Overexpression of the alfalfa DnaJ-like protein (MsDJLP) gene enhances tolerance to chilling and heat stresses in transgenic tobacco plants

Determining arsenic stress tolerance genes in rice (Oryza sativa L.) via genomic insights and QTL mapping with double haploid lines

Arsenic, a hazardous heavy metal with potent carcinogenic properties, significantly affects key rice-producing regions worldwide. In this study, we present a quantitative trait locus (QTL) mapping investigation designed to identify candidate genes responsible for conferring tolerance to arsenic toxicity in rice (Oryza sativa L.) during the seedling stage. This study identified 17 QTLs on different chromosomes, including qCHC-1 and qCHC-3 on chromosome 1 and 3 related to chlorophyll content and qRFW-12 on chromosome 12 related to root fresh weight. Gene expression analysis revealed eight candidate genes exhibited significant upregulation in the resistant lines, OsGRL1, OsDjB1, OsZIP2, OsMATE12, OsTRX29, OsMADS33, OsABCG29, and OsENODL24. These genes display sequence alignment and phylogenetic tree similarities with other species and engaging in protein-protein interactions with significant proteins. Advanced gene-editing techniques such as CRISPR-Cas9 to precisely target and modify the candidate genes responsible for arsenic tolerance will be explore. This approach may expedite the development of arsenic-resistant rice cultivars, which are essential for ensuring food security in regions affected by arsenic-contaminated soil and water.

Plastid-expressed AdDjSKI enhances photosystem II stability, delays leaf senescence, and increases fruit yield in tomato plants under heat stress

Heat stress substantially reduces tomato (Solanum lycopersicum) growth and yield globally, thereby jeopardizing food security. DnaJ proteins, constituents of the heat shock protein system, protect cells from diverse environmental stresses as HSP-70 molecular co-chaperones. In this study, we demonstrated that AdDjSKI, a serine-rich DnaJ III protein induced by pathogens, plays an important role in stabilizing photosystem II (PSII) in response to heat stress. Our results revealed that transplastomic tomato plants expressing the AdDjSKI gene exhibited increased levels of total soluble proteins, improved growth and chlorophyll content, reduced malondialdehyde (MDA) accumulation, and diminished PSII photoinhibition under elevated temperatures when compared with wild-type (WT) plants. Intriguingly, these transplastomic plants maintained higher levels of D1 protein under elevated temperatures compared with the WT plants, suggesting that overexpression of AdDjSKI in plastids is crucial for PSII protection, likely due to its chaperone activity. Furthermore, the transplastomic plants displayed lower accumulation of superoxide radical (O2 •─) and H2O2, in comparison with the WT plants, plausibly attributed to higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. This also coincides with an enhanced expression of corresponding genes, including SlCuZnSOD, SlFeSOD, SlAPX2, and SltAPX, under heat stress. Taken together, our findings reveal that chloroplastic expression of AdDjSKI in tomatoes plays a critical role in fruit yield, primarily through a combination of delayed senescence and stabilizing PSII under heat stress.

Ectopic expression of DnaJ type-I protein homolog of Vigna aconitifolia (VaDJI) confers ABA insensitivity and multiple stress tolerance in transgenic tobacco plants

Reduced crop productivity results from altered plant physiological processes caused by dysfunctional proteins due to environmental stressors. In this study, a novel DnaJ Type-I encoding gene, VaDJI having a zinc finger motif in its C-terminal domain was found to be induced early upon treatment with heat stress (within 5 min) in a heat tolerant genotype of Vigna aconitifolia RMO-40. VaDJI is induced by multiple stresses. In tobacco, ectopic expression of VaDJI reduced ABA sensitivity during seed germination and the early stages of seedling growth of transgenic tobacco plants. Concomitantly, it also improved the ability of transgenic tobacco plants to withstand drought stress by modulating the photosynthetic efficiency, with the transgenic plants having higher F_v/F_m ratios and reduced growth inhibition. Additionally, transgenic plants showed a reduced build-up of H₂O₂ and lower MDA levels and higher chlorophyll content during drought stress, which attenuated cell damage and reduced oxidative damage. An analysis using the qRT-PCR study demonstrated that VaDJI overexpression is associated with the expression of some ROS-detoxification-related genes and stress-marker genes that are often induced during drought stress responses. These findings suggest a hypothesis whereby VaDJI positively influences drought stress tolerance and ABA signalling in transgenic tobacco, and suggests that it is a potential gene for genetic improvement of drought and heat stress tolerance in crop plants.

