Methods and concepts in quantifying resistance to drought, salt and freezing, abiotic stresses that affect plant water status

The multidimensionality of plant drought stress: The relative importance of edaphic and atmospheric drought

Drought threatens plant growth and related ecosystem services. The emergence of plant drought stress under edaphic drought is well studied, whilst the importance of atmospheric drought only recently gained momentum. Yet, little is known about the interaction and relative contribution of edaphic and atmospheric drought on the emergence of plant drought stress. We conducted a gradient experiment, fully crossing gravimetric water content (GWC: maximum water holding capacity-permanent wilting point) and vapour pressure deficit (VPD: 1-2.25 kPa) using five wheat varieties from three species (Triticum monococcum, T. durum & T. aestivum). We quantified the occurrence of plant drought stress on molecular (abscisic acid), cellular (stomatal conductance), organ (leaf water potential) and stand level (evapotranspiration). Plant drought stress increased with decreasing GWC across all organizational levels. This effect was magnified nonlinearly by VPD after passing a critical threshold of soil water availability. At around 20%GWC (soil matric potential 0.012 MPa), plants lost their ability to regulate leaf water potential via stomata regulation, followed by the emergence of hydraulic dysfunction. The emergence of plant drought stress is characterized by changing relative contributions of soil versus atmosphere and their non-linear interaction. This highly non-linear response is likely to abruptly alter plant-related ecosystem services in a drying world.

The nonphototrophic hypocotyl 3 (NPH3) domain protein NRL5 is a trafficking-associated GTPase essential for drought resistance

The mechanisms of plant drought resistance are unclear but may involve membrane trafficking and metabolic reprogramming, including proline accumulation. Forward genetic screening using a proline dehydrogenase 1 (ProDH1) promoter:reporter identified a drought hypersensitive mutant with a single-amino acid substitution (P335L) in the nonphototrophic hypocotyl 3 (NPH3) domain of NPH3/root phototropism 2-like 5 (NRL5)/naked pins in Yucca 8 (NPY8). Further experiments found that NRL5 and other NPH3 domain proteins are guanosine triphosphatases (GTPases). NRL5, but not NRL5P335L, interacted with the RABE1c and RABH1b GTPases and the soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) Vesicle-Associated Membrane Protein (VAMP)721/722. These proteins controlled NRL5 localization and connection to trafficking while also being genetically downstream of, and potentially regulated by, NRL5. These data demonstrate that NRL5-mediated restraint of proline catabolism is required for drought resistance and also reveal unexpected functions of the NPH3 domain such that the role of NPH3 domain proteins in signaling, trafficking, and cellular polarity can be critically reevaluated.

Integrative analysis of transcriptome and metabolome reveal the differential tolerance mechanisms to low and high salinity in the roots of facultative halophyte Avicennia marina

Mangroves perform a crucial ecological role along the tropical and subtropical coastal intertidal zone where salinity fluctuation occurs frequently. However, the differential responses of mangrove plant at the combined transcriptome and metabolome level to variable salinity are not well documented. In this study, we used Avicennia marina (Forssk.) Vierh., a pioneer species of mangrove wetlands and one of the most salt-tolerant mangroves, to investigate the differential salt tolerance mechanisms under low and high salinity using inductively coupled plasma-mass spectrometry, transcriptomic and metabolomic analysis. The results showed that HAK8 was up-regulated and transported K+ into the roots under low salinity. However, under high salinity, AKT1 and NHX2 were strongly induced, which indicated the transport of K+ and Na+ compartmentalization to maintain ion homeostasis. In addition, A. marina tolerates low salinity by up-regulating ABA signaling pathway and accumulating more mannitol, unsaturated fatty acids, amino acids' and L-ascorbic acid in the roots. Under high salinity, A. marina undergoes a more drastic metabolic network rearrangement in the roots, such as more L-ascorbic acid and oxiglutatione were up-regulated, while carbohydrates, lipids and amino acids were down-regulated in the roots, and, finally, glycolysis and TCA cycle were promoted to provide more energy to improve salt tolerance. Our findings suggest that the major salt tolerance traits in A. marina can be attributed to complex regulatory and signaling mechanisms, and show significant differences between low and high salinity.

Cytokinin oxidase2-deficient mutants improve panicle and grain architecture through cytokinin accumulation and enhance drought tolerance in indica rice

KEY MESSAGE

The Osckx2 mutant accumulates cytokinin thereby enhancing panicle branching, grain yield, and drought tolerance, marked by improved survival rate, membrane integrity, and photosynthetic function. Cytokinins (CKs) are multifaceted hormones that regulate growth, development, and stress responses in plants. Cytokinins have been implicated in improved panicle architecture and grain yield; however, they are inactivated by the enzyme cytokinin oxidase (CKX). In this study, we developed a cytokinin oxidase 2 (Osckx2)-deficient mutant using CRISPR/Cas9 gene editing in indica rice and assessed its function under water-deficit and salinity conditions. Loss of OsCKX2 function increased grain number, secondary panicle branching, and overall grain yield through improved cytokinin content in the panicle tissue. Under drought conditions, the Osckx2 mutant conserved more water and demonstrated improved water-saving traits. Through reduced transpiration, Osckx2 mutants showed an improved survival response than the wild type to unset dehydration stress. Further, Osckx2 maintained chloroplast and membrane integrity and showed significantly improved photosynthetic function under drought conditions through enhanced antioxidant protection systems. The OsCKX2 function negatively affects panicle grain number and drought tolerance, with no discernible impact in response to salinity. The finding suggests the utility of the beneficial Osckx2 allele in breeding to develop climate-resilient, high-yielding cultivars for future food security.

Combined transcriptomics and metabolomics analysis reveals salinity stress specific signaling and tolerance responses in the seagrass Zostera japonica

KEY MESSAGE

Multiple regulatory pathways of Zostera japonica to salt stress were identified through growth, physiological, transcriptomic and metabolomic analyses. Seagrasses are marine higher submerged plants that evolved from terrestrial monocotyledons and have fully adapted to the high saline seawater environment during the long evolutionary process. As one of the seagrasses growing in the intertidal zone, Zostera japonica not only has the ability to quickly adapt to short-term salt stress but can also survive at salinities ranging from the lower salinity of the Yellow River estuary to the higher salinity of the bay, making it a good natural model for studying the mechanism underlying the adaptation of plants to salt stress. In this work, we screened the growth, physiological, metabolomic, and transcriptomic changes of Z. japonica after a 5-day exposure to different salinities. We found that high salinity treatment impeded the growth of Z. japonica, hindered its photosynthesis, and elicited oxidative damage, while Z. japonica increased antioxidant enzyme activity. At the transcriptomic level, hypersaline stress greatly reduced the expression levels of photosynthesis-related genes while increasing the expression of genes associated with flavonoid biosynthesis. Meanwhile, the expression of candidate genes involved in ion transport and cell wall remodeling was dramatically changed under hypersaline stress. Moreover, transcription factors signaling pathways such as mitogen-activated protein kinase (MAPK) were also significantly influenced by salt stress. At the metabolomic level, Z. japonica displayed an accumulation of osmolytes and TCA mediators under hypersaline stress. In conclusion, our results revealed a complex regulatory mechanism in Z. japonica under salt stress, and the findings will provide important guidance for improving salt resistance in crops.

Trait variation and performance across varying levels of drought stress in cultivated sunflower (Helianthus annuus L.)

Drought is a major agricultural challenge that is expected to worsen with climate change. A better understanding of drought responses has the potential to inform efforts to breed more tolerant plants. We assessed leaf trait variation and covariation in cultivated sunflower (Helianthus annuus L.) in response to water limitation. Plants were grown under four levels of water availability and assessed for environmentally induced plasticity in leaf stomatal and vein traits as well as biomass (performance indicator), mass fractions, leaf area, leaf mass per area, and chlorophyll content. Overall, biomass declined in response to stress; these changes were accompanied by responses in leaf-level traits including decreased leaf area and stomatal size, and increased stomatal and vein density. The magnitude of trait responses increased with stress severity and relative plasticity of smaller-scale leaf anatomical traits was less than that of larger-scale traits related to construction and growth. Across treatments, where phenotypic plasticity was observed, stomatal density was negatively correlated with stomatal size and positively correlated with minor vein density, but the correlations did not hold up within treatments. Four leaf traits previously shown to reflect major axes of variation in a large sunflower diversity panel under well-watered conditions (i.e. stomatal density, stomatal pore length, vein density, and leaf mass per area) predicted a surprisingly large amount of the variation in biomass across treatments, but trait associations with biomass differed within treatments. Additionally, the importance of these traits in predicting variation in biomass is mediated, at least in part, through leaf size. Our results demonstrate the importance of leaf anatomical traits in mediating drought responses in sunflower, and highlight the role that phenotypic plasticity and multi-trait phenotypes can play in predicting productivity under complex abiotic stresses like drought.

