HSP70-16 and VDAC3 jointly inhibit seed germination under cold stress in Arabidopsis

Using a thermal gradient table to study plant temperature signalling and response across a temperature spectrum

Plants must cope with ever-changing temperature conditions in their environment. In many plant species, suboptimal high and low temperatures can induce adaptive mechanisms that allow optimal performance. Thermomorphogenesis is the acclimation to high ambient temperature, whereas cold acclimation refers to the acquisition of cold tolerance following a period of low temperatures. The molecular mechanisms underlying thermomorphogenesis and cold acclimation are increasingly well understood but neither signalling components that have an apparent role in acclimation to both cold and warmth, nor factors determining dose-responsiveness, are currently well defined. This can be explained in part by practical limitations, as applying temperature gradients requires the use of multiple growth conditions simultaneously, usually unavailable in research laboratories. Here we demonstrate that commercially available thermal gradient tables can be used to grow and assess plants over a defined and adjustable steep temperature gradient within one experiment. We describe technical and thermodynamic aspects and provide considerations for plant growth and treatment. We show that plants display the expected morphological, physiological, developmental and molecular responses that are typically associated with high temperature and cold acclimation. This includes temperature dose-response effects on seed germination, hypocotyl elongation, leaf development, hyponasty, rosette growth, temperature marker gene expression, stomatal conductance, chlorophyll content, ion leakage and hydrogen peroxide levels. In conclusion, thermal gradient table systems enable standardized and predictable environments to study plant responses to varying temperature regimes and can be swiftly implemented in research on temperature signalling and response.

Transcription factor OsMYB30 increases trehalose content to inhibit α-amylase and seed germination at low temperature

Low-temperature germination (LTG) is an important agronomic trait for direct-seeding cultivation of rice (Oryza sativa). Both OsMYB30 and OsTPP1 regulate the cold stress response in rice, but the function of OsMYB30 and OsTPP1 in regulating LTG and the underlying molecular mechanism remains unknown. Employing transcriptomics and functional studies revealed a sugar signaling pathway that regulates seed germination in response to low temperature (LT). Expression of OsMYB30 and OsTPP1 was induced by LT during seed germination, and overexpressing either OsMYB30 or OsTPP1 delayed seed germination and increased sensitivity to LT during seed germination. Transcriptomics and qPCR revealed that expression of OsTPP1 was upregulated in OsMYB30-overexpressing lines but downregulated in OsMYB30-knockout lines. In vitro and in vivo experiments revealed that OsMYB30 bound to the promoter of OsTPP1 and regulated the abundance of OsTPP1 transcripts. Overaccumulation of trehalose (Tre) was found in both OsMYB30- and OsTPP1-overexpressing lines, resulting in inhibition of α-amylase 1a (OsAMY1a) gene during seed germination. Both LT and exogenous Tre treatments suppressed the expression of OsAMY1a, and the osamy1a mutant was not sensitive to exogenous Tre during seed germination. Overall, we concluded that OsMYB30 expression was induced by LT to activate the expression of OsTPP1 and increase Tre content, which thus inhibited α-amylase activity and seed germination. This study identified a phytohormone-independent pathway that integrates environmental cues with internal factors to control seed germination.

Mitochondrial VOLTAGE-DEPENDENT ANION CHANNEL 3 regulates stomatal closure by abscisic acid signaling