Regulation of Heat Stress in Physcomitrium (Physcomitrella) patens Provides Novel Insight into the Functions of Plant RNase H1s

RNase H1s are associated with growth and development in both plants and animals, while the roles of RNase H1s in bryophytes have been rarely reported. Our previous data found that PpRNH1A, a member of the RNase H1 family, could regulate the development of Physcomitrium (Physcomitrella) patens by regulating the auxin. In this study, we further investigated the biological functions of PpRNH1A and found PpRNH1A may participate in response to heat stress by affecting the numbers and the mobilization of lipid droplets and regulating the expression of heat-related genes. The expression level of PpRNH1A was induced by heat stress (HS), and we found that the PpRNH1A overexpression plants (A-OE) were more sensitive to HS. At the same time, A-OE plants have a higher number of lipid droplets but with less mobility in cells. Consistent with the HS sensitivity phenotype in A-OE plants, transcriptomic analysis results indicated that PpRNH1A is involved in the regulation of expression of heat-related genes such as DNAJ and DNAJC. Taken together, these results provide novel insight into the functions of RNase H1s.

Genome-Wide Identification and Characterization of DnaJ Gene Family in Grape (Vitis vinifera L.)

Grape production in southern China suffers great loss due to various environmental stresses. To understand the mechanism of how the grape plants respond to these stresses is an active area of research in developing cultivation techniques. Plant stress resistance is known to rely on special proteins. Amongst them, DnaJ protein (HSP40) serves as co-chaperones of HSP70, playing crucial roles in various stress response. However, the DnaJ proteins encoded by the DnaJ gene family in Vitis vinifera L. have not been fully described yet. In this study, we identified 78 VvDnaJs in the grape genome that can be classified into three groups—namely, DJA, DJB, and DJC. To reveal the evolutionary and stress response mechanisms for the VvDnaJ gene family, their evolutionary and expression patterns were analyzed using the bioinformatic approach and qRT-PCR. We found that the members in the same group exhibited a similar gene structure and protein domain organization. Gene duplication analysis demonstrated that segmental and tandem duplication may not be the dominant pathway of gene expansion in the VvDnaJ gene family. Codon usage pattern analysis showed that the codon usage pattern of VvDnaJs differs obviously from the monocotyledon counterparts. Tissue-specific analysis revealed that 12 VvDnaJs present a distinct expression profile, implying their distinct roles in various tissues. Cis-acting element analysis showed that almost all VvDnaJs contained the elements responsive to either hormones or stresses. Therefore, the expression levels of VvDnaJs subjected to exogenous hormone applications and stress treatments were determined, and we found that VvDnaJs were sensitive to hormone treatments and shade, salt, and heat stresses, especially VIT_00s0324g00040. The findings of this study could provide comprehensive information for the further investigation on the genetics and protein functions of the DnaJ gene family in grape.

Ultraviolet-B exposure and exogenous hydrogen peroxide application lead to cross-tolerance toward drought in Nicotiana tabacum L

Acclimation of plants to water deficit involves biochemical and physiological adjustments. Here, we studied how ultraviolet (UV)-B exposure and exogenously applied hydrogen peroxide (H2 O2 ) potentiates drought tolerance in tobacco (Nicotiana tabacum L. cv. xanthi nc). Separate and combined applications for 14 days of 1.75 kJ m-2  day-1 UV-B radiation and 0.2 mM H2 O2 were assessed. Both factors, individually and combined, resulted in inhibition of growth. Furthermore, the combined treatment led to the most compacted plants. UV-B- and UV-B + H2 O2 -treated plants increased total antioxidant capacity and foliar epidermal flavonol index. H2 O2 - and UV-B + H2 O2 -pre-treated plants showed cross-tolerance to a subsequent 7-day moderate drought treatment, which was assessed as the absence of negative impact on growth, leaf wilting, and leaf relative water content. Plant responses to the pre-treatment were notably different: (1) H2 O2 increased the activity of catalase (EC 1.11.1.6), phenylalanine ammonia lyase (EC 4.3.1.5), and peroxidase activities (EC 1.11.1.7), and (2) the combined treatment induced epidermal flavonols which were key to drought tolerance. We report synergistic effects of UV-B and H2 O2 on transcription accumulation of UV RESISTANCE LOCUS 8, NAC DOMAIN PROTEIN 13 (NAC13), and BRI1-EMS-SUPPRESSOR 1 (BES1). Our data demonstrate a pre-treatment-dependent response to drought for NAC13, BES1, and CHALCONE SYNTHASE transcript accumulation. This study highlights the potential of combining UV-B and H2 O2 to improve drought tolerance which could become a useful tool to reduce water use.

