon Griff., is involved in conferring high-temperature tolerance at the heading stage

Global warming is a major abiotic stress factor, which limit rice production. Exploiting the genetic basis of the natural variation in heat resistance at different reproductive stages among diverse exotic Oryza germplasms can help breeding heat-resistant rice cultivars. Here, we identified a stable quantitative trait locus (QTL) for heat tolerance at the heading stage on chromosome 5 (qHTH5) in O. rufipogon Griff. The corresponding gene, HTH5, pertains to the pyridoxal phosphate-binding protein PLPBP (formerly called PROSC) family, which is predicted to encode pyridoxal phosphate homeostasis protein (PLPHP) localized to the mitochondrion. Overexpression of HTH5 increased the seed-setting rate of rice plants under heat stress at the heading stage, whereas suppression of HTH5 resulted in greater susceptibility to heat stress. Further investigation indicated that HTH5 reduces reactive oxygen species accumulation at high temperatures by increasing the heat-induced pyridoxal 5'-phosphate (PLP) content. Moreover, we found that two SNPs located in the HTH5 promoter region are involved with its expression level and associated with heat tolerance diversity. These findings suggest that the novel gene HTH5 might have great potential value for heightening rice tolerance to heat stress to the on-going threat of global warming.

The AP2/ERF GmERF113 Positively Regulates the Drought Response by Activating GmPR10-1 in Soybean

Ethylene response factors (ERFs) are involved in biotic and abiotic stress; however, the drought resistance mechanisms of many ERFs in soybeans have not been resolved. Previously, we proved that GmERF113 enhances resistance to the pathogen Phytophthora sojae in soybean. Here, we determined that GmERF113 is induced by 20% PEG-6000. Compared to the wild-type plants, soybean plants overexpressing GmERF113 (GmERF113-OE) displayed increased drought tolerance which was characterized by milder leaf wilting, less water loss from detached leaves, smaller stomatal aperture, lower Malondialdehyde (MDA) content, increased proline accumulation, and higher Superoxide dismutase (SOD) and Peroxidase (POD) activities under drought stress, whereas plants with GmERF113 silenced through RNA interference were the opposite. Chromatin immunoprecipitation and dual effector-reporter assays showed that GmERF113 binds to the GCC-box in the GmPR10-1 promoter, activating GmPR10-1 expression directly. Overexpressing GmPR10-1 improved drought resistance in the composite soybean plants with transgenic hairy roots. RNA-seq analysis revealed that GmERF113 downregulates abscisic acid 8′-hydroxylase 3 (GmABA8’-OH 3) and upregulates various drought-related genes. Overexpressing GmERF113 and GmPR10-1 increased the abscisic acid (ABA) content and reduced the expression of GmABA8’-OH3 in transgenic soybean plants and hairy roots, respectively. These results reveal that the GmERF113-GmPR10-1 pathway improves drought resistance and affects the ABA content in soybean, providing a theoretical basis for the molecular breeding of drought-tolerant soybean.

Natural variation MeMYB108 associated with tolerance to stress-induced leaf abscission linked to enhanced protection against reactive oxygen species in cassava

Natural variation of the MeMYB108 exon was associated with reactive oxygen scavengers led to alleviate leaf abscission under drought in cassava. The reactive oxygen scavengers play important roles in regulating the cassava (Manihot esculenta Crantz) leaf abscission induced by stresses. To date, the relationship between natural variations of MYB genes and reactive oxygen scavengers under drought in cassava genotypes remains unclear. Here, we reported the transcription factor MeMYB108 played an important role in regulating leaf abscission exposed to drought in cassava. The expression levels of MeMYB108 in abscission zones of cassava leaf pulvinus were higher in cassava genotype SC124, which were less easy to shed leaves under stress than cassava genotype SC8 when the leaf abscission induced by the same drought condition. Compared with wild type and interference expression plants, overexpression of MeMYB108 significantly reduced the drought-induced leaf abscission rate under drought. The consecutively 2-year analysis of reactive oxygen scavengers showed significant differences among different cassava genotypes under drought-induced leaf abscission, indicating the relevance between reactive oxygen scavengers and leaf abscission. Correlation analysis revealed the natural variation of the MeMYB108 exon was associated with reactive oxygen scavengers during drought-induced leaf abscission. Association analysis between pairwise LD of DNA polymorphism indicated the MeMYB108 allele enhanced the tolerance of cassava to drought-induced leaf abscission. Complementation transgenic lines containing the elite allele of MeMYB108 ^SC124 decreased the leaf abscission rate induced by drought conditions, demonstrating natural variation in MeMYB108 contributed to leaf abscission tolerance induced by drought in cassava. Further studies showed MeMYB108 played an active role in the tolerance of cassava to drought-induced leaf abscission by inducing scavenging of reactive oxygen species.