In Arabidopsis (Arabidopsis thaliana), stomatal closure mediated by abscisic acid (ABA) is redundantly controlled by ABA receptor family proteins (PYRABACTIN RESISTANCE 1 [PYR1]/PYR1-LIKE [PYLs]) and subclass III SUCROSE NONFERMENTING 1 (SNF1)-RELATED PROTEIN KINASES 2 (SnRK2s). Among these proteins, the roles of PYR1, PYL2, and SnRK2.6 are more dominant. A recent discovery showed that ABA-induced accumulation of reactive oxygen species (ROS) in mitochondria promotes stomatal closure. By analyzing stomatal movements in an array of single and higher order mutants, we revealed that the mitochondrial protein VOLTAGE-DEPENDENT ANION CHANNEL 3 (VDAC3) jointly regulates ABA-mediated stomatal closure with a specialized set of PYLs and SnRK2s by affecting cellular and mitochondrial ROS accumulation. VDAC3 interacted with 9 PYLs and all 3 subclass III SnRK2s. Single mutation in VDAC3, PYLs (except PYR1 and PYL2), or SnRK2.2/2.3 had little effect on ABA-mediated stomatal closure. However, knocking out PYR1, PYL1/2/4/8, or SnRK2.2/2.3 in vdac3 mutants resulted in significantly delayed or attenuated ABA-mediated stomatal closure, despite the presence of other PYLs or SnRK2s conferring redundant functions. We found that cellular and mitochondrial accumulation of ROS induced by ABA was altered in vdac3pyl1 mutants. Moreover, H2O2 treatment restored ABA-induced stomatal closure in mutants with decreased stomatal sensitivity to ABA. Our work reveals that VDAC3 ensures redundant control of ABA-mediated stomatal closure by canonical ABA signaling components.

Unveiling HSP40/60/70/90/100 gene families and abiotic stress response in Jerusalem artichoke

Heat shock proteins (HSPs) are essential for plant growth, development, and stress adaptation. However, their roles in Jerusalem artichoke are largely unexplored. Using bioinformatics, we classified 143 HSP genes into distinct families: HSP40 (82 genes), HSP60 (22 genes), HSP70 (29 genes), HSP90 (6 genes), and HSP100 (4 genes). Our analysis covered their traits, evolution, and structures. Using RNA-seq data, we uncovered unique expression patterns of these HSP genes across growth stages and tissues. Notably, HSP40, HSP60, HSP70, HSP90, and HSP100 families each had specific roles. We also studied how these gene families responded to various stresses, from extreme temperatures to drought and salinity, revealing intricate expression dynamics. Remarkably, HSP40 showed remarkable flexibility, while HSP60, HSP70, HSP90, and HSP100 responded specifically to stress types. Moreover, our analysis unveiled significant correlations between gene pairs under stress, implying cooperative interactions. qRT-PCR validation underscored the significance of particular genes such as HtHSP60-7, HtHSP90-5, HtHSP100-2, and HtHSP100-3 in responding to stress. In summary, our study advances the understanding of how HSP gene families collectively manage stresses in Jerusalem artichoke. This provides insights into specific gene functions and broader plant stress responses.

Stripe Rust Effector Pst_9302 Inhibits Wheat Immunity to Promote Susceptibility

Puccinia striiformis f. sp. tritici is an obligate biotrophic fungus that causes destructive stripe rust disease in wheat. During infection, Pst secretes virulence effectors via a specific infection structure-the haustorium-inside host cells to disturb host immunity and promote fungal colonization and expansion. Hence, the identification and functional analyses of Pst effectors are of great significance in deciphering the Pst pathogenicity mechanism. Here, we identified one candidate Pst effector Pst_9302 that could suppress Bax-triggered cell death in Nicotiana benthamiana. qRT-PCR analyses showed that the transcript levels of Pst_9302 were highly increased during the early infection stages of Pst. The transient expression of Pst_9302 in wheat via the type-three secretion system (T3SS) significantly inhibited the callose deposition induced by Pseudomonas syringae EtHAn. During wheat-Pst interaction, Pst_9302 overexpression suppressed reactive oxygen species (ROS) accumulation and cell death caused by the avirulent Pst race CYR23. The host-induced gene silencing (HIGS) of Pst_9302 resulted in decreased Pst pathogenicity with reduced infection area. The results suggest that Pst_9302 plays a virulence role in suppressing plant immunity and promoting Pst pathogenicity. Moreover, wheat voltage-dependent anion channel 1 protein (TaVDAC1) was identified as candidate Pst_9302-interacting proteins by yeast two-hybrid (Y2H) screening. Pull-down assays using the His-Pst_9302 and GST-TaVDAC1 protein verified their interactions. These results suggest that Pst_9302 may modulate wheat TaVDAC1 to regulate plant immunity.