Salt tolerance in a neotropical orchid in the absence of local adaptation to salt spray

PREMISE

Salt tolerance has rarely been investigated regionally in the neotropics and even more rarely in Orchidaceae, one of the largest families. Therefore, investigating local adaptation to salt spray and its physiological basis in Epidendrum fulgens, a neotropical orchid species, brings important new insights.

METHODS

We assessed the degree of salt tolerance in E. fulgens by testing whether coastal populations are more tolerant to salt, which could point to local adaptation. To understand the physiological basis of such salt tolerance, we exposed wild-collected individuals to salt spray for 60 days, then measured leaf expansion, osmotic potential, sodium leaf concentration, chlorophyll leaf index, chlorophyll fluorescence, relative growth rate, and pressure-volume curves.

RESULTS

There is no local adaptation to salt spray since both inland and coastal plants have a high tolerance to salt stress. This tolerance is explained by the ability to tolerate high concentrations of salt in leaf tissues, which is related to the high succulence displayed by this species.

CONCLUSIONS

We showed an unprecedented salt tolerance level for an orchid species, highlighting our limited knowledge of that trait beyond the traditional studied groups. Another interesting finding is that salt tolerance in E. fulgens is linked to succulence, is widespread, and is not the result of local adaptation. We suggest that E. fulgens and its allied species could be an interesting group to explore the evolution of important traits related to tolerance to salt stress, like succulence.

Arabidopsis transcriptome responses to low water potential using high-throughput plate assays

Soil-free assays that induce water stress are routinely used to investigate drought responses in the plant Arabidopsis thaliana. Due to their ease of use, the research community often relies on polyethylene glycol (PEG), mannitol, and salt (NaCl) treatments to reduce the water potential of agar media, and thus induce drought conditions in the laboratory. However, while these types of stress can create phenotypes that resemble those of water deficit experienced by soil-grown plants, it remains unclear how these treatments compare at the transcriptional level. Here, we demonstrate that these different methods of lowering water potential elicit both shared and distinct transcriptional responses in Arabidopsis shoot and root tissue. When we compared these transcriptional responses to those found in Arabidopsis roots subject to vermiculite drying, we discovered many genes induced by vermiculite drying were repressed by low water potential treatments on agar plates (and vice versa). Additionally, we also tested another method for lowering water potential of agar media. By increasing the nutrient content and tensile strength of agar, we show the 'hard agar' (HA) treatment can be leveraged as a high-throughput assay to investigate natural variation in Arabidopsis growth responses to low water potential.

Genome-Wide Identification of the TGA Gene Family and Expression Analysis under Drought Stress in Brassica napus L

TGA transcription factors belong to Group D of the bZIP transcription factors family and play vital roles in the stress response of plants. Brassica napus is an oil crop with rich economic value. However, a systematic analysis of TGA gene family members in B. napus has not yet been reported. In this study, we identified 39 full-length TGA genes in B. napus, renamed TGA1~TGA39. Thirty-nine BnTGA genes were distributed on 18 chromosomes, mainly located in the nucleus, and differences were observed in their 3D structures. Phylogenetic analysis showed that 39 BnTGA genes could be divided into five groups. The BnTGA genes in the same group had similar structure and motif compositions, and all the BnTGA genes had the same conserved bZIP and DOG1 domains. Phylogenetic and synteny analysis showed that the BnTGA genes had a close genetic relationship with the TGA genes of the Brassica juncea, and BnTGA11 and BnTGA29 may play an important role in evolution. In addition, qRT-PCR revealed that three genes (BnTGA14/17/23) showed significant changes in eight experimental materials after drought treatment. Meanwhile, it can be inferred from the results of drought treatment on different varieties of rapeseed that the stress tolerance of parental rapeseed can be transmitted to the offspring through hybridization. In short, these findings have promoted the understanding of the B. napus TGA gene family and will contribute to future research aimed at B. napus resistant breeding.

Arabidopsis SNARE SYP132 impacts on PIP2;1 trafficking and function in salinity stress

In plants so-called plasma membrane intrinsic proteins (PIPs) are major water channels governing plant water status. Membrane trafficking contributes to functional regulation of major PIPs and is crucial for abiotic stress resilience. Arabidopsis PIP2;1 is rapidly internalised from the plasma membrane in response to high salinity to regulate osmotic water transport, but knowledge of the underlying mechanisms is fragmentary. Here we show that PIP2;1 occurs in complex with SYNTAXIN OF PLANTS 132 (SYP132) together with the plasma membrane H+-ATPase AHA1 as evidenced through in vivo and in vitro analysis. SYP132 is a multifaceted vesicle trafficking protein, known to interact with AHA1 and promote endocytosis to impact growth and pathogen defence. Tracking native proteins in immunoblot analysis, we found that salinity stress enhances SYP132 interactions with PIP2;1 and PIP2;2 isoforms to promote redistribution of the water channels away from the plasma membrane. Concurrently, AHA1 binding within the SYP132-complex was significantly reduced under salinity stress and increased the density of AHA1 proteins at the plasma membrane in leaf tissue. Manipulating SYP132 function in Arabidopsis thaliana enhanced resilience to salinity stress and analysis in heterologous systems suggested that the SNARE influences PIP2;1 osmotic water permeability. We propose therefore that SYP132 coordinates AHA1 and PIP2;1 abundance at the plasma membrane and influences leaf hydraulics to regulate plant responses to abiotic stress signals.

Functional in vitro diversity of an intrinsically disordered plant protein during freeze-thawing is encoded by its structural plasticity

Intrinsically disordered late embryogenesis abundant (LEA) proteins play a central role in the tolerance of plants and other organisms to dehydration brought upon, for example, by freezing temperatures, high salt concentration, drought or desiccation, and many LEA proteins have been found to stabilize dehydration-sensitive cellular structures. Their conformational ensembles are highly sensitive to the environment, allowing them to undergo conformational changes and adopt ordered secondary and quaternary structures and to participate in formation of membraneless organelles. In an interdisciplinary approach, we discovered how the functional diversity of the Arabidopsis thaliana LEA protein COR15A found in vitro is encoded in its structural repertoire, with the stabilization of membranes being achieved at the level of secondary structure and the stabilization of enzymes accomplished by the formation of oligomeric complexes. We provide molecular details on intra- and inter-monomeric helix-helix interactions, demonstrate how oligomerization is driven by an α-helical molecular recognition feature (α-MoRF) and provide a rationale that the formation of noncanonical, loosely packed, right-handed coiled-coils might be a recurring theme for homo- and hetero-oligomerization of LEA proteins.

ARGONAUTE10 controls cell fate specification and formative cell divisions in the Arabidopsis root

A key question in plant biology is how oriented cell divisions are integrated with patterning mechanisms to generate organs with adequate cell type allocation. In the root vasculature, a gradient of miRNA165/6 controls the abundance of HD-ZIP III transcription factors, which in turn control cell fate and spatially restrict vascular cell proliferation to specific cells. Here, we show that vascular development requires the presence of ARGONAUTE10, which is thought to sequester miRNA165/6 and protect HD-ZIP III transcripts from degradation. Our results suggest that the miR165/6-AGO10-HDZIP III module acts by buffering cytokinin responses and restricting xylem differentiation. Mutants of AGO10 show faster growth rates and strongly enhanced survival under severe drought conditions. However, this superior performance is offset by markedly increased variation and phenotypic plasticity in sub-optimal carbon supply conditions. Thus, AGO10 is required for the control of formative cell division and coordination of robust cell fate specification of the vasculature, while altering its expression provides a means to adjust phenotypic plasticity.

Current views of drought research: experimental methods, adaptation mechanisms and regulatory strategies

Drought stress is one of the most important abiotic stresses which causes many yield losses every year. This paper presents a comprehensive review of recent advances in international drought research. First, the main types of drought stress and the commonly used drought stress methods in the current experiment were introduced, and the advantages and disadvantages of each method were evaluated. Second, the response of plants to drought stress was reviewed from the aspects of morphology, physiology, biochemistry and molecular progression. Then, the potential methods to improve drought resistance and recent emerging technologies were introduced. Finally, the current research dilemma and future development direction were summarized. In summary, this review provides insights into drought stress research from different perspectives and provides a theoretical reference for scholars engaged in and about to engage in drought research.