Overexpression of EcDREB2A transcription factor from finger millet in tobacco enhances tolerance to heat stress through ROS scavenging

An extreme temperature regime beyond desired level imposes significant stress in crop plants. The low and high temperature stresses are one of the primary constraints for plant development and yield. Finger millet, being a climate resilient crop, is a potential source of novel stress tolerant genes. In this study, functional characterization of finger millet DREB2A gene in different abiotic stress conditions was done. This novel EcDREB2A transcription factor isolated from finger millet is a truncated version of DREB2A gene compared to previously reported DREB genes from other plant species. The overexpression of EcDREB2A in transgenic tobacco exhibits improved tolerance against heat stress 42 °C for up to 7 days, by altering physiology and biochemical means. However, same transgenic lines were unable to provide tolerance to 200 mM NaCl and 200 mM Mannitol stress. Under heat stress conditions, increased seed germination with improved lateral roots, fresh and dry weight relative to wild type (WT) was observed. The EcDREB2A transgenics exposed to heat stress showed improved rate of stomatal conductance, chlorophyll and carotenoids contents, and other photosynthesis parameters compared to WT plants. EcDREB2A overexpression also resulted in increased antioxidant enzyme activity (SOD, CAT, GR, POD and, APX) with decreased electrolyte leakage (EL), H2O2, and malondialdehyde (MDA) content than WT plants under heat stress. Quantitative real time expression analysis demonstrated that all eight downstream genes were significantly upregulated in transgenic plants only after heat stress. Our data provide a clear demonstration of the positive impact of overexpression of EcDREB2A providing heat stress tolerance to plants.

Functional analysis of tomato CHIP ubiquitin E3 ligase in heat tolerance

Plants have evolved genetic and physiological mechanisms to mitigate the adverse effects of high temperature. CARBOXYL TERMINUS OF THE HSC70-INTERACTING PROTEINS (CHIP) is a conserved chaperone-dependent ubiquitin E3 ligase that targets misfolded proteins. Here, we report functional analysis of the SlCHIP gene from tomato (Solanum lycopersicum) in heat tolerance. SlCHIP encodes a CHIP protein with three tandem tetracopeptide repeat (TPR) motifs and a C-terminal U box domain. Phylogenetic analysis of CHIP homologs from animals, spore-bearing and seed plants revealed a tree topology similar to the evolutionary tree of the organisms. Expression of SlCHIP was induced under high temperature and was also responsive to plant stress hormones. Silencing of SlCHIP in tomato reduced heat tolerance based on increased heat stress symptoms, reduced photosynthetic activity, elevated electrolyte leakage and accumulation of insoluble protein aggregates. The accumulated protein aggregates in SlCHIP-silenced plants were still highly ubiquitinated, suggesting involvement of other E3 ligases in ubiquitination. SlCHIP restored the heat tolerance of Arabidopsis chip mutant to the wild type levels. These results indicate that tomato SlCHIP plays a critical role in heat stress responses most likely by targeting degradation of misfolded proteins that are generated during heat stress.

Sulfur triggers glutathione and phytochelatin accumulation causing excess Cd bound to the cell wall of roots in alleviating Cd-toxicity in alfalfa