Membrane-bound transcription factor TaNTL1 positively regulates drought stress tolerance in transgenic Arabidopsis

Drought negatively affects plant growth and development to cause major yield losses in crops. Transcription factors (TFs) play important roles in abiotic stress response signaling in plant. However, the biological functions of membrane-bound transcription factors (MTFs) in abiotic stress have rarely been studied in wheat. In this study, we identified a homologue of the maize ZmNTL1 gene in wheat, which was designated as TaNTL1. TaNTL1 is a NAC family MTF (NTM1-like, NTL proteins) encoding 481 amino acid residues with a transmembrane motif at the C-terminal. Quantitative results and expression profile analysis showed that TaNTL1 could respond to drought. We demonstrated the transcriptional activity of TaNTL1 and that it could specifically bind to NAC recognition cis-acting elements (NACBS). The full-length TaNTL1 protein localized in the plasma membrane and TaNTL1 lacking the transmembrane motif (TaNTL1-ΔTM) localized in the nucleus. TaNTL1 was proteolytically activated by PEG6000 and abscisic acid (ABA). Phenotypic and physiological analyses showed that overexpression transgenic Arabidopsis exhibited enhanced drought resistance, which was greater with TaNTL1-ΔTM than TaNTL1. Transient silencing of TaNTL1 significantly reduced the resistance to drought stress in wheat. Germination by the TaNTL1 and TaNTL1-ΔTM transgenic Arabidopsis seeds was also hypersensitive to ABA. Most of the stress-related genes in transgenic plants were upregulated under drought conditions. These results suggest that MTF TaNTL1 is a positive regulator of drought and it may function by entering the nucleus through cleavage.

Drought Tolerance Strategies and Autophagy in Resilient Wheat Genotypes

Drought resiliency strategies combine developmental, physiological, cellular, and molecular mechanisms. Here, we compare drought responses in two resilient spring wheat (Triticum aestivum) genotypes: a well-studied drought-resilient Drysdale and a resilient genotype from the US Pacific North-West Hollis. While both genotypes utilize higher water use efficiency through the reduction of stomatal conductance, other mechanisms differ. First, Hollis deploys the drought escape mechanism to a greater extent than Drysdale by accelerating the flowering time and reducing root growth. Second, Drysdale uses physiological mechanisms such as non-photochemical quenching (NPQ) to dissipate the excess of harvested light energy and sustain higher F_v/F_m and ϕ_PSII, whereas Hollis maintains constant NPQ but lower F_v/F_m and ϕ_PSII values. Furthermore, more electron donors of the electron transport chain are in the oxidized state in Hollis than in Drysdale. Third, many ROS homeostasis parameters, including peroxisome abundance, transcription of peroxisome biogenesis genes PEX11 and CAT, catalase protein level, and enzymatic activity, are higher in Hollis than in Drysdale. Fourth, transcription of autophagy flux marker ATG8.4 is upregulated to a greater degree in Hollis than in Drysdale under drought, whereas relative ATG8 protein abundance under drought stress is lower in Hollis than in Drysdale. These data demonstrate the activation of autophagy in both genotypes and a greater autophagic flux in Hollis. In conclusion, wheat varieties utilize different drought tolerance mechanisms. Combining these mechanisms within one genotype offers a promising strategy to advance crop resiliency.

Salix myrtillacea Female Cuttings Performed Better Than Males under Nitrogen Deposition on Leaves and Drought Conditions

Drought and nitrogen (N) deposition are major threats to global forests under climate change. However, investigation into how dioecious woody species acclimate to drought and N deposition and how this is influenced by gender has, so far, been unexplored. We examined the phenotypic and physiological changes in Salix myrtillacea females and males under 60 d drought, and wet N deposition on leaves’ treatments. Drought inhibited their growth by limiting water acquisition, photosynthesis, and increasing oxidative stress, especially in males. However, females exhibited greater drought resistance than males due to their better water acquisition ability and instantaneous water use efficiency (WUEleaf), higher foliar abscisic acid (ABA) and auxin (IAA) levels and greater antioxidase activities. N deposition increased foliar ABA, H2O2 accumulation, and reduced N distribution to the leaves, causing restricted photosynthesis and aerial growth in males. Interestingly, N deposition improved biomass accumulation in both the genders under drought, with greater positive effects on drought-stressed males by increasing their radial growth and causing greater N distribution to the leaves, increased foliar IAA and reduced oxidative stress. Regardless, S. myrtillacea females still showed better growth and drought resistance than males under both drought and N deposition. The females’ superior performance indicated that they are more appropriate for forestation, thus supporting the dominant gender’s selection in the afforestation of unisexual S. myrtillacea in drought and severe N deposition regions.