Genome-wide characterization and expression analysis of GATA transcription factors under combination of light wavelengths and drought stress in potato

GATA is one of the prominent transcription factor families conserved among many organisms in eukaryotes and has different biological roles in many pathways, particularly in light regulation in plants. Although GATA transcription factors (TFs) have been identified in different crop species, their roles in abiotic stress tolerance have not been studied in potato. In this study, we identified 32 GATA TFs in potato (Solanum tuberosum) by in silico analyses, and expression levels of selected six genes were investigated in drought-tolerant (Sante) and sensitive (Agria) cultivars under light, drought, and combined (light + drought) stress conditions. According to the phylogenetic results, StGATA TFs were divided into four main groups (I, II, III, and IV) and different sub-groups in I and II (eight and five, respectively). StGATA genes were uniformly localized to each chromosome with a conserved exon/intron structure. The presence of cis-elements within the StGATA family further supported the possible involvement in abiotic stress tolerance and light response, tissue-specific expression, and hormonal regulation. Additional PPI investigations showed that these networks, especially for Groups I, II, and IV, play a significant role in response to light and drought stress. Six StGATAs were chosen from these groups for expressional profiling, and their expression in both Sante and Agria was mainly downregulated under purple and red lights, drought, and combined stress (blue + drought and purple + drought). The interactomes of selected StGATAs, StGATA3, StGATA24, and StGATA29 were analyzed, and the accessions with GATA motifs were checked for expression. The results showed that the target proteins, cyclin-P3-1, SPX domain-containing protein 1, mitochondrial calcium uniporter protein 2, mitogen-activated protein kinase kinase kinase YODA, and splicing factor 3 B subunit 4-like, mainly play a role in phytochrome-mediated stomatal patterning, development, and activity. Understanding the interactions between drought stress and the light response mechanisms in potato plants is essential. It will eventually be possible to enhance potato resilience to climate change by manipulating the TFs that play a role in these pathways.

Cultivated sunflower (Helianthus annuus L.) has lower tolerance of moderate drought stress than its con-specific wild relative, but the underlying traits remain elusive

Cultivated crops are generally expected to have less abiotic stress tolerance than their wild relatives. However, this assumption is not well supported by empirical literature and may depend on the type of stress and how it is imposed, as well as the measure of tolerance being used. Here, we investigated whether wild and cultivated accessions of Helianthus annuus differed in stress tolerance assessed as proportional decline in biomass due to drought and whether wild and cultivated accessions differed in trait responses to drought and trait associations with tolerance. In a greenhouse study, H. annuus accessions in the two domestication classes (eight cultivated and eight wild accessions) received two treatments: a well-watered control and a moderate drought implemented as a dry down followed by maintenance at a predetermined soil moisture level with automated irrigation. Treatments were imposed at the seedling stage, and plants were harvested after 2 weeks of treatment. The proportional biomass decline in response to drought was 24% for cultivated H. annuus accessions but was not significant for the wild accessions. Thus, using the metric of proportional biomass decline, the cultivated accessions had less drought tolerance. Among accessions, there was no tradeoff between drought tolerance and vigor assessed as biomass in the control treatment. In a multivariate analysis, wild and cultivated accessions did not differ from each other or in response to drought for a subset of morphological, physiological, and allocational traits. Analyzed individually, traits varied in response to drought in wild and/or cultivated accessions, including declines in specific leaf area, leaf theoretical maximum stomatal conductance (gsmax), and stomatal pore length, but there was no treatment response for stomatal density, succulence, or the ability to osmotically adjust. Focusing on traits associations with tolerance, plasticity in gsmax was the most interesting because its association with tolerance differed by domestication class (although the effects were relatively weak) and thus might contribute to lower tolerance of cultivated sunflower. Our H. annuus results support the expectation that stress tolerance is lower in crops than wild relatives under some conditions. However, determining the key traits that underpin differences in moderate drought tolerance between wild and cultivated H. annuus remains elusive.

Adaptation mechanisms of leaf vein traits to drought in grassland plants

Leaf veins play an important role in water transport, and are closely associated with photosynthesis and transpiration. Resource heterogeneity in the environment, particularly in water resources, causes changes in leaf vein structure and function, thereby affecting plant growth and community assemblages. Therefore, it is necessary to explore the spatial variation and evolutionary mechanisms of leaf veins in natural communities. Natural communities are composed of dominant and non-dominant species. However, few studies to date have explored the trait variation of dominant and non-dominant species on a large scale. In this study, we set up 10 sampling sites along the water gradient (from east to west) in the Loess Plateau of China, and measured and calculated the vein density (vein length per unit area, VLA), vein diameter (VD), and vein volume ratio (VVR) of 173 species, including dominant and non-dominant species. The mean values of VLA, VD, and VVR were 10.95 mm mm-2, 22.24 μm, and 3%, respectively. VD and VVR of the dominant species were significantly higher than those of the non-dominant species. Unexpectedly, there was no significant change in the VLA with the water gradient, although the VD increased with drought. Leaf vein traits did not change significantly with evolution. There was a significant trade-off between VLA and VD. Our findings demonstrate that the response of veins to environmental changes is dependent on the degree of drought and provide new insights for further large-scale studies.

A Roadmap from Functional Materials to Plant Health Monitoring (PHM)

Soft bioelectronics have great potential for the early diagnosis of plant diseases and the mitigation of adverse outcomes such as reduced crop yields and stunted growth. Over the past decade, bioelectronic interfaces have evolved into miniaturized conformal electronic devices that integrate flexible monitoring systems with advanced electronic functionality. This development is largely attributable to advances in materials science, and micro/nanofabrication technology. The approach uses the mechanical and electronic properties of functional materials (polymer substrates and sensing elements) to create interfaces for plant monitoring. In addition to ensuring biocompatibility, several other factors need to be considered when developing these interfaces. These include the choice of materials, fabrication techniques, precision, electrical performance, and mechanical stability. In this review, some of the benefits plants can derive from several of the materials used to develop soft bioelectronic interfaces are discussed. The article describes how they can be used to create biocompatible monitoring devices that can enhance plant growth and health. Evaluation of these devices also takes into account features that ensure their long-term durability, sensitivity, and reliability. This article concludes with a discussion of the development of reliable soft bioelectronic systems for plants, which has the potential to advance the field of bioelectronics.

Genome-wide association analysis reveals genes controlling an antagonistic effect of biotic and osmotic stress on Arabidopsis thaliana growth

While the response of Arabidopsis thaliana to drought, herbivory or fungal infection has been well-examined, the consequences of exposure to a series of such (a)biotic stresses are not well studied. This work reports on the genetic mechanisms underlying the Arabidopsis response to single osmotic stress, and to combinatorial stress, either fungal infection using Botrytis cinerea or herbivory using Pieris rapae caterpillars followed by an osmotic stress treatment. Several small-effect genetic loci associated with rosette dry weight (DW), rosette water content (WC), and the projected rosette leaf area in response to combinatorial stress were mapped using univariate and multi-environment genome-wide association approaches. A single-nucleotide polymorphism (SNP) associated with DROUGHT-INDUCED 19 (DI19) was identified by both approaches, supporting its potential involvement in the response to combinatorial stress. Several SNPs were found to be in linkage disequilibrium with known stress-responsive genes such as PEROXIDASE 34 (PRX34), BASIC LEUCINE ZIPPER 25 (bZIP25), RESISTANCE METHYLATED GENE 1 (RMG1) and WHITE RUST RESISTANCE 4 (WRR4). An antagonistic effect between biotic and osmotic stress was found for prx34 and arf4 mutants, which suggests PRX34 and ARF4 play an important role in the response to the combinatorial stress.

Characterization and transformation of TtMYB1 transcription factor from Tritipyrum to improve salt tolerance in wheat

BACKGROUND

Common wheat (Triticum aestivum L.) is a worldwide cereal crop, which is an integral part of the diets of many countries. In addition, the MYB gene of wheat plays a role in the response to salt stress.

RESULTS

"Y1805" is a Tritipyrum variety that is relatively tolerant to salt. We used transcriptome analysis to show that the "Y1805" MYB gene was both highly expressed and sensitive to salt stress. Compared with control roots, the level of MYB expression during salt stress was higher, which rapidly decreased to control levels during the recovery process. MYB gene relative expression showed the highest levels in "Y1805" roots during salt stress, with the stems and then leaves being the next highest stressed tissues. The novel MYB gene (TtMYB1) was successfully cloned from "Y1805". It showed a coding sequence length of 783 bp with 95.79% homology with Tel2E01G633100 from Thinopyrum elongatum. TtMYB1 and MYB from Th. elongatum were clustered in the same branch using phylogenetic analysis, which indicated high similarities. The TtMYB1 gene is located in the nucleus. The coleoptile method was employed when a TtMYB1 overexpression vector was used during transformation into "1718" (common wheat). Under high salt stress, TtMYB1 leaves of overexpression lines had decreased wilting, when compared with wild-type (WT) plants. During normal conditions, salt stress, and recovery, the lengths of the roots and the heights of seedlings from the overexpression lines were found to be significantly greater than roots and seedlings of WT plants. In addition, during high salt stress, the overexpression lines showed that proline and soluble sugar levels were higher than that of WT plants, but with lower malondialdehyde levels. Forty-three proteins that interacted with TtMYB1 were identified using the yeast two-hybrid assay. Protein-protein interaction analyses indicated that most were SANT domain-containing and Wd repeat region domain-containing proteins. Among these proteins, ribosomal proteins were the main node. Abiotic stress-related terms (such as "carbonate dehydratase activity", "protein targeting peroxisomes", and "glutathione peroxidase activity") were enriched in GO analysis. In KEGG analysis, "carbohydrate metabolism", "environmental information processing", "genetic information processing", "signaling and cell precursors", and "energy metabolism" pathways were enriched.

CONCLUSION

The TtMYB1 gene might enhance salt tolerance by increasing proline and soluble sugar content and antioxidase activity in transgenic wheat. It therefore has the potential to enhance high salt tolerance in plants.