Although Cd is threatening to the environment, animal, and human, the eco-friendly approach to mitigate the Cd-toxicity in alfalfa was barely studied. Therefore, this study aims at elucidating the role of S, a crucial macroelement, in alleviating Cd toxicity in alfalfa plants. The supplementation of S in Cd-stressed alfalfa reversed the detrimental effect on plant biomass, chlorophyll synthesis, and protein concentration. Interestingly, S surplus restored the photosynthetic kinetics, such as Fv/Fm, Pi_ABS, and Mo values in leaves of Cd-stressed alfalfa. Further, Cd-induced adverse effect on membrane stability, cell viability, and redox status was restored due to S under Cd stress. The exogenous S not only increased S status and the expression of sulfate transporters (MsSULRT1;2 and MsSULTR1;3), but also decreased the Cd concentration in the shoot by retaining elevated Cd in root tissue. Further analysis revealed the upregulation of MsGS (glutathione synthetase) and MsPCS1 (phytochelatin synthase) genes along with the increased concentration of glutathione and phytochelatin, predominantly in roots subjected to S surplus under Cd stress. The subcellular Cd analysis showed elevated Cd in the cell wall but not in the vacuole. It suggests that S-induced elevated glutathione enables the phytochelatin to bind with excess Cd leading to subcellular sequestration in the cell wall of roots. Also, S stimulates the S-metabolites and GR enzyme that coordinately counteracts Cd-induced oxidative damage. These findings can be utilized to popularize the application of S and to perform breeding/transgenic experiments to develop Cd-free forage crops.

Identification of key genes and modules in response to Cadmium stress in different rice varieties and stem nodes by weighted gene co-expression network analysis

Soil cadmium (Cd) pollution threatens food safety. This study aimed to identify genes related to Cd accumulation in rice. Low- (Shennong 315, short for S315) and high- (Shendao 47, short for S47) Cd-accumulative rice cultivars were incubated with CdCl₂·2.5H₂O. RNA-seq and weighted gene co-expression network analysis (WGCNA) were performed to identify the modules and genes associated with Cd-accumulative traits of rice. After Cd stress treatment, the Cd content in various tissues of S315 was significantly higher than that of S47. In the stem nodes, the Cd distribution results of the two varieties indicated that the unelongated nodes near the root (short for node A) had a stronger ability to block Cd transfer upwards than the panicle node (short for node B). Cd stress induced huge changes in gene expression profiles. After analyzing the differentially expressed genes (DEGs) in significantly correlated WGCNA modules, we found that genes related to heavy metal transportation had higher expression levels in node A than that in node B, such as Copper transporter 6 (OS04G0415600), Zinc transporter 10 (OS06G0566300), and some heavy-metal associated proteins (OS11G0147500, OS03G0861400, and OS10G0506100). In the comparison results between S315 and S47, the expression of chitinase (OS03G0679700 and OS06G0726200) was increased by Cd treatment in S315. In addition, OsHSPs (OS05G0460000, OS08G0500700), OsHSFC2A (OS02G0232000), and OsDJA5 (OS03G0787300) were found differentially expressed after Cd treatment in S315, but changed less in S47. In summary, different rice varieties have different processes and intensities in response to Cd stress. The node A might function as the key tissue for blocking Cd upward transport into the panicle via vigorous processes, including of heavy metal transportation, response to stress, and cell wall.

Hsp40 Protein LeDnaJ07 Enhances the Thermotolerance of Lentinula edodes and Regulates IAA Biosynthesis by Interacting LetrpE

Our previous study found that LeDnaJ07 RNAi decreased Lentinula edodes resistance to heat stress and Trichoderma atroviride infection. In this study, the structure and function of the LeDnaJ07 gene was analyzed by gene cloning and overexpression in L. edodes stress-sensitive strain YS55 via the Agrobacterium-mediated transformation method. Transformants were confirmed by qRT-PCR, fluorescence observation and Southern blotting. Overexpression of LeDnaJ07 in YS55 not only enhanced L. edodes mycelial resistance to heat stress but also facilitated mycelial growth. In the presence of heat stress, the intracellular IAA content showed a significant increase in the two LeDnaJ07 overexpression strains but only a slight change in the YS55 wild type strain. Moreover, the interaction between LeDnaJ07 and LetrpE was demonstrated via Y2H and BiFC assays. These results suggested that LeDnaJ07 may be involved in regulating IAA biosynthesis and the resistance of L. edodes to heat stresses via interacting with LetrpE.

