Down‐regulation of CBP80 gene expression as a strategy to engineer a drought‐tolerant potato

Developing new strategies for crop plants to respond to drought is crucial for their innovative breeding. The down‐regulation of nuclear cap‐binding proteins in Arabidopsis renders plants drought tolerant. The CBP80 gene in the potato cultivar Desiree was silenced using artificial microRNAs. Transgenic plants displayed a higher tolerance to drought, ABA‐hypersensitive stomatal closing, an increase in leaf stomata and trichome density, and compact cuticle structures with a lower number of microchannels. These findings were correlated with a higher tolerance to water stress. The level of miR159 was decreased, and the levels of its target mRNAs MYB33 and MYB101 increased in the transgenic plants subjected to drought. Similar trends were observed in an Arabidopsis cbp80 mutant. The evolutionary conservation of CBP80, a gene that plays a role in the response to drought, suggests that it is a candidate for genetic manipulations that aim to obtain improved water‐deficit tolerance of crop plants.     

Overexpression of ubiquitin‐like LpHUB1 gene confers drought tolerance in perennial ryegrass

HUB1, also known as Ubl5, is a member of the subfamily of ubiquitin‐like post‐translational modifiers. HUB1 exerts its role by conjugating with protein targets. The function of this protein has not been studied in plants. A HUB1 gene, LpHUB1, was identified from serial analysis of gene expression data and cloned from perennial ryegrass. The expression of this gene was reported previously to be elevated in pastures during the summer and by drought stress in climate‐controlled growth chambers. Here, pasture‐type and turf‐type transgenic perennial ryegrass plants overexpressing LpHUB1 showed improved drought tolerance, as evidenced by improved turf quality, maintenance of turgor and increased growth. Additional analyses revealed that the transgenic plants generally displayed higher relative water content, leaf water potential, and chlorophyll content and increased photosynthetic rate when subjected to drought stress. These results suggest HUB1 may play an important role in the tolerance of perennial ryegrass to abiotic stresses.     

OsASR5 enhances drought tolerance through a stomatal closure pathway associated with ABA and H2O2 signalling in rice

Drought is one of the major abiotic stresses that directly implicate plant growth and crop productivity. Although many genes in response to drought stress have been identified, genetic improvement to drought resistance especially in food crops is showing relatively slow progress worldwide. Here, we reported the isolation of abscisic acid, stress and ripening (ASR) genes from upland rice variety, IRAT109 (Oryza sativa L. ssp. japonica), and demonstrated that overexpression of OsASR5 enhanced osmotic tolerance in Escherichia coli and drought tolerance in Arabidopsis and rice by regulating leaf water status under drought stress conditions. Moreover, overexpression of OsASR5 in rice increased endogenous ABA level and showed hypersensitive to exogenous ABA treatment at both germination and postgermination stages. The production of H₂O₂, a second messenger for the induction of stomatal closure in response to ABA, was activated in overexpression plants under drought stress conditions, consequently, increased stomatal closure and decreased stomatal conductance. In contrast, the loss‐of‐function mutant, osasr5, showed sensitivity to drought stress with lower relative water content under drought stress conditions. Further studies demonstrated that OsASR5 functioned as chaperone‐like protein and interacted with stress‐related HSP40 and 2OG‐Fe (II) oxygenase domain containing proteins in yeast and plants. Taken together, we suggest that OsASR5 plays multiple roles in response to drought stress by regulating ABA biosynthesis, promoting stomatal closure, as well as acting as chaperone‐like protein that possibly prevents drought stress‐related proteins from inactivation.     

Improving plant drought tolerance and growth under water limitation through combinatorial engineering of signalling networks

Agriculture is by far the biggest water consumer on our planet, accounting for 70 per cent of all freshwater withdrawals. Climate change and a growing world population increase pressure on agriculture to use water more efficiently (‘more crop per drop’). Water‐use efficiency (WUE) and drought tolerance of crops are complex traits that are determined by many physiological processes whose interplay is not well understood. Here, we describe a combinatorial engineering approach to optimize signalling networks involved in the control of stress tolerance. Screening a large population of combinatorially transformed plant lines, we identified a combination of calcium‐dependent protein kinase genes that confers enhanced drought stress tolerance and improved growth under water‐limiting conditions. Targeted introduction of this gene combination into plants increased plant survival under drought and enhanced growth under water‐limited conditions. Our work provides an efficient strategy for engineering complex signalling networks to improve plant performance under adverse environmental conditions, which does not depend on prior understanding of network function.     