Cytokinin deficiency confers enhanced tolerance to mild, but decreased tolerance to severe salinity stress in in vitro grown potato

Cytokinin (CK) is a plant hormone that plays crucial roles in regulating plant growth and development. CK-deficient plants are widely used as model systems for investigating the numerous physiological roles of CK. Since it was previously shown that transgenic or mutant CK-deficient Arabidopsis and Centaurium plants show superior tolerance to salinity, we examined the tolerance of three CK-deficient potato lines overexpressing the Arabidopsis thaliana CYTOKININ OXIDASE/DEHYDROGENASE2 (AtCKX2) gene to 50 mM, 100 mM, 150 mM, and 200 mM NaCl applied in vitro. Quantification of visible salinity injury, rooting and acclimatization efficiency, shoot growth, water saturation deficit, and chlorophyll content confirmed that the CK-deficient potato plants were more tolerant to low (50 mM) and moderate (100 mM) NaCl concentrations, but exhibited increased sensitivity to severe salinity stress (150 and 200 mM NaCl) compared to non-transformed control plants. These findings were corroborated by the data distribution patterns according to principal component analysis. Quantification of the activity of superoxide dismutases, peroxidases, and catalases revealed an impaired ability of AtCKX2-transgenic lines to upregulate the activity of antioxidant enzymes in response to salinity, which might contribute to the enhanced sensitivity of these potato lines to severe salt stress. Our results add complexity to the existing knowledge on the regulation of salinity tolerance by CK, as we show for the first time that CK-deficient plants can exhibit reduced rather than increased tolerance to severe salt stress.

LncRNA DANA1 promotes drought tolerance and histone deacetylation of drought responsive genes in Arabidopsis

Although many long noncoding RNAs have been discovered in plants, little is known about their biological function and mode of action. Here we show that the drought-induced long intergenic noncoding RNA DANA1 interacts with the L1p/L10e family member protein DANA1-INTERACTING PROTEIN 1 (DIP1) in the cell nucleus of Arabidopsis, and both DANA1 and DIP1 promote plant drought resistance. DANA1 and DIP1 increase histone deacetylase HDA9 binding to the CYP707A1 and CYP707A2 loci. DIP1 further interacts with PWWP3, a member of the PEAT complex that associates with HDA9 and has histone deacetylase activity. Mutation of DANA1 enhances CYP707A1 and CYP707A2 acetylation and expression resulting in impaired drought tolerance, in agreement with dip1 and pwwp3 mutant phenotypes. Our results demonstrate that DANA1 is a positive regulator of drought response and that DANA1 works jointly with the novel chromatin-related factor DIP1 on epigenetic reprogramming of the plant transcriptome during the response to drought.

Overexpression of a Ramie (Boehmaeria nivea L. Gaud) Group I WRKY Gene, BnWRKY49, Increases Drought Resistance in Arabidopsis thaliana

Plants face multiple stresses in their natural habitats. WRKY transcription factors (TFs) play an important regulatory role in plant stress signaling, regulating the expression of multiple stress-related genes to improve plant stress resistance. In this study, we analyzed the expression profiles of 25 BnWRKY genes in three stages of ramie growth (the seedling stage, the rapid-growth stage, and the fiber maturity stage) and response to abiotic stress through qRT-PCR. The results indicated that 25 BnWRKY genes play a role in different growth stages of ramie and were induced by salt and drought stress in the root and leaf. We selected BnWRKY49 as a candidate gene for overexpression in Arabidopsis. BnWRKY49 was localized in the nucleus. Overexpression of BnWRKY49 affected root elongation under drought and salt stress at the Arabidopsis seedling stage and exhibited increased tolerance to drought stress. Further research found that BnWRKY49-overexpressing lines showed decreased stomatal size and increased cuticular wax deposition under drought compared with wild type (WT). Antioxidant enzyme activities of SOD, POD, and CAT were higher in the BnWRKY49-overexpressing lines than the WT. These findings suggested that the BnWRKY49 gene played an important role in drought stress tolerance in Arabidopsis and laid the foundation for further research on the functional analysis of the BnWRKYs in ramie.

Stress Induces Trait Variability across Multiple Spatial Scales in the Arid Annual Plant Anastatica hierochuntica

Variations in plant characteristics in response to habitat heterogeneity can provide valuable insights into the mechanisms governing plant responses to environmental conditions. In this study, we investigated the role of environmental factors associated with arid conditions in shaping the phenotypic responses of an arid annual plant, Anastatica hierochuntica, across several populations found along an aridity gradient and across multiple spatial scales. Utilizing both field surveys and a net house experiment, we assessed the effects of environmental factors on trait variability within and between populations. The results indicated a significant convergence in plant height due to site aridity, reflecting growth potential based on abiotic resources. Convergence was also observed in the plant's electrolyte leakage with aridity and in plant height concerning soil salinity at specific sites. Phenotypic plasticity was pivotal in maintaining trait variability, with plant height plasticity increasing with soil salinity, SLA plasticity decreasing with aridity, and leaf number plasticity rising with aridity. In conclusion, our findings underscore the adaptive significance of phenotypic variability, especially plasticity, in arid conditions. Notably, trait variability and plasticity did not consistently diminish in stressful settings, emphasizing the adaptive value of flexible responses in such environments.

Effects of freezing temperatures on early life stages of native trees of different elevational origin: implications for tree recruitment in seasonally dry mountain forests

In mountain forests, tree regeneration is limited by increasingly frequent frosts with increasing elevation. We investigated the effects of exposure to freezing temperature on early life stages of two native trees of different elevational origin in a seasonally dry mountain forest. We hypothesized that the negative effects of freezing exposure on performance of early life stages increases as freezing temperature decreases, and that frost resistance increases in plants of high elevational origin. We collected seeds of two tree species (Kageneckia lanceolata and Lithraea molleoides) from populations located at different elevations and grew seedlings and saplings in a greenhouse. Dry seeds, imbibed seeds and 1-month-old seedlings were exposed to seven temperature treatments ranging from 4 °C to -20 °C, while 12-month-old saplings were exposed to four temperature treatments from -8 °C to -20 °C. After freezing exposure in a climate chamber, we monitored seed germination and seedling and sapling survival. Germination of K. lanceolata decreased with decreasing temperature only for imbibed seeds from mid- and high elevations, whereas germination of L. molleoides slightly increased with decreasing temperature only for imbibed seeds from high elevations. For both species, seedling survival decreased with decreasing temperature. For K. lanceolata, the negative effects of freezing temperatures were weaker as elevational origin of seeds increased, whereas L. molleoides showed the opposite pattern. For both species, saplings only survived at the mildest applied freezing temperature (-8 °C). We conclude that effects of climatic variation associated with elevation depend on the study species and life stage. The observed patterns could be caused by maternal effects, which are absent at the sapling stage. Moreover, temperatures below -8 °C can limit recruitment since partial mortality of seedlings and saplings occurred at such values.

AT Hook-Like 10 phosphorylation determines ribosomal RNA processing 6-like 1 (RRP6L1) chromatin association and growth suppression during water stress

Phosphorylation of AT Hook-Like 10 (AHL10), one of the AT-hook family of plant-specific DNA binding proteins, is critical for growth suppression during moderate severity drought (low water potential, ψw ) stress. To understand how AHL10 phosphorylation determines drought response, we identified putative AHL10 interacting proteins and further characterized interaction with RRP6L1, a protein involved in epigenetic regulation. RRP6L1 and AHL10 mutants, as well as ahl10-1rrp6l1-2, had similar phenotypes of increased growth maintenance during low ψw . Chromatin precipitation demonstrated that RRP6L1 chromatin association increased during low ψw stress and was dependent upon AHL10 phosphorylation. Transcriptome analyses showed that AHL10 and RRP6L1 have concordant effects on expression of stress- and development-related genes. Together these results indicate that stress signalling can act via AHL10 phosphorylation to control the chromatin association of the key regulatory protein RRP6L1. AHL10 and RRP6L1 interaction in meristem cells is part of a mechanism to downregulate growth during low ψw stress. Interestingly, the loss of AHL13, which is homologous to AHL10 and phosphorylated at a similar C-terminal site, blocked the enhanced growth maintenance of ahl10-1. Thus, AHL10 and AHL13, despite their close homology, are not redundant but rather have distinct roles, likely related to the formation of AHL hetero-complexes.

Drought resistance evaluation of sugar beet germplasms by response of phenotypic indicators

Sugar beet is a main sugar crop worldwide that often faces drought stress. The identification of drought tolerance of sugar beet germplasms is beneficial for breeding, but the research about it has been rarely reported. In this study, the drought tolerance of germplasms 92005-1, 94002-2 and 92021-1-1 was tested under simulated conditions. Seven days and 9% PEG treatment were the optimal conditions for evaluation, under which more phenotypic indicators showed significant difference in drought tolerance coefficient. The objective weighting and membership function method were established for evaluating the drought tolerance of different sugar beet germplasms. Drought stress decreased the biomass of leaves and roots of sugar beet germplasms. The drought-sensitive germplasm responded faster for leaf weight, root weight, plant height and root length. These indicators declined more significantly under long-term and severe stress. Increasing the root-shoot ratio and proline content were universal strategies of sugar beet germplasms to overcome drought stress. The drought-tolerant germplasms held higher peroxidase activity and better ability to scavenge reactive oxygen for preventing the damage.