Lipidomic insights into the response of Arabidopsis sepals to mild heat stress

Arabidopsis sepals coordinate flower opening in the morning as ambient temperature rises; however, the underlying molecular mechanisms are poorly understood. Mutation of one heat shock protein encoding gene, HSP70-16, impaired sepal heat stress responses (HSR), disrupting lipid metabolism, especially sepal cuticular lipids, leading to abnormal flower opening. To further explore, to what extent, lipids play roles in this process, in this study, we compared lipidomic changes in sepals of hsp70-16 and vdac3 (mutant of a voltage-dependent anion channel, VDAC3, an HSP70-16 interactor) grown under both normal (22 °C) and mild heat stress (27 °C, mild HS) temperatures. Under normal temperature, neither hsp70-16 nor vdac3 sepals showed significant changes in total lipids; however, vdac3 but not hsp70-16 sepals exhibited significant reductions in the ratios of all detected 11 lipid classes, except the monogalactosyldiacylglycerols (MGDGs). Under mild HS temperature, hsp70-16 but not vdac3 sepals showed dramatic reduction in total lipids. In addition, vdac3 sepals exhibited a significant accumulation of plastidic lipids, especially sulfoquinovosyldiacylglycerols (SQDGs) and phosphatidylglycerols (PGs), whereas hsp70-16 sepals had a significant accumulation of triacylglycerols (TAGs) and simultaneous dramatic reductions in SQDGs and phospholipids (PLs), such as phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), and phosphatidylserines (PSs). These findings revealed that the impact of mild HS on sepal lipidome is influenced by genetic factors, and further, that HSP70-16 and VDAC3 differently affect sepal lipidomic responses to mild HS. Our studies provide a lipidomic insight into functions of HSP and VDAC proteins in the plant's HSR, in the context of floral development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00103-x.

NtHSP70-8b positively regulates heat tolerance and seed size in Nicotiana tabacum

Heat stress considerably restricts the geographical distribution of crops and affects their growth, development, and productivity. HSP70 plays a critical regulatory role in plant growth response to heat stress. However, the mechanisms of this regulatory remain poorly understood. Here, an HSP70 gene, NtHSP70-8b, which is involved in the heat stress response of tobacco, was cloned and identified. The expression of NtHSP70-8b was induced by exogenous abscisic acid (ABA) treatment and abiotic stress, including heat, drought, and salt. Notably, high NtHSP70-8b expression occurred under heat stress conditions, which was consistent with the β-glucuronidase histochemical analysis. Moreover, NtHSP70-8b overexpression markedly enhanced heat stress tolerance by changing the stomatal conductance and antioxidant capacity in tobacco leaves. qRT-PCR showed that the expression levels of ABA synthesis and response genes (NtNCED3 and NtAREB), stress defence genes (NtERD10C and NtLEA5), and other HSP genes (NtHSP90 and NtHSP26a) in NtHSP70-8b-overexpressing tobacco were high under heat stress. The interaction of NtHSP70-8b with NtHSP26a was further confirmed by a luciferase complementation imaging assay. In contrast, NtHSP70-8b knockout mutants showed significantly reduced antioxidant capacity compared to the wild type (WT) under heat stress conditions, suggesting that NtHSP70-8b acts as a positive regulator of heat stress in tobacco. Moreover, NtHSP70-8b overexpression increased the 1000-seed weight. Taken together, NtHSP70-8b is involved in the heat stress response, and NtHSP70-8b overexpression contributed to enhanced tolerance to heat stress, which is thus an essential gene with potential application value for developing heat stress-tolerant crops.

Co-application of copper oxide nanoparticles and Trichoderma harzianum with physiological, enzymatic and ultrastructural responses for the mitigation of salt stress