Expression of an Arabidopsis molybdenum cofactor sulphurase gene in soybean enhances drought tolerance and increases yield under field conditions

LOS5/ABA3 gene encoding molybdenum cofactor sulphurase is involved in aldehyde oxidase (AO) activity in Arabidopsis, which indirectly regulates ABA biosynthesis and increased stress tolerance. Here, we used a constitutive super promoter to drive LOS5/ABA3 overexpression in soybean (Glycine max L.) to enhance drought tolerance in growth chamber and field conditions. Expression of LOS5/ABA3 was up‐regulated by drought stress, which led to increasing AO activity and then a notable increase in ABA accumulation. Transgenic soybean under drought stress had reduced water loss by decreased stomatal aperture size and transpiration rate, which alleviated leaf wilting and maintained higher relative water content. Exposed to drought stress, transgenic soybean exhibited reduced cell membrane damage by reducing electrolyte leakage and production of malondialdehyde and promoting proline accumulation and antioxidant enzyme activities. Also, overexpression of LOS5/ABA3 enhanced expression of stress‐up‐regulated genes. Furthermore, the seed yield of transgenic plants is at least 21% higher than that of wide‐type plants under drought stress conditions in the field. These data suggest that overexpression of LOS5/ABA3 could improve drought tolerance in transgenic soybean via enhanced ABA accumulation, which could activate expression of stress‐up‐regulated genes and cause a series of physiological and biochemical resistant responses.     

Ectopic expression of a cyanobacterial flavodoxin in creeping bentgrass impacts plant development and confers broad abiotic stress tolerance

Flavodoxin (Fld) plays a pivotal role in photosynthetic microorganisms as an alternative electron carrier flavoprotein under adverse environmental conditions. Cyanobacterial Fld has been demonstrated to be able to substitute ferredoxin of higher plants in most electron transfer processes under stressful conditions. We have explored the potential of Fld for use in improving plant stress response in creeping bentgrass (Agrostis stolonifera L.). Overexpression of Fld altered plant growth and development. Most significantly, transgenic plants exhibited drastically enhanced performance under oxidative, drought and heat stress as well as nitrogen (N) starvation, which was associated with higher water retention and cell membrane integrity than wild‐type controls, modified expression of heat‐shock protein genes, production of more reduced thioredoxin, elevated N accumulation and total chlorophyll content as well as up‐regulated expression of nitrite reductase and N transporter genes. Further analysis revealed that the expression of other stress‐related genes was also impacted in Fld‐expressing transgenics. Our data establish a key role of Fld in modulating plant growth and development and plant response to multiple sources of adverse environmental conditions in crop species. This demonstrates the feasibility of manipulating Fld in crop species for genetic engineering of plant stress tolerance.     

Drought‐inducible changes in the histone modification H3K9ac are associated with drought‐responsive gene expression in Brachypodium distachyon

• H3K9ac, an epigenetic marker, is widely distributed in plant genomes. H3K9ac enhances gene expression, which is highly conserved in eukaryotes. However, genome‐wide studies of H3K9ac in monocot species are limited, and the changes in H3K9ac under drought stress for individual genes are still not clear.
• We analysed changes in the H3K9ac level of Brachypodium distachyon under 20% PEG‐6000‐simulated drought stress conditions. We also performed chromatin immunoprecipitation, followed by next generation sequencing (ChIP‐seq) on H3K9ac to reveal changes in H3K9ac for individual genes at the genome‐wide level.
• Our study showed that H3K9ac was mainly enriched in gene exon regions. Drought increased or decreased the H3K9ac level at specific genomic loci. We identified 40 genes associated with increased H3K9ac levels and 36 genes associated with decreased H3K9ac levels under drought stress. Further, RT‐qPCR analyses showed that H3K9ac was positively associated with gene expression of those drought‐responsive genes.
• We conclude that H3K9ac enhances the expression level of a large number of drought‐responsive genes under drought stress in B. distachyon. The data presented here will help to reveal the correlation of some specific drought‐responsive genes and their enriched H3K9ac levels in the model plant B. distachyon.