Comparison of the Morpho-Physiological and Molecular Responses to Salinity and Alkalinity Stresses in Rice

Rice is a major food crop that has a critical role in ensuring food security for the global population. However, major abiotic stresses such as salinity and alkalinity pose a major threat to rice farming worldwide. Compared with salinity stress, there is limited progress in elucidating the molecular mechanisms associated with alkalinity tolerance in rice. Since both stresses coexist in coastal and arid regions, unraveling of the underlying molecular mechanisms will help the breeding of high-yielding stress-tolerant rice varieties for these areas. This study examined the morpho-physiological and molecular response of four rice genotypes to both salinity and alkalinity stresses. Geumgangbyeo was highly tolerant and Mermentau was the least tolerant to both stresses, while Pokkali and Bengal were tolerant to only salinity and alkalinity stress, respectively. A set of salinity and alkalinity stress-responsive genes showed differential expression in the above rice genotypes under both stress conditions. The expression patterns were consistent with the observed morphological responses in these rice genotypes, suggesting the potential role of these genes in regulating tolerance to these abiotic stresses. Overall, this study suggested that divergence in response to alkalinity and salinity stresses among rice genotypes could be due to different molecular mechanisms conferring tolerance to each stress. In addition to providing a basis for further investigations into differentiating the molecular bases underlying tolerance, this study also emphasizes the possibilities of developing climate-resilient rice varieties using donors that are tolerant to both abiotic stresses.

The Euphrates Poplar Responses to Abiotic Stress and Its Unique Traits in Dry Regions of China (Xinjiang and Inner Mongolia): What Should We Know?

At the moment, drought, salinity, and low-temperature stress are ubiquitous environmental issues. In arid regions including Xinjiang and Inner Mongolia and other areas worldwide, the area of tree plantations appears to be rising, triggering tree growth. Water is a vital resource in the agricultural systems of countries impacted by aridity and salinity. Worldwide efforts to reduce quantitative yield losses on Populus euphratica by adapting tree plant production to unfavorable environmental conditions have been made in response to the responsiveness of the increasing control of water stress. Although there has been much advancement in identifying the genes that resist abiotic stresses, little is known about how plants such as P. euphratica deal with numerous abiotic stresses. P. euphratica is a varied riparian plant that can tolerate drought, salinity, low temperatures, and climate change, and has a variety of water stress adaptability abilities. To conduct this review, we gathered all available information throughout the Web of Science, the Chinese National Knowledge Infrastructure, and the National Center for Biotechnology Information on the impact of abiotic stress on the molecular mechanism and evolution of gene families at the transcription level. The data demonstrated that P. euphratica might gradually adapt its stomatal aperture, photosynthesis, antioxidant activities, xylem architecture, and hydraulic conductivity to endure extreme drought and salt stress. Our analyses will give readers an understanding of how to manage a gene family in desert trees and the influence of abiotic stresses on the productivity of tree plants. They will also give readers the knowledge necessary to improve biotechnology-based tree plant stress tolerance for sustaining yield and quality trees in China's arid regions.

Aldehyde perception induces specific molecular responses in Laminaria digitata and affects algal consumption by a specialist grazer

In the marine environment, distance signaling based on water-borne cues occurs during interactions between macroalgae and herbivores. In the brown alga Laminaria digitata from North-Atlantic Brittany, oligoalginates elicitation or grazing was shown to induce chemical and transcriptomic regulations, as well as emission of a wide range of volatile aldehydes, but their biological roles as potential defense or warning signals in response to herbivores remain unknown. In this context, bioassays using the limpet Patella pellucida and L. digitata were carried out for determining the effects of algal transient incubation with 4-hydroxyhexenal (4-HHE), 4-hydroxynonenal (4-HNE) and dodecadienal on algal consumption by grazers. Simultaneously, we have developed metabolomic and transcriptomic approaches to study algal molecular responses after treatments of L. digitata with these chemical compounds. The results indicated that, unlike the treatment of the plantlets with 4-HNE or dodecadienal, treatment with 4-HHE decreases algal consumption by herbivores at 100 ng.ml-1 . Moreover, we showed that algal metabolome was significantly modified according to the type of aldehydes, and more specifically the metabolite pathways linked to fatty acid degradation. RNAseq analysis further showed that 4-HHE at 100 ng.ml-1 can activate the regulation of genes related to oxylipin signaling pathways and specific responses, compared to oligoalginates elicitation. As kelp beds constitute complex ecosystems consisting of habitat and food source for marine herbivores, the algal perception of specific aldehydes leading to targeted molecular regulations could have an important biological role on kelps/grazers interactions.

DEAD-box RNA helicase 6 regulates drought and abscisic acid stress responses in rapeseed (Brassica napus)

DEAD-box RNA helicase is a major subfamily of RNA helicases with vital roles played in plant growth, development, and plant-environment interactions. RNA helicase 6 in rapeseed (Brassica napus) (BnRH6) is a member of DEAD-box RNA helicase. While previous research has demonstrated the role of BnRH6 in salt stress regulation, the involvement of BnRH6 in drought stress adaptation remains unknown. This report described a function of BnRH6 in drought stress response. BnRH6 was sufficiently induced by osmotic stress. Transgenic Brassica napus and Arabidopsis thaliana (Arabidopsis) overexpressing BnRH6 (OE) showed a drought tolerance phenotype, characterized by improved plant growth, increased survival rates, reduced water loss, leaf chlorosis and oxidative stress. Furthermore, BnRH6 was also induced by exogenous abscisic acid (ABA). BnRH6 overexpression plants exhibited ABA hypersensitivity with lagging seed germination, growth stunt and diminished stomatal opening in the presence of ABA, suggesting the involvement of ABA signal. Assessment of several well-identified drought stress responsive genes such as Calcium-dependent Protein Kinase 14 (BnCDPK14), Enhanced Response to ABA1 (BnERA1) and ABA Insensitive 1 (BnABI1) revealed that their expressions were accordingly changed in BnOE plants, possibly with interplays between BnRH6 and those genes. Our data highlighted the functional role of BnRH6, which plays a positive role in active regulation of drought stress response likely through an ABA-dependent manner in rapeseed plants.

Tripogon loliiformis tolerates rapid desiccation after metabolic and transcriptional priming during initial drying

Crop plants and undomesticated resilient species employ different strategies to regulate their energy resources and growth. Most crop species are sensitive to stress and prioritise rapid growth to maximise yield or biomass production. In contrast, resilient plants grow slowly, are small, and allocate their resources for survival in challenging environments. One small group of plants, termed resurrection plants, survive desiccation of their vegetative tissue and regain full metabolic activity upon watering. However, the precise molecular mechanisms underlying this extreme tolerance remain unknown. In this study, we employed a transcriptomics and metabolomics approach, to investigate the mechanisms of desiccation tolerance in Tripogon loliiformis, a modified desiccation-tolerant plant, that survives gradual but not rapid drying. We show that T. loliiformis can survive rapid desiccation if it is gradually dried to 60% relative water content (RWC). Furthermore, the gene expression data showed that T. loliiformis is genetically predisposed for desiccation in the hydrated state, as evidenced by the accumulation of MYB, NAC, bZIP, WRKY transcription factors along with the phytohormones, abscisic acid, salicylic acid, amino acids (e.g., proline) and TCA cycle sugars during initial drying. Through network analysis of co-expressed genes, we observed differential responses to desiccation between T. loliiformis shoots and roots. Dehydrating shoots displayed global transcriptional changes across broad functional categories, although no enrichment was observed during drying. In contrast, dehydrating roots showed distinct network changes with the most significant differences occurring at 40% RWC. The cumulative effects of the early stress responses may indicate the minimum requirements of desiccation tolerance and enable T. loliiformis to survive rapid drying. These findings potentially hold promise for identifying biotechnological solutions aimed at developing drought-tolerant crops without growth and yield penalties.