Chemical contamination or nutrient pollution is concerning for health, environmental, and economic reasons. Ecofriendly surface modification of nanoparticles is a consistent challenge for agricultural purposes. In response to this environmental concern, CuO-NPs synthesized through biological method using green source and characterized for morphological and structural features through SEM (scanning electron microscope) and TEM (transmission electron microscope) spectroscopy. Our research findings illustrate that the presence of salt stress induces a notable decline in both physiological and biochemical parameters within plants. Nevertheless, the utilization of T. harzianum and CuO-NPs exhibited a mitigating effect on the detrimental consequences induced by salt stress in plants. The application of T. harzianum and the simultaneous co-inoculation with CuO-NPs notably enhanced fresh biomass and facilitated vegetative growth in comparison to the control group. Furthermore, the exposure of both T. harzianum inoculum and Copper oxide nanoparticles resulted in a significant reduction of oxidative stresses, including reactive oxygen species (ROS) levels, H₂O₂, and lipid peroxidation (MDA) levels in the above-ground parts of the plant, while also minimizing electrolyte leakage (EL) by reducing root growth. Additionally, the co-inoculation of the endophyte and CuO-NPs led to a significant enhancement in antioxidant enzymatic activities, such as superoxide dismutase (SOD) and chitinase (CAT) activity in the above-ground parts, under salt stress conditions. The inoculum, along with its combination with CuO-NPs, decreased electrolyte conductivity and improved total chlorophyll contents as compared to the control. The combined application of T. harzianum and CuO-NPs improved salt tolerance in A. thaliana plants by triggering salt-associated gene expression. These findings suggest that the application of T. harzianum and CuO-NPs can considerably promote leaf anatomical changes in A. thaliana and have ability to enhance salt tolerance, particularly in saline areas.

Characterization of HSP70 family in watermelon (Citrullus lanatus): identification, structure, evolution, and potential function in response to ABA, cold and drought stress

Watermelon (Citrullus lanatus) as a crop with important economic value, is widely cultivated around the world. The heat shock protein 70 (HSP70) family in plant is indispensable under stress conditions. However, no comprehensive analysis of watermelon HSP70 family is reported to date. In this study, 12 ClHSP70 genes were identified from watermelon, which were unevenly located in 7 out of 11 chromosomes and divided into three subfamilies. ClHSP70 proteins were predicted to be localized primarily in cytoplasm, chloroplast, and endoplasmic reticulum. Two pairs of segmental repeats and 1 pair of tandem repeats existed in ClHSP70 genes, and ClHSP70s underwent strong purification selection. There were many abscisic acid (ABA) and abiotic stress response elements in ClHSP70 promoters. Additionally, the transcriptional levels of ClHSP70s in roots, stems, true leaves, and cotyledons were also analyzed. Some of ClHSP70 genes were also strongly induced by ABA. Furthermore, ClHSP70s also had different degrees of response to drought and cold stress. The above data indicate that ClHSP70s may be participated in growth and development, signal transduction and abiotic stress response, laying a foundation for further analysis of the function of ClHSP70s in biological processes.

Genomic Survey of Heat Shock Proteins in Liriodendron chinense Provides Insight into Evolution, Characterization, and Functional Diversities

Heat shock proteins (HSPs) are conserved molecular chaperones whose main role is to facilitate the regulation of plant growth and stress responses. The HSP gene family has been characterized in most plants and elucidated as generally stress-induced, essential for their cytoprotective roles in cells. However, the HSP gene family has not yet been analyzed in the Liriodendron chinense genome. In current study, 60 HSP genes were identified in the L. chinense genome, including 7 LchiHSP90s, 23 LchiHSP70s, and 30 LchiHSP20s. We investigated the phylogenetic relationships, gene structure and arrangement, gene duplication events, cis-acting elements, 3D-protein structures, protein-protein interaction networks, and temperature stress responses in the identified L. chinense HSP genes. The results of the comparative phylogenetic analysis of HSP families in 32 plant species showed that LchiHSPs are closely related to the Cinnamomum kanehirae HSP gene family. Duplication events analysis showed seven segmental and six tandem duplication events that occurred in the LchiHSP gene family, which we speculated to have played an important role in the LchiHSP gene expansion and evolution. Furthermore, the Ka/Ks analysis indicated that these genes underwent a purifying selection. Analysis in the promoter region evidenced that the promoter region LchiHSPs carry many stress-responsive and hormone-related cis-elements. Investigations in the gene expression patterns of the LchiHSPs using transcriptome data and the qRT-PCR technique indicated that most LchiHSPs were responsive to cold and heat stress. In total, our results provide new insights into understanding the LchiHSP gene family function and their regulatory mechanisms in response to abiotic stresses.

