CC-type glutaredoxin, MeGRXC3, associates with catalases and negatively regulates drought tolerance in cassava (Manihot esculenta Crantz)

The function of CC-type glutaredoxins in salt-induced flower drop in tomato

Salt stress significantly induces the abscission of flowers and fruits, resulting in a reduction in crop yields and posing a threat to food security. Nonetheless, the molecular mechanisms underlying the abscission triggered by salt stress remain poorly understood. In our study, the effects of different NaCl concentrations on the growth of tomato plants and flower drop were investigated. The results showed that 200 mM NaCl inhibited the growth of tomato plants and accelerated the flower drop of tomato plants. Through an RNA-Seq assay, differentially expressed genes (DEGs) in the abscission zone (AZ) under control and salt stress treatment conditions were screened. Among DEGs, the reactive oxygen species (ROS)-related pathway was the most significantly enriched pathway in the gene ontology (GO) analysis, which was consistent with the increase in ROS content in the AZ under salt treatment. Salt stress significantly induced the expression of CC-type SlGRXs in the AZ. Overexpression of SlGRX16 significantly inhibited the content of ROS in AZ and salt stress-induced flower drop. These results provide new insights and basic data for understanding the mechanisms of salt-stress-induced flower drop.

Interacting MeZFP29 and MebZIPW regulates MeNRT2.2 from cassava responding to nitrate signaling

KEY MESSAGE

Cassava is a significant tropical cash crop. MeZFP29 interacting with MebZIPW improves MeNRT2.2, encoding a high-affinity nitrate transporter, through binding to NREs under low nitrate and shows a nitrate-signaling-triggered regulation. Cassava (Manihot esculenta) is a globally significant tropical root crop and exhibits exceptional adaptability to native soil fertility. MeNRT2.2 encodes a high-affinity nitrate transporter in cassava and heterologous overexpression of MeNRT2.2 in Arabidopsis increases nitrate transportation and utilization under nitrogen scarcity. However, the responsive mechanism of MeNRT2.2 to nitrate remains unclear. In this study, we identified a nitrate-responsive fragment of 450 bp located upstream of the start codon of MeNRT2.2, and two potential regulators, MeZFP29 and MebZIPW, of MeNRT2.2. Two regulators specifically bound to nitrate-responsive cis-element (NRE), i.e., TGCATT and CAGATG, in the 450 bp fragment and together significantly stimulated promoter activity. Furthermore, we confirmed the interaction between two regulators in vivo and in vitro via Y2H, BiFC, Co-IP, and GST-pull-down assays. In addition, the distribution of MeZFP29 and its heterodimers (MeZFP&MebZIPW) are determined by nitrate signaling, i.e., in the cytoplasm and nucleus under nitrogen limitation, and predominantly in nucleus under sufficient nitrate. In contrast, MebZIPW consistently localizes to the cytoplasm and nucleus regardless of nitrate conditions. Moreover, overexpression of MeZFP29 in Arabidopsis enhanced growth and chlorophyll content, particularly, under low nitrate conditions, while MebZIPW did not. These findings not only confirm the regulation of MeZFP29 and MebZIPW on MeNRT2.2, but also illustrate the nitrate signaling-triggered promotion and feedback on MeNRT2.2. Our study provides a novel approach to enhancing nitrogen-use efficiency in cassava by modulating the regulators under moderate nitrogen levels as low as possible.

CmTGA8-CmAPX1/CmGSTU25 regulatory model involved in trehalose induced cold tolerance in oriental melon seedlings

Plants have developed complex regulatory networks to adapt to various stresses, including cold stress. Trehalose (Tre), known as the "sugar of life," plays a crucial role in enhancing cold tolerance by triggering antioxidation. However, the underlying regulatory mechanisms remain unclear. This study examines the transcription factor gene CmTGA8, which is induced by Tre under normal and cold conditions in melon seedlings (Cucumis melo L.), through transcriptome analysis and RT-qPCR. Reverse genetic analyses showed that silencing CmTGA8 reduced ascorbate peroxidase (APX) and glutathione S-transferase (GST) activities, suppressed CmAPX1 and CmGSTU25 expression, and increased cold susceptibility in melon seedlings. Our previous reports illustrated that Tre treatment significantly induced the expression of respiratory burst oxidase homologues (CmRBOHD) gene, encoding NADPH oxidases responsible for generating apoplastic H2O2. Silencing CmRBOHD markedly inhibited CmTGA8, CmAPX1, and CmGSTU25 expression and reduced cold tolerance. Moreover, H2O2 treatment upregulated CmTGA8 expression, while the NADPH oxidase inhibitor diphenyleneiodonium (DPI) treatment downregulated it. Additionally, CmTGA8 physically interacted with CmAPX1 and CmGSTU25 to promote their expression. Silencing CmGSTU25 decreased GST activity and ferric reducing ability of plasma (FRAP), further increasing cold sensitivity. These findings identify a novel regulatory hierarchy of the H2O2-CmTGA8-CmAPX1/CmGSTU25 cascade in the Tre-mediated cold response pathway in melon seedlings.

Genome-wide characterization and expression profiling of the TGA gene family in sweet orange (Citrus sinensis) reveal CsTGA7 responses to multiple phytohormones and abiotic stresses

Citrus is widely recognized as one of the most economically important fruit crops worldwide. However, citrus growth is frequently hindered by external environmental stresses, which severely limit its development and yield. The TGA (TGACG motif-binding factor) transcription factors (TFs) are members of the bZIP family and play essential roles in plant defense responses and organ development. Nevertheless, the systematic identification and functional analysis of the TGA family in citrus remains unreported. In this study, genome-wide analysis identified a total of seven CsTGA TFs in Citrus sinensis, which were classified into five subgroups. Phylogenetic and syntenic analysis revealed that the CsTGA genes are highly conserved, with no tandem or segmental duplication events among family members. Promoter sequence analysis identified numerous cis-acting elements associated with transcriptional regulation, phytohormone response, and environmental adaptation in the promoters of CsTGA genes. The expression patterns under five phytohormones and three abiotic stresses demonstrated significant responses of multiple CsTGA genes under various forms of adversity. Among all tested treatments, CsTGA7 showed the most robust response to multiple stresses. Tissue-specific expression pattern analysis revealed potential functional biases among CsTGA genes. In-depth analysis showed that CsTGA7 localized in the nucleus and possessed transcriptional activation activity, consistent with the typical characteristic of transcriptional regulators. In summary, our research systematically investigated the genomic signature of the TGA family in C. sinensis and unearthed CsTGA7 with potential functions in phytohormone signaling transduction and abiotic stress responses. Our study establishes a basis for further exploration of the function of CsTGA genes under abiotic stress.

Divergent Photosynthetic Strategies of Lupinus polyphyllus and Helleborus viridis During Cold Acclimation and Freezing-Thaw Recovery

Low temperatures can significantly affect the growth of ornamental plants, emphasizing the importance of improving their cold tolerance. However, comparative studies on the photosynthetic responses of sun and shade plants to low temperatures remain limited. In this study, gas exchange, chlorophyll fluorescence in Photosystem II (PSII) and Photosystem I (PSI), the antioxidant system, the osmoregulator substance, and lipid peroxidation were investigated in the shade plant Helleborus viridis (Hv) and the sun plant Lupinus polyphyllus (Lp) during cold acclimation (CA) and the freezing-thaw recovery (FTR). The CA treatment significantly declined the net photosynthetic rate (Pn) and the maximum photochemical efficiency of PSII (Fv/Fm