Overexpression Levels of LbDREB6 Differentially Affect Growth, Drought, and Disease Tolerance in Poplar

Ectopic Expression of Distinct PLC Genes Identifies 'Compactness' as a Possible Architectural Shoot Strategy to Cope with Drought Stress

Phospholipase C (PLC) has been implicated in several stress responses, including drought. Overexpression (OE) of PLC has been shown to improve drought tolerance in various plant species. Arabidopsis contains nine PLC genes, which are subdivided into four clades. Earlier, OE of PLC3, PLC5 or PLC7 was found to increase Arabidopsis' drought tolerance. Here, we confirm this for three other PLCs: PLC2, the only constitutively expressed AtPLC; PLC4, reported to have reduced salt tolerance and PLC9, of which the encoded enzyme was presumed to be catalytically inactive. To compare each PLC and to discover any other potential phenotype, two independent OE lines of six AtPLC genes, representing all four clades, were simultaneously monitored with the GROWSCREEN-FLUORO phenotyping platform, under both control- and mild-drought conditions. To investigate which tissues were most relevant to achieving drought survival, we additionally expressed AtPLC5 using 13 different cell- or tissue-specific promoters. While no significant differences in plant size, biomass or photosynthesis were found between PLC lines and wild-type (WT) plants, all PLC-OE lines, as well as those tissue-specific lines that promoted drought survival, exhibited a stronger decrease in 'convex hull perimeter' (= increase in 'compactness') under water deprivation compared to WT. Increased compactness has not been associated with drought or decreased water loss before although a hyponastic decrease in compactness in response to increased temperatures has been associated with water loss. We propose that the increased compactness could lead to decreased water loss and potentially provide a new breeding trait to select for drought tolerance.

RtNAC055 promotes drought tolerance via a stomatal closure pathway linked to methyl jasmonate/hydrogen peroxide signaling in Reaumuria trigyna

The stomata regulate CO2 uptake and efficient water usage, thereby promoting drought stress tolerance. NAC proteins (NAM, ATAF1/2, and CUC2) participate in plant reactions following drought stress, but the molecular mechanisms underlying NAC-mediated regulation of stomatal movement are unclear. In this study, a novel NAC gene from Reaumuria trigyna, RtNAC055, was found to enhance drought tolerance via a stomatal closure pathway. It was regulated by RtMYC2 and integrated with jasmonic acid signaling and was predominantly expressed in stomata and root. The suppression of RtNAC055 could improve jasmonic acid and H2O2 production and increase the drought tolerance of transgenic R. trigyna callus. Ectopic expression of RtNAC055 in the Arabidopsis atnac055 mutant rescued its drought-sensitive phenotype by decreasing stomatal aperture. Under drought stress, overexpression of RtNAC055 in poplar promoted ROS (H2O2) accumulation in stomata, which accelerated stomatal closure and maintained a high photosynthetic rate. Drought upregulated the expression of PtRbohD/F, PtP5CS2, and PtDREB1.1, as well as antioxidant enzyme activities in heterologous expression poplars. RtNAC055 promoted H2O2 production in guard cells by directly binding to the promoter of RtRbohE, thus regulating stomatal closure. The stress-related genes RtDREB1.1/P5CS1 were directly regulated by RtNAC055. These results indicate that RtNAC055 regulates stomatal closure by maintaining the balance between the antioxidant system and H2O2 level, reducing the transpiration rate and water loss, and improving photosynthetic efficiency and drought resistance.

Root transcriptomic provides insights on molecular mechanisms involved in the tolerance to water deficit in Pisum sativum inoculated with Pseudomonas sp

MAIN CONCLUSION

Root transcriptomics and biochemical analyses in water-stressed Pisum sativum plants inoculated with Pseudomonas spp. suggested preservation of ABA-related pathway and ROS detoxification, resulting in an improved tolerance to stress. Drought already affects agriculture in large areas of the globe and, due to climate change, these areas are predicted to become increasingly unsuitable for agriculture. For several years, plant growth-promoting bacteria (PGPB) have been used to improve legume yields, but many aspects of this interaction are still unclear. To elucidate the mechanisms through which root-associated PGPB can promote plant growth in dry environments, we investigated the response of pea plants inoculated with a potentially beneficial Pseudomonas strain (PK6) and subjected to two different water regimes. Combined biometric, biochemical, and root RNA-seq analyses revealed that PK6 improved pea growth specifically under water deficit, as inoculated plants showed an increased biomass, larger leaves, and longer roots. Abscisic acid (ABA) and proline quantification, together with the transcriptome analysis, suggested that PK6-inoculated plant response to water deficit was more diversified compared to non-inoculated plants, involving alternative metabolic pathways for the detoxification of reactive oxygen species (ROS) and the preservation of the ABA stress signaling pathway. We suggest that the metabolic response of PK6-inoculated plants was more effective in their adaptation to water deprivation, leading to their improved biometric traits. Besides confirming the positive role that PGPB can have in the growth of a legume crop under adverse conditions, this study offers novel information on the mechanisms regulating plant-bacteria interaction under varying water availability. These mechanisms and the involved genes could be exploited in the future for the development of legume varieties, which can profitably grow in dry climates.