Hub Genes in Stable QTLs Orchestrate the Accumulation of Cottonseed Oil in Upland Cotton via Catalyzing Key Steps of Lipid-Related Pathways

Upland cotton is the fifth-largest oil crop in the world, with an average supply of nearly 20% of vegetable oil production. Cottonseed oil is also an ideal alternative raw material to be efficiently converted into biodiesel. However, the improvement in kernel oil content (KOC) of cottonseed has not received sufficient attention from researchers for a long time, due to the fact that the main product of cotton planting is fiber. Previous studies have tagged QTLs and identified individual candidate genes that regulate KOC of cottonseed. The regulatory mechanism of oil metabolism and accumulation of cottonseed are still elusive. In the current study, two high-density genetic maps (HDGMs), which were constructed based on a recombinant inbred line (RIL) population consisting of 231 individuals, were used to identify KOC QTLs. A total of forty-three stable QTLs were detected via these two HDGM strategies. Bioinformatic analysis of all the genes harbored in the marker intervals of the stable QTLs revealed that a total of fifty-one genes were involved in the pathways related to lipid biosynthesis. Functional analysis via coexpression network and RNA-seq revealed that the hub genes in the co-expression network that also catalyze the key steps of fatty acid synthesis, lipid metabolism and oil body formation pathways (ACX4, LACS4, KCR1, and SQD1) could jointly orchestrate oil accumulation in cottonseed. This study will strengthen our understanding of oil metabolism and accumulation in cottonseed and contribute to KOC improvement in cottonseed in the future, enhancing the security and stability of worldwide food supply.

Expression of the plastocyanin gene PETE2 in Camelina sativa improves seed yield and salt tolerance

Plastocyanin functions as an electron carrier in the photosynthetic electron transport chain, located at the thylakoid membrane. In several species, endogenous plastocyanin levels are correlated with the photosynthetic electron transport rate. Overexpression of plastocyanin genes in Arabidopsis thaliana increases plant size, but this phenomenon has not been observed in crop species. Here, we investigated the effects of heterologous expression of a gene encoding a plastocyanin isoform from Arabidopsis, AtPETE2, in the oil seed crop Camelina sativa under standard growth conditions and under salt stress. AtPETE2 heterologous expression enhanced photosynthetic activity in Camelina, accelerating plant development and improving seed yield under standard growth conditions. Additionally, CsPETE2 from Camelina was induced by salt stress and AtPETE2 expression lines had larger primary roots and more lateral roots than the wild type. AtPETE2 expression lines also had larger seeds and higher total seed yield under long-term salt stress compared with non-transgenic Camelina. Our results demonstrate that increased plastocyanin levels in Camelina can enhance photosynthesis and productivity, as well as tolerance to osmotic and salt stresses. Heterologous expression of plastocyanin may be a useful strategy to mitigate crop stress in saline soils.

The synergy of halotolerant PGPB and mauran mitigates salt stress in tomato (Solanum lycopersicum) via osmoprotectants accumulation

Salinity stress is one of the major abiotic factors limiting sustainable agriculture. Halotolerant plant growth-promoting bacteria (PGPB) increased salt stress tolerance in plants, but the mechanisms underlying the tolerance are poorly understood. This study investigated the PGP activity of four halotolerant bacteria under salinity stress and the tomato salt-tolerance mechanisms induced by the synergy of these bacteria with the exopolysaccharide (EPS) mauran. All PGPB tested in this study were able to offer a significant improvement of tomato plant biomass under salinity stress; Peribacillus castrilensis N3 being the most efficient one. Tomato plants treated with N3 and the EPS mauran showed greater tolerance to NaCl than the treatment in the absence of EPS and PGPB. The synergy of N3 with mauran confers salt stress tolerance in tomato plants by increasing sodium transporter genes' expression and osmoprotectant content, including soluble sugars, polyols, proline, GABA, phenols and the polyamine putrescine. These osmolytes together with the induction of sodium transporter genes increase the osmotic adjustment capacity to resist water loss and maintain ionic homeostasis. These findings suggest that the synergy of the halotolerant bacterium N3 and the EPS mauran could enhance tomato plant growth by mitigating salt stress and could have great potential as an inductor of salinity tolerance in the agriculture sector.

Mesoporous silica nanoparticle-induced drought tolerance in Arabidopsis thaliana grown under in vitro conditions

Nanoparticles of varying formats and functionalities have been shown to modify and enhance plant growth and development. Nanoparticles may also be used to improve crop production and performance, particularly under adverse environmental conditions such as drought. Nanoparticles composed of silicon dioxide, especially those that are mesoporous (mesoporous silica nanoparticles; MSNs), have been shown to be taken up by plants; yet their potential to improve tolerance to abiotic stress has not been thoroughly examined. In this study, a range of concentrations of MSNs (0-5000mgL-1 ) were used to determine their effects, in vitro , on Arabidopsis plants grown under polyethylene glycol (PEG)-simulated drought conditions. Treatment of seeds with MSNs during PEG-simulated drought resulted in higher seed germination and then greater primary root length. However, at the highest tested concentration of 5000mgL-1 , reduced germination was found when seeds were subjected to drought stress. At the optimal concentration of 1500mgL-1 , plants treated with MSNs under non-stressed conditions showed significant increases in root length, number of lateral roots, leaf area and shoot biomass. These findings suggest that MSNs can be used to stimulate plant growth and drought stress tolerance.

The 14-3-3 protein OsGF14f interacts with OsbZIP23 and enhances its activity to confer osmotic stress tolerance in rice

Drought, which can induce osmotic stress, is the leading environmental constraint on crop productivity. Plants in both agricultural and natural settings have developed various mechanisms to cope with drought stress. The identification of genes associated with drought stress tolerance and understanding the underlying regulatory mechanisms are prerequisites for developing molecular manipulation strategies to address this issue. Here, we reported that the G-BOX FACTOR 14-3-3f (14-3-3 protein OsGF14f) positively modulates osmotic stress tolerance in rice (Oryza sativa). OsGF14f transgenic lines had no obvious change in crucial agronomic traits including yield and plant height. OsGF14f is transcriptionally induced by PEG treatment, and in rice, overexpression or knockout of this gene leads to enhanced or weakened osmotic stress tolerance, respectively. Furthermore, OsGF14f positively regulates abscisic acid (ABA) responses by interacting with the core ABA-responsive transcription factor BASIC LEUCINE ZIPPER 23 (OsbZIP23) to enhance its transcriptional regulation activity toward downstream target genes. Further genetic analysis showed that OsGF14f is required for the full function of OsbZIP23 in rice osmotic response, and OsGF14f-mediated osmotic stress tolerance partially depends on OsbZIP23. Interestingly, OsGF14f is a direct target gene of OsbZIP23. Taken together, our findings reveal a genetic and molecular framework by which the OsGF14f-OsbZIP23 complex modulates rice osmotic response, providing targets for developing drought-tolerant crops.

Comprehensive in silico analysis of the underutilized crop tef (Eragrostis tef (Zucc.) Trotter) genome reveals drought tolerance signatures

BACKGROUND

Tef (Eragrostis tef) is a C4 plant known for its tiny, nutritious, and gluten-free grains. It contains higher levels of protein, vitamins, and essential minerals like calcium (Ca), iron (Fe), copper (Cu), and zinc (Zn) than common cereals. Tef is cultivated in diverse ecological zones under diverse climatic conditions. Studies have shown that tef has great diversity in withstanding environmental challenges such as drought. Drought is a major abiotic stress severely affecting crop productivity and becoming a bottleneck to global food security. Here, we used in silico-based functional genomic analysis to identify drought-responsive genes in tef and validated their expression using quantitative RT-PCR.

RESULTS

We identified about 729 drought-responsive genes so far reported in six crop plants, including rice, wheat, maize, barley, sorghum, pearl millet, and the model plant Arabidopsis, and reported 20 genes having high-level of GO terms related to drought, and significantly enriched in several biological and molecular function categories. These genes were found to play diverse roles, including water and fluid transport, resistance to high salt, cold, and drought stress, abscisic acid (ABA) signaling, de novo DNA methylation, and transcriptional regulation in tef and other crops. Our analysis revealed substantial differences in the conserved domains of some tef genes from well-studied rice orthologs. We further analyzed the expression of sixteen tef orthologs using quantitative RT-PCR in response to PEG-induced osmotic stress.

CONCLUSIONS

The findings showed differential regulation of some drought-responsive genes in shoots, roots, or both tissues. Hence, the genes identified in this study may be promising candidates for trait improvement in crops via transgenic or gene-editing technologies.

Halotolerant endophytic bacteria alleviate salinity stress in rice (oryza sativa L.) by modulating ion content, endogenous hormones, the antioxidant system and gene expression

Excessive salinity reduces crop production and negatively impacts agriculture worldwide. We previously isolated endophytic bacterial strains from two halophytic species: Artemisia princeps and Chenopodium ficifolium. We used three bacterial isolates: ART-1 (Lysinibacillus fusiformis), ART-10 (Lysinibacillus sphaericus), and CAL-8 (Brevibacterium pityocampae) to alleviate the impact of salinity stress on rice. The impact of 160 mM NaCl salinity on rice was significantly mitigated following inoculation with these bacterial strains, resulting in increased growth and chlorophyll content. Furthermore, OsNHX1, OsAPX1, OsPIN1 and OsCATA expression was increased, but OsSOS expression was decreased. Inductively coupled plasma mass spectrometry (ICP-MS) revealed reduced K+ and Na+ levels in shoots of bacteria-inoculated plants, whereas that of Mg2+ was increased. Bacterial inoculation reduced the content of total flavonoids in rice leaves. Salinized plants inoculated with bacteria showed reduced levels of endogenous salicylic acid (SA) and abscisic acid (ABA) but increased levels of jasmonic acid (JA). In conclusion, the bacterial isolates ART-1, ART-10, and CAL-8 alleviated the adverse effect of salinity on rice growth, which justifies their use as an eco-friendly agricultural practice.