ZmLBD5 Increases Drought Sensitivity by Suppressing ROS Accumulation in Arabidopsis

Drought stress is known to significantly limit crop growth and productivity. Lateral organ boundary domain (LBD) transcription factors-particularly class-I members-play essential roles in plant development and biotic stress. However, little information is available on class-II LBD genes related to abiotic stress in maize. Here, we cloned a maize class-II LBD transcription factor, ZmLBD5, and identified its function in drought stress. Transient expression, transactivation, and dimerization assays demonstrated that ZmLBD5 was localized in the nucleus, without transactivation, and could form a homodimer or heterodimer. Promoter analysis demonstrated that multiple drought-stress-related and ABA response cis-acting elements are present in the promoter region of ZmLBD5. Overexpression of ZmLBD5 in Arabidopsis promotes plant growth under normal conditions, and suppresses drought tolerance under drought conditions. Furthermore, the overexpression of ZmLBD5 increased the water loss rate, stomatal number, and stomatal apertures. DAB and NBT staining demonstrated that the reactive oxygen species (ROS) decreased in ZmLBD5-overexpressed Arabidopsis. A physiological index assay also revealed that SOD and POD activities in ZmLBD5-overexpressed Arabidopsis were higher than those in wild-type Arabidopsis. These results revealed the role of ZmLBD5 in drought stress by regulating ROS levels.

The wheat ABA receptor gene TaPYL1-1B contributes to drought tolerance and grain yield by increasing water-use efficiency

The role of abscisic acid (ABA) receptors, PYR1/PYL/RCAR (PYLs), is well established in ABA signalling and plant drought response, but limited research has explored the regulation of wheat PYLs in this process, especially the effects of their allelic variations on drought tolerance or grain yield. Here, we found that the overexpression of a TaABFs-regulated PYL gene, TaPYL1-1B, exhibited higher ABA sensitivity, photosynthetic capacity and water-use efficiency (WUE), all contributed to higher drought tolerance than that of wild-type plants. This heightened water-saving mechanism further increased grain yield and protected productivity during water deficit. Candidate gene association analysis revealed that a favourable allele TaPYL1-1B^In-442 , carrying an MYB recognition site insertion in the promoter, is targeted by TaMYB70 and confers enhanced expression of TaPYL1-1B in drought-tolerant genotypes. More importantly, an increase in frequency of the TaPYL1-1B^In-442 allele over decades among modern Chinese cultivars and its association with high thousand-kernel weight together demonstrated that it was artificially selected during wheat improvement efforts. Taken together, our findings illuminate the role of TaPYL1-1B plays in coordinating drought tolerance and grain yield. In particular, the allelic variant TaPYL1-1B^In-442 substantially contributes to enhanced drought tolerance while maintaining high yield, and thus represents a valuable genetic target for engineering drought-tolerant wheat germplasm.

The co-modulation of RAV transcription factors in ROS burst and extensive transcriptional reprogramming underlies disease resistance in cassava

MeRAVs positively regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam. Cassava (Manihot esculenta Crantz) is an important food crop and energy crop, but its yield is seriously affected by cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam). Related to ABI3/VP1 (RAV) transcription factor family belongs to the APETALA2/Ethylene-Responsive Factor (AP2/ERF) family, which plays an important role in plant growth, development and response to biotic and abiotic stresses. In this study, we found that MeRAVs positively co-regulates the resistance to Xam and stimulates the innate immune response by regulating reactive oxygen species (ROS) burst in cassava. Dual-luciferase assay showed that seven MeRAVs exhibited transcriptional activate activity by binding CAACA motif and CACCTG motif. A large number of differentially expressed genes (DEGs) were identified through RNA-seq analysis of MeRAVs-silenced lines, and the DEGs co-regulated by seven MeRAVs accounted for more than 45% of the total DEGs. In addition, seven MeRAVs positively regulate expression of disease resistance-related genes through directly binding to their promoters. In summary, MeRAVs co-regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam.

Physio-biochemical responses and expressional profiling analysis of drought tolerant genes in new promising rice genotype

Rice cultivation in Egypt is limited by the scarcity of water resources. The main strategy of rice breeders to overcome this problem is to develop new high-yielding varieties that are tolerant to drought stress. In this study, an drought-tolerant (IR60080-46A) variety was crossed with commercial Egyptian varieties using the back-cross method and marker-assisted selection (MAS) approach. The advanced lines of these crosses were selected under drought stress conditions. The best-performing candidate line, RBL-112, and its parental genotypes, were evaluated under drought stress and control conditions. The RBL-112 line showed superior its root system, which in turn produced higher grain yield under drought-stress conditions than its parental and check genotypes. Furthermore, physiological and biochemical studies showed that the RBL-112 line maintained higher relative water content (RWC), maximum quantum efficiency of photosystem II (Fv/Fm) values, proline content, superoxide dismutase (SOD) activity, and lower malondialdehyde (MDA) content compared to its parents and the check. The functional expression profiles of 22 drought tolerance-related genes were studied, out of which the genes OsAHL1, OsLEA3, OsCATA, OsP5CS, OsSNAC1, Os1g64660, OsRab21, OsAPX2, OsDREB2A, OsSKIPa, and OsLG3 were strongly induced in the newly developed RBL-112 line under drought-stress conditions. It could be concluded that the new line has a higher capacity to modulate physiological activities and expression levels of several drought-induced genes to withstand drought stress with high yielding ability. This finding suggests that the RBL-112 line presents a promising new addition to enable sustainable rice cultivation under water-limited conditions, and confirms the efficiency of the approach implemented in the current study.