Response of transgenic tobacco overexpressing the CchGLP gene to cadmium and aluminium: phenotypic and microRNAs expression changes

Transgenic tobacco (N. tabacum cv. Xanthi nc) expressing Capsicum chinense CchGLP gene that encodes an Mn-SOD, constitutively produces hydrogen peroxide that increase endogenous ROS levels. Previous studies using these plants against geminivirus infections as well as drought stress confirmed that CchGLP expression conferred resistance against biotic and abiotic stresses. Cadmium (Cd) and Aluminium (Al) contamination in soils are a major ecological concern since they are two of the most widespread toxic elements in terrestrial environments. Trying to explore additional possible tolerance to another stresses in these plants, the aim of this work was to analyse the response to cadmium and aluminium salts during germination and early stages of plantlet development and a differential transcriptome of microRNAs (miRNAs) expression in expressing CchGLP transgenic lines and an azygote non-CchGLP expressing line. Plants were grown in vitro with addition of CdCl₂ and AlCl₃ at three different concentrations: 100, 300 and 500 μM and 50, 150 and 300 μM, respectively. The results showed higher tolerance to Cd and Al salts evaluated in two CchGLP-expressing transgenic lines L8 and L26 in comparison with the azygous non-CchGLP expressing line L1. Interestingly, L8 under Al stress presented vigorous roots and development of radicular hairs in comparison with azygous control (L1). Differentially expressed miRNAs in the comparison between L8 and L1 were associated with up and down-regulation of target genes related with structural molecule activity and ribosome constituents, as well as down-regulation in proton-transporting V-type ATPase (Vacuolar ATPase or V-ATPase). Moreover, KEGG analysis of the target genes for the differentially expressed miRNAs, led to identification of genes related with metabolic pathways and biosynthesis of secondary metabolites. One possible explanation of the tolerance to Cd and Al displayed in the transgenic tobaccos evaluated, might involve the fact that several down-regulated miRNAs, were found associated with target genes expressing V-ATPase. Specifically, miR7904-5p was down regulated and related with the up-regulation of one V-ATPase. The expression levels of these genes was confirmed by qRT-PCR assays, thus suggesting that a cation transport activity driven by the V-ATPases-dependent proton motive force, might significantly contribute as one mechanism for Cd and Al detoxification by vacuolar compartmentation in these transgenic tobacco plants.

In-silico prediction of novel genes responsive to drought and salinity stress tolerance in bread wheat (Triticum aestivum)

Common wheat (Triticum aestivum) is the most widely grown cereal crop and is cultivated extensively in dry regions. Water shortage, resulting from either drought or salinity, leads to slow growth and loss of wheat yield. In order to predict new genes responsive to the drought and salt stresses in wheat, 6,717 expressed sequence tags (ESTs), expressed in drought and salinity stress conditions were collected from the National Center for Biotechnology Information (NCBI). The downloaded ESTs were clustered and assembled into 354 contigs; 14 transcription factor families in 29 contigs were identified. In addition, 119 contigs were organized in five enzyme classes. Biological functions were obtained for only 324 of the 354 contigs using gene ontology. In addition, using Kyoto Encyclopedia of Genes and Genomes database, 191 metabolic pathways were identified. The remaining contigs were used for further analysis and the search for new genes responsive to drought and salt stresses. These contigs were mapped on the International Wheat Genome Sequencing Consortium RefSeq v1.0 assembly, the most complete version of the reference sequence of the bread wheat variety Chinese Spring. They were found to have from one to three locations on the subgenomes A, B, and D. Full-length gene sequences were designed for these contigs, which were further validated using promoter analysis. These predicted genes may have applications in molecular breeding programs and wheat drought and salinity research.

Genome-wide analysis of the rice J-protein family: identification, genomic organization, and expression profiles under multiple stresses

J-proteins which function as molecular chaperone played critical roles in plant growth, development, and response to various environment stresses, but little was reported on this gene family in rice. Here, we identified 115 putative rice J-proteins and classified them into nine major clades (I–IX) according to their phylogenetic relationships. Gene-structure analysis revealed that each member of the same clade has same or similar exon–intron structure, and most rice J-protein genes of clade VII were intronless. Chromosomes mapping suggested that tandem duplication was occurred in evolution. Expression profile showed that the 61 rice J-protein genes were expressed in at least one tissue. The result implied that they could be involved in the process of rice growth and development. The RNA-sequencing data identified 96 differentially expressed genes, 59.38% (57/96), 67.71% (65/96), and 62.50% (60/96) genes were induced by heat stress, drought stress, and salt stress, respectively. The results indicated that J-protein genes could participated in rice response to different stresses. The findings in this study would provide a foundation for further analyzing the function of J-proteins in rice.