     

Overexpression of the leucine‐rich receptor‐like kinase gene LRK2 increases drought tolerance and tiller number in rice

Drought represents a key limiting factor of global crop distribution. Receptor‐like kinases play major roles in plant development and defence responses against stresses such as drought. In this study, LRK2, which encodes a leucine‐rich receptor‐like kinase, was cloned and characterized and found to be localized on the plasma membrane in rice. Promoter–GUS analysis revealed strong expression in tiller buds, roots, nodes and anthers. Transgenic plants overexpressing LRK2 exhibited enhanced tolerance to drought stress due to an increased number of lateral roots compared with the wild type at the vegetative stage. Moreover, ectopic expression of LRK2 seedlings resulted in increased tiller development. Yeast two‐hybrid screening and bimolecular fluorescence complementation (BiFC) indicated a possible interaction between LRK2 and elongation factor 1 alpha (OsEF1A) in vitro. These results suggest that LRK2 functions as a positive regulator of the drought stress response and tiller development via increased branch development in rice. These findings will aid our understanding of branch regulation in other grasses and support improvements in rice genetics.     

二氧化硫增强拟南芥植株对干旱的适应性

以模式植物拟南芥为材料,研究SO_2对植物干旱适应性的影响。采用分光光度法检测植物干旱生理指标的变化,并用半定量RT-PCR技术分析了拟南芥热激基因和干旱响应基因的转录水平。研究发现:4周龄拟南芥植株暴露于30mg/m3的SO_2后,6—72h间叶面气孔开度显著低于对照并逐渐减小,在暴露48h和72h时,热激转录因子HsfA2和热激基因Hsp17.7、Hsp17.6B、Hsp17.6C转录上调,干旱响应基因DREB2A、DREB2B和RD29A表达增强;在SO_2熏气72h后进行干旱胁迫,干旱期间SO_2预暴露植株的叶片相对含水量高于非熏气干旱处理组,植株萎蔫程度比后者明显减轻,且SO_2预暴露植株的地上组织中可溶性糖和脯氨酸含量升高,超氧化物歧化酶活性提高,丙二醛含量降低。结果表明:SO_2能降低气孔开度、提高抗氧化能力、上调热激基因和干旱响应基因转录,并能促进干旱期间植物细胞内渗透调节物质的合成和积累,促使抗氧化酶活性提高,从而降低干旱胁迫对植株造成的氧化损伤,增强拟南芥对干旱的适应性。植物通过基因转录应答、酶活性改变、渗透调节物质积累等,在适应环境高浓度SO_2的同时,提高了对干旱的适应性。     

A novel wheat α‐amylase inhibitor gene,TaHPS, significantly improves the salt and drought tolerance of transgenic Arabidopsis

On the basis of microarray analyses of the salt‐tolerant wheat mutant RH8706‐49, a previously unreported salt‐induced gene, designated as TaHPS [Triticum aestivum hypothetical (HPS)‐like protein], was cloned. Real‐time quantitative polymerase chain reaction analyses showed that expression of the gene was induced by abscisic acid, salt and drought. The encoded protein was found to be localized mainly in the plasma membranes. Transgenic Arabidopsis plants overexpressing TaHPS were more tolerant to salt and drought stresses than non‐transgenic wild‐type (WT) plants. Under salt stress, the root cells of the transgenic plants secreted more Na⁺ and guard cells took up more Ca²⁺ ions. Compared with wild‐type plants, TaHPS‐expressing transgenic plants showed significantly lower amylase activity and glucose and malic acid levels. Our results showed that the expression of TaHPS inhibited amylase activity, which subsequently led to a closure of stomatal apertures and thus improved plant tolerance to salt and drought.