Regulation of heat shock proteins 70 and their role in plant immunity

Heat shock proteins 70 (HSP70s) are steadily gaining more attention in the field of plant biotic interactions. Though their regulation and activity in plants are much less well characterized than are those of their counterparts in mammals, accumulating evidence indicates that the role of HSP70-mediated defense mechanisms in plant cells is indispensable. In this review, we summarize current knowledge of HSP70 post-translational control in plants. We comment on the phytohormonal regulation of HSP70 expression and protein abundance, and identify a prominent role for cytokinin in HSP70 control. We outline HSP70s' subcellular localizations, chaperone activity, and chaperone-mediated protein degradation. We focus on the role of HSP70s in plant pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity, and discuss the contribution of different HSP70 subfamilies to plant defense against pathogens.

Characterization of the voltage-dependent anion channel (VDAC) gene family in wheat (Triticum aestivum L.) and its potential mechanism in response to drought and salinity stresses

Voltage-dependent anion channels (VDACs) are major transport proteins localized in the outer membrane of mitochondria and play critical roles in regulating plant growth and responding to stress. In this study, a total of 26 VDAC genes in common wheat (Triticum aestivum L.) were identified. TaVDACs that contained β-barrel structures were classified into three groups with phylogenetic and sequence alignment. Additionally, the gene structure and protein conserved motif composition varied among diverse subfamilies but were relatively conserved within the same subfamily. The basic elements that were stress- and hormone-related, including TATA-box, CAAT-box, MBS, LTR, TC-rich repeats, ABRE, P-box and TATC-box, were predicted within the promoter region of TaVDAC genes. TaVDAC expression patterns differed among tissues, organs and abiotic stress conditions. Overexpression (OE) of TaVDAC1-B conferred high tolerance to salinity and less resistance to drought stress in Arabidopsis thaliana. TaVDAC1-B interacted with Nucleoredoxin-D1 (TaNRX-D1) protein. Furthermore, compared with WT lines, salinity stress further upregulated the level of AtNRX1 (homologous gene of TaNRX-D1 in Arabidopsis) expression and the activity of superoxide dismutase in TaVDAC1-B OE lines, which led to a decrease in superoxide radical accumulation; drought stress further downregulated AtNRX1 expression and superoxide dismutase activity in TaVDAC1-B OE lines, resulting in the accumulation of superoxide radicals. Our study not only presents comprehensive information for understanding the VDAC gene family in wheat but also proposes a potential mechanism in response to drought and salinity stress.

The Role of Membrane Transporters in Plant Growth and Development, and Abiotic Stress Tolerance

The proteins of membrane transporters (MTs) are embedded within membrane-bounded organelles and are the prime targets for improvements in the efficiency of water and nutrient transportation. Their function is to maintain cellular homeostasis by controlling ionic movements across cellular channels from roots to upper plant parts, xylem loading and remobilization of sugar molecules from photosynthesis tissues in the leaf (source) to roots, stem and seeds (sink) via phloem loading. The plant's entire source-to-sink relationship is regulated by multiple transporting proteins in a highly sophisticated manner and driven based on different stages of plant growth and development (PG&D) and environmental changes. The MTs play a pivotal role in PG&D in terms of increased plant height, branches/tiller numbers, enhanced numbers, length and filled panicles per plant, seed yield and grain quality. Dynamic climatic changes disturbed ionic balance (salt, drought and heavy metals) and sugar supply (cold and heat stress) in plants. Due to poor selectivity, some of the MTs also uptake toxic elements in roots negatively impact PG&D and are later on also exported to upper parts where they deteriorate grain quality. As an adaptive strategy, in response to salt and heavy metals, plants activate plasma membranes and vacuolar membrane-localized MTs that export toxic elements into vacuole and also translocate in the root's tips and shoot. However, in case of drought, cold and heat stresses, MTs increased water and sugar supplies to all organs. In this review, we mainly review recent literature from Arabidopsis, halophytes and major field crops such as rice, wheat, maize and oilseed rape in order to argue the global role of MTs in PG&D, and abiotic stress tolerance. We also discussed gene expression level changes and genomic variations within a species as well as within a family in response to developmental and environmental cues.