Silencing a dehydration-responsive element-binding gene enhances the resistance of plants to a phloem-feeding herbivore

Herbivore-induced plant defence responses share common components with plant responses to abiotic stresses. However, whether abiotic stress-responsive factors influence the resistance of plants to herbivores by regulating these components remains largely unknown. Here, we cloned a dehydration-responsive element-binding gene in rice, OsDREB1A, and investigated its role in the resistance of rice to the phloem-feeding herbivore, brown planthopper (BPH, Nilaparvata lugens), under normal and low temperatures. We found that OsDREB1A localized to the nucleus, and its transcripts in rice were up-regulated in response to BPH infestation, low temperatures and treatment with methyl jasmonate or salicylic acid. Silencing OsDREB1A changed transcript levels of two defence-related WRKY and two PLD genes, enhanced levels of jasmonic acid (JA), JA-isoleucine and abscisic acid, and decreased the ethylene level in rice; these changes subsequently enhanced the resistance of plants to BPH, especially at 17°C, by decreasing the hatching rate and delaying the development of BPH eggs. Moreover, silencing OsDREB1A increased the growth of rice plants. These findings suggest that OsDREB1A, which positively regulates the resistance of rice to abiotic stresses, negatively regulates the resistance of rice to BPH.

Genome-wide identification and expression analysis of the Pisum sativum (L.) APETALA2/ethylene-responsive factor (AP2/ERF) gene family reveals functions in drought and cold stresses

AP2/ERF (APETALA2/Ethylene Response Factor) is a family of transcription factors that play essential roles in regulating gene expression in response to various environmental stimuli, including biotic and abiotic stresses, hormone signaling, and developmental processes. Pisum sativum (L.), commonly known as garden pea, is a winter crop sensitive to high temperatures and can also be affected by extreme cold and drought conditions. This study performed a genome-wide analysis of AP2/ERF genes and identified 153 AP2/ERF genes in P. sativum. Based on the conserved AP2/ERF domain and sequence homology, they were classified into AP2 (APETALA2), ERF (Ethylene Response Factor), DREB (Dehydration responsive element-binding), RAV (Related to Abscisic Acid Insensitive 3/ Viviparous 1) and Soloist subfamily. The DREB and ERF subfamily were further divided into groups A1-6 and B1-B6. Tandem and segmental duplication events were more frequent in the ERF subfamily, which can have important implications for their evolution and functional diversification. Under cold stress, the expression of DREB1A was highly induced in leaves, whereas DREB1B was suppressed. Similarly, the DREB2A, DREB2C, DREB2E, and DREB2F were induced in leaves under drought stress. The putative target genes of AP2/ERF transcription factors are highly diversified, suggesting that they play essential roles in various physiological responses in plants, including responses to biotic and abiotic stresses as well as developmental processes. Thus, this study of AP2/ERF genes and their functions provides valuable insight into how P. sativum responds to different environmental conditions, including cold and drought stresses.

Stimulation of Tomato Drought Tolerance by PHYTOCHROME A and B1B2 Mutations

Drought stress is a severe environmental issue that threatens agriculture at a large scale. PHYTOCHROMES (PHYs) are important photoreceptors in plants that control plant growth and development and are involved in plant stress response. The aim of this study was to identify the role of PHYs in the tomato cv. 'Moneymaker' under drought conditions. The tomato genome contains five PHYs, among which mutant lines in tomato PHYA and PHYB (B1 and B2) were used. Compared to the WT, phyA and phyB1B2 mutants exhibited drought tolerance and showed inhibition of electrolyte leakage and malondialdehyde accumulation, indicating decreased membrane damage in the leaves. Both phy mutants also inhibited oxidative damage by enhancing the expression of reactive oxygen species (ROS) scavenger genes, inhibiting hydrogen peroxide (H₂O₂) accumulation, and enhancing the percentage of antioxidant activities via DPPH test. Moreover, expression levels of several aquaporins were significantly higher in phyA and phyB1B2, and the relative water content (RWC) in leaves was higher than the RWC in the WT under drought stress, suggesting the enhancement of hydration status in the phy mutants. Therefore, inhibition of oxidative damage in phyA and phyB1B2 mutants may mitigate the harmful effects of drought by preventing membrane damage and conserving the plant hydrostatus.

Field evaluation of TaDREB2B-ectopic expression sugarcane (Saccharum spp. hybrid) for drought tolerance

Sugarcane is one of the most crucial sugar crops globally that supplies the main raw material for sugar and ethanol production, but drought stress causes a severe decline in sugarcane yield worldwide. Enhancing sugarcane drought resistance and reducing yield and quality losses is an ongoing challenge in sugarcane genetic improvement. Here, we introduced a Tripidium arundinaceum dehydration-responsive element-binding transcription factor (TaDREB2B) behind the drought-responsible RD29A promoter into a commercial sugarcane cultivar FN95-1702 and subsequently conducted a series of drought tolerance experiments and investigation of agronomic and quality traits. Physiological analysis indicated that Prd29A: TaDREB2B transgenic sugarcane significantly confers drought tolerance in both the greenhouses and the field by enhancing water retention capacity and reducing membrane damage without compromising growth. These transgenic plants exhibit obvious improvements in yield performance and various physiological traits under the limited-irrigation condition in the field, such as increasing 41.9% yield and 44.4% the number of ratooning sugarcane seedlings. Moreover, Prd29A: TaDREB2B transgenic plants do not penalize major quality traits, including sucrose content, gravity purity, Brix, etc. Collectively, our results demonstrated that the Prd29A-TaDREB2B promoter-transgene combination will be a useful biotechnological tool for the increase of drought tolerance and the minimum of yield losses in sugarcane.

QTL mapping of drought-related traits in the hybrids of Populus deltoides 'Danhong'×Populus simonii 'Tongliao1'

BACKGROUND

Poplar trees provide a large amount of wood material, but many parts of the world are arid or semi-arid areas because of insufficient annual precipitation, which seriously affects the growth of poplar trees. Populus simonii 'Tongliao1' shows strong tolerance to stress environments, and Populus deltoides 'Danhong' shows a stronger growth rate in a suitable environment. To identify drought tolerance-related QTLs and genes, an F₁ population derived from the cross between the 'Danhong' and 'Tongliao 1' Populus was assessed under drought stress.

RESULTS

We measured drought-related traits such as the relative height growth, relative diameter growth, leaf senescence number, specific leaf area, and leaf relative water content in the population under control and drought environments. The results showed that drought stress reduced the plant height relative growth, ground diameter relative growth, specific leaf area and leaf relative water content and increased the number of leaf drops. A total of 208 QTLs were identified by QTL mapping analysis, and they consisted of 92, 63 and 53 QTLs under control, drought stress treatment and drought index conditions, respectively. A molecular identification marker for drought tolerance, np2841, which was associated with a QTL (qDLRWC-LG10-1) for relative leaf water content, was initially developed. We mined 187 candidate genes for QTL regions of five traits under a drought environment. The reference genome annotation for Populus trichocarpa and a homologous gene analysis of Arabidopsis thaliana identified two candidate genes, Potri.003G171300 and Potri.012G123900, with significant functions in response to drought stress. We identified five key regulatory genes (Potri.006G273500, Potri.007G111500, Potri.007G111600, Potri.007G111700, and Potri.007G111800) related to drought tolerance through the poplar coexpression network.

CONCLUSION

In this study, our results indicate that the QTLs can effectively enhance the drought tolerance of poplar. It is a step closer towards unravelling the genetic basis of poplar drought tolerance-related traits, and to providing validated candidate genes and molecular markers for future genetic improvement.

Metabolic Pathways Involved in the Drought Stress Response of Nitraria tangutorum as Revealed by Transcriptome Analysis

Drought resistance in plants is controlled by multiple genes. To identify the genes that mediate drought stress responses and to assess the associated metabolic pathways in the desert shrub Nitraria tangutorum, we conducted a transcriptome analysis of plants under control (maximum field capacity) and drought (20% of the maximum field capacity) conditions. We analyzed differentially expressed genes (DEGs) of N. tangutorum and their enrichment in the KEGG metabolic pathways database, and explored the molecular biological mechanisms underlying the answer to its drought tolerance. Between the control and drought groups, 119 classified metabolic pathways annotated 3047 DEGs in the KEGG database. For drought tolerance, nitrate reductase (NR) gene expression was downregulated, indicating that NR activity was decreased to improve drought tolerance. In ammonium assimilation, drought stress inhibited glutamine formation. Protochlorophyllide reductase (1.3.1.33) expression was upregulated to promote chlorophyll a synthesis, whereas divinyl reductase (1.3.1.75) expression was downregulated to inhibit chlorophyll-ester a synthesis. The expression of the chlorophyll synthase (2.5.1.62) gene was downregulated, which affected the synthesis of chlorophyll a and b. Overall, drought stress appeared to improve the ability to convert chlorophyll b into chlorophyll a. Our data serve as a theoretical foundation for further elucidating the growth regulatory mechanism of desert xerophytes, thereby facilitating the development and cultivation of new, drought-resistant genotypes for the purpose of improving desert ecosystems.