Enhancement of osmotic stress tolerance in soybean seed germination by bacterial bioactive extracts

Soybean (Glycine max (L.) Merr.) is important to the global food industry; however, its productivity is affected by abiotic stresses such as osmosis, flooding, heat, and cold. Here, we evaluated the bioactive extracts of two biostimulant bacterial strains, Bacillus butanolivorans KJ40 and B. siamensis H30-3, for their ability to convey tolerance to osmotic stress in soybean seeds during germination. Soybean seeds were dip-treated in extracts of KJ40 (KJ40E) or H30-3 (H30-3E) and incubated with either 0% or 20% polyethylene glycol 6000 (PEG), simulating drought-induced osmotic stress. We measured malondialdehyde content as a marker for lipid peroxidation, as well as the activity of antioxidant enzymes, including catalase, glutathione peroxidase, and glutathione reductase, together with changes in sugars content. We also monitored the expression of genes involved in the gibberellic acid (GA)-biosynthesis pathway, and abscisic acid (ABA) signaling. Following osmotic stress in the extract-treated seeds, malondialdehyde content decreased, while antioxidant enzyme activity increased. Similarly, the expression of GA-synthesis genes, including GmGA2ox1 and GmGA3 were upregulated in KJ40E-dipped seeds at 12 or 6 h after treatment, respectively. The ABA signaling genes GmABI4 and GmDREB1 were upregulated in H30-3E- and KJ40E-treated seeds at 0 and 12 h after treatment under osmotic stress; however, GmABI5, GmABI4, and GmDREB1 levels were also elevated in the dip-treated seeds in baseline conditions. The GA/ABA ratio increased only in KJ40E-treated seeds undergoing osmotic stress, while glucose content significantly decreased in H30-3E-treated seeds at 24 h after treatment. Collectively, our findings indicated that dip-treatment of soybean seeds in KJ40E and H30-3E can enhance the seeds' resistance to osmotic stress during germination, and ameliorate cellular damage caused by secondary oxidative stress. This seed treatment can be used agriculturally to promote germination under drought stress and lead to increase crop yield and quality.

WRKY transcription factors and OBERON histone-binding proteins form complexes to balance plant growth and stress tolerance

WRKY transcription factors in plants are known to be able to mediate either transcriptional activation or repression, but the mechanism regulating their transcriptional activity is largely unclear. We found that group IId WRKY transcription factors interact with OBERON (OBE) proteins, forming redundant WRKY-OBE complexes in Arabidopsis thaliana. The coiled-coil domain of WRKY transcription factors binds to OBE proteins and is responsible for target gene selection and transcriptional repression. The PHD finger of OBE proteins binds to both histones and WRKY transcription factors. WRKY-OBE complexes repress the transcription of numerous stress-responsive genes and are required for maintaining normal plant growth. Several WRKY and OBE mutants show reduced plant size and increased drought tolerance, accompanied by increased expression of stress-responsive genes. Moreover, expression levels of most of these WRKY and OBE genes are reduced in response to drought stress, revealing a previously uncharacterized regulatory mechanism of the drought stress response. These results suggest that WRKY-OBE complexes repress transcription of stress-responsive genes, and thereby balance plant growth and stress tolerance.

The miRNA-mRNA Regulatory Modules of Pinus massoniana Lamb. in Response to Drought Stress

Masson pine (Pinus massoniana Lamb.) is a major fast-growing woody tree species and pioneer species for afforestation in barren sites in southern China. However, the regulatory mechanism of gene expression in P. massoniana under drought remains unclear. To uncover candidate microRNAs, their expression profiles, and microRNA-mRNA interactions, small RNA-seq was used to investigate the transcriptome from seedling roots under drought and rewatering in P. massoniana. A total of 421 plant microRNAs were identified. Pairwise differential expression analysis between treatment and control groups unveiled 134, 156, and 96 differential expressed microRNAs at three stages. These constitute 248 unique microRNAs, which were subsequently categorized into six clusters based on their expression profiles. Degradome sequencing revealed that these 248 differentially expressed microRNAs targeted 2069 genes. Gene Ontology enrichment analysis suggested that these target genes were related to translational and posttranslational regulation, cell wall modification, and reactive oxygen species scavenging. miRNAs such as miR482, miR398, miR11571, miR396, miR166, miRN88, and miRN74, along with their target genes annotated as F-box/kelch-repeat protein, 60S ribosomal protein, copper-zinc superoxide dismutase, luminal-binding protein, S-adenosylmethionine synthase, and Early Responsive to Dehydration Stress may play critical roles in drought response. This study provides insights into microRNA responsive to drought and rewatering in Masson pine and advances the understanding of drought tolerance mechanisms in Pinus.

Integration of the metabolome and transcriptome reveals the molecular mechanism of drought tolerance in Plumeria rubra

Plumeria rubra L. cv. Acutifolia is an ornamental tree that displays a good drought-tolerance level. However, the molecular mechanisms of P. rubra adaptation to drought stress remains unclear. Here, drought-simulating pot experiments were conducted to explore drought stress response mechanism of P. rubra. Transcriptome analysis revealed 10,967 differentially expressed genes (DEGs), 6,498 of which were increased and 4,469 decreased. Gene Ontology (GO) analysis revealed that the DEGs were enriched in binding category, in metabolic process category, and in catalytic activities category. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that 9 pathways were significantly enriched, including biosynthesis of secondary metabolites (ko01110), plant hormone signal transduction (ko04075) and so on. In addition, the transcription factor families of AP2/ERFs, bZIP, and C2H2 were significantly upregulated while the families of bHLH, MYB-related, and NAC were significantly downregulated. Moreover, the results of metabolomics analysis indicated that some compounds were accumulated under drought stress, especially flavonoids. Overall, it was speculated that under drought stress, P. rubra first activates the plant hormone signal transduction pathway to regulate hormone contents. Then osmotic regulating substances such as organic acids and amino acids are accumulated to maintain osmotic balance. Finally, flavonoid levels are increased to scavenge reactive oxygen species. These results preliminarily revealed the molecular mechanisms adopted by P. rubra in response to drought stress.

Drought stress induced by polyethylene glycol (PEG) in local maize at the early seedling stage

Drought stress adversely impacts growth, crop production, reproductive organ development, and yield characteristics in maize. As a drought-sensitive crop, maize (Zea mays L.) shows considerable varietal differences. A study was conducted at the Tissue Culture Laboratory, Department of Biology, Faculty of Mathematics and Natural Sciences, University of North Sumatra, Medan, Indonesia in order to identify drought-tolerant maize varieties. During germination and early seedling growth, 16 local accessions were evaluated for drought tolerance. Based on local climate and soil conditions, these specific accessions were chosen. The varieties were tested against five levels of drought stress imposed by Polyethylene glycol 6000 (PEG-6000) at 10, 20, 30, 40, and 50%. An experiment with three replications was conducted using a completely randomized design. In the study, local maize accessions (BI3, SB5, DS2, and MN3) and the hybrid variety (H) showed the capability of tolerating drought stress. Generally, germination time, germination percent and vigor index, root and shoot length, shoot ratio, and fresh and dry weight were decreased by increasing PEG concentrations (up to 50%). According to ANOVA results, shoot water content was not significantly affected by the PEG, nor was the interaction between the PEG and the accessions. The root water content, however, was significantly affected by PEG, and the interaction between PEG and accessions. Although interactions between accessions with low PEG concentrations improved germination characteristics, the root histology of the accessions varied. According to drought tolerance indexes, five maize accessions are drought-tolerant, including H (0.683), SB5 (0.617), DS2 (0.565), MN3 (0.512), and BI3 (0.504). The drought-tolerant varieties are recommended in regions with low rainfall or low water sources since they are less water-intensive and produce higher yields.

Allelic variation in transcription factor PtoWRKY68 contributes to drought tolerance in Populus

Drought stress limits woody species productivity and influences tree distribution. However, dissecting the molecular mechanisms that underpin drought responses in forest trees can be challenging due to trait complexity. Here, using a panel of 300 Chinese white poplar (Populus tomentosa) accessions collected from different geographical climatic regions in China, we performed a genome-wide association study (GWAS) on seven drought-related traits and identified PtoWRKY68 as a candidate gene involved in the response to drought stress. A 12-bp insertion and/or deletion and three nonsynonymous variants in the PtoWRKY68 coding sequence categorized natural populations of P. tomentosa into two haplotype groups, PtoWRKY68hap1 and PtoWRKY68hap2. The allelic variation in these two PtoWRKY68 haplotypes conferred differential transcriptional regulatory activities and binding to the promoters of downstream abscisic acid (ABA) efflux and signaling genes. Overexpression of PtoWRKY68hap1 and PtoWRKY68hap2 in Arabidopsis (Arabidopsis thaliana) ameliorated the drought tolerance of two transgenic lines and increased ABA content by 42.7% and 14.3% compared to wild-type plants, respectively. Notably, PtoWRKY68hap1 (associated with drought tolerance) is ubiquitous in accessions in water-deficient environments, whereas the drought-sensitive allele PtoWRKY68hap2 is widely distributed in well-watered regions, consistent with the trends in local precipitation, suggesting that these alleles correspond to geographical adaptation in Populus. Moreover, quantitative trait loci analysis and an electrophoretic mobility shift assay showed that SHORT VEGETATIVE PHASE (PtoSVP.3) positively regulates the expression of PtoWRKY68 under drought stress. We propose a drought tolerance regulatory module in which PtoWRKY68 modulates ABA signaling and accumulation, providing insight into the genetic basis of drought tolerance in trees. Our findings will facilitate molecular breeding to improve the drought tolerance of forest trees.

Phosphate starvation response precedes abscisic acid response under progressive mild drought in plants

Drought severely damages crop production, even under conditions so mild that the leaves show no signs of wilting. However, it is unclear how field-grown plants respond to mild drought. Here, we show through six years of field trials that ridges are a useful experimental tool to mimic mild drought stress in the field. Mild drought reduces inorganic phosphate levels in the leaves to activate the phosphate starvation response (PSR) in soybean plants in the field. Using Arabidopsis thaliana and its mutant plants grown in pots under controlled environments, we demonstrate that PSR occurs before abscisic acid response under progressive mild drought and that PSR plays a crucial role in plant growth under mild drought. Our observations in the field and laboratory using model crop and experimental plants provide insight into the molecular response to mild drought in field-grown plants and the relationship between nutrition and drought stress response.

Brassinosteroids Regulate the Water Deficit and Latex Yield of Rubber Trees

Brassinolide (BR) is an important plant hormone that regulates the growth and development of plants and the formation of yield. The yield and quality of latex from Hevea brasiliensis are regulated by phytohormones. The understanding of gene network regulation mechanism of latex formation in rubber trees is still very limited. In this research, the rubber tree variety CATAS73397 was selected to analyze the relationship between BR, water deficit resistance, and latex yield. The results showed that BR improves the vitality of rubber trees under water deficit by increasing the rate of photosynthesis, reducing the seepage of osmotic regulatory substances, increasing the synthesis of energy substances, and improving the antioxidant system. Furthermore, BR increased the yield and quality of latex by reducing the plugging index and elevating the lutoid bursting index without decreasing mercaptan, sucrose, and inorganic phosphorus. This was confirmed by an increased expression of genes related to latex flow. RNA-seq analysis further indicated that DEG encoded proteins were enriched in the MAPK signaling pathway, plant hormone signal transduction and sucrose metabolism. Phytohormone content displayed significant differences, in that trans-Zeatin, ethylene, salicylic acid, kinetin, and cytokinin were induced by BR, whereas auxin, abscisic acid, and gibberellin were not. In summary, the current research lays a foundation for comprehending the molecular mechanism of latex formation in rubber trees and explores the potential candidate genes involved in natural rubber biosynthesis to provide useful information for further research in relevant areas.

Camellia oleifera CoSWEET10 Is Crucial for Seed Development and Drought Resistance by Mediating Sugar Transport in Transgenic Arabidopsis

Sugar transport from the source leaf to the sink organ is critical for seed development and crop yield, as well as for responding to abiotic stress. SWEETs (sugar will eventually be exported transporters) mediate sugar efflux into the reproductive sink and are therefore considered key candidate proteins for sugar unloading during seed development. However, the specific mechanism underlying the sugar unloading to seeds in Camellia oleifera remains elusive. Here, we identified a SWEET gene named CoSWEET10, which belongs to Clade III and has high expression levels in the seeds of C. oleifera. CoSWEET10 is a plasma membrane-localized protein. The complementation assay of CoSWEET10 in SUSY7/ura3 and EBY.VW4000 yeast strains showed that CoSWEET10 has the ability to transport sucrose, glucose, and fructose. Through the C. oleifera seeds in vitro culture, we found that the expression of CoSWEET10 can be induced by hexose and sucrose, and especially glucose. By generating the restoration lines of CoSWEET10 in Arabidopsis atsweet10, we found that CoSWEET10 restored the seed defect phenotype of the mutant by regulating soluble sugar accumulation and increased plant drought tolerance. Collectively, our study demonstrates that CoSWEET10 plays a dual role in promoting seed development and enhancing plant drought resistance as a sucrose and hexose transporter.

Exogenous Allantoin Confers Rapeseed (Brassica campestris) Tolerance to Simulated Drought by Improving Antioxidant Metabolism and Physiology

Allantoin is an emerging plant metabolite, but its role in conferring drought-induced oxidative stress is still elusive. Therefore, an experiment was devised to explore the role of allantoin (0.5 and 1.0 mM; foliar spray) in rapeseed (Brassica campestris cv. BARI Sarisha-17) under drought. Seedlings at fifteen days of age were subjected to drought, maintaining soil moisture levels at 50% and 25% field capacities, while well-irrigated plants served as the control group. Drought-stressed plants exhibited increased levels of lipid peroxidation and hydrogen peroxide, electrolyte leakage, and impaired glyoxalase systems. Thus, the growth, biomass, and yield attributes of rapeseed were significantly impaired under drought. However, the allantoin-supplemented plants showed a notable increase in their contents of ascorbate and glutathione and decreased dehydroascorbate and glutathione disulfide contents under drought. Moreover, the activity of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase were accelerated with the allantoin spray and the glyoxalase system was also enhanced under drought. Moreover, the improvement in water balance with reduction in proline and potassium ion contents was also observed when allantoin was applied to the plants. Overall, the beneficial effects of allantoin supplementation resulted in the improved plant growth, biomass, and yield of rapeseed under drought conditions. These findings suggest that allantoin acts as an efficient metabolite in mitigating the oxidative stress caused by reactive oxygen species by enhancing antioxidant defense mechanisms and the glyoxalase system.

Calcium-dependent protein kinase GhCDPK4 plays a role in drought and abscisic acid stress responses

Drought is an important factor limiting the yield and quality of cotton. In the present study, the gene encoding the cotton calcium-dependent protein kinase GhCDPK4 was identified and characterized in the transcriptome of cotton under PEG-induced drought stress. In RT-qPCR experiments, GhCDPK4 expression was found to be up-regulated under drought and abscisic acid (ABA) stress. Under drought conditions, heterologous overexpression of GhCDPK4 in tobacco showed a better phenotypic status, higher antioxidant enzyme activity, and lower relative electrolyte leakage (REL) and malondialdehyde (MDA) content. Meanwhile, ghcdpk4-silenced cotton plants, which were extremely sensitive to drought, exhibited higher levels of O^2-，H₂O₂, and MDA contents compared to the control. Meanwhile, silenced lines showed impaired stomatal closure under drought stress, resulting in increased water loss from transpiration in silenced lines. GhCDPK4 expression was induced by ABA, and there are five ABA-responsive elements in its promoter. and C2-DOMAIN ABA-RELATED 4(CAR4, Gh_D09G1653) were found to interact and be co-expressed in the GhCDPK4 interaction network. Therefore, GhCDPK4 may reduce the extent of water loss and oxidative damage in cotton under drought by positively regulating ABA-controlled stomatal closure and reactive oxygen species (ROS) scavenging systems. This study demonstrates the great potential of GhCDPK4 in improving drought resistance in crops.

Overexpression of a rice Tubby-like protein-encoding gene, OsFBT4, confers tolerance to abiotic stresses

The OsFBT4 belongs to a small sub-class of rice F-box proteins called TLPs (Tubby-like proteins) containing the conserved N-terminal F-box domain and a C-terminal Tubby domain. These proteins have largely been implicated in both abiotic and biotic stress responses, besides developmental roles in plants. Here, we investigated the role of OsFBT4 in abiotic stress signalling. The OsFBT4 transcript was strongly upregulated in response to different abiotic stresses in rice, including exogenous ABA. When ectopically expressed, in Arabidopsis, under a constitutive CaMV 35S promoter, the overexpression (OE) caused hypersensitivity to most abiotic stresses, including ABA, during seed germination and early seedling growth. At the 5-day-old seedling growth stage, the OE conferred tolerance to all abiotic stresses. The OE lines displayed significant tolerance to salinity and water deficit at the mature growth stage. The stomatal size and density were seen to be altered in the OE lines, accompanied by hypersensitivity to ABA and hydrogen peroxide (H₂O₂) and a reduced water loss rate. Overexpression of OsFBT4 caused upregulation of several ABA-regulated/independent stress-responsive genes at more advanced stages of growth, showing wide and intricate roles played by OsFBT4 in stress signalling. The OsFBT4 showed interaction with several OSKs (Oryza SKP1 proteins) and localized to the plasma membrane (PM). The protein translocates to the nucleus, in response to oxidative and osmotic stresses, but failed to show transactivation activity in the yeast system. The OE lines also displayed morphological deviations from the wild-type (WT) plants, suggesting a role of the gene also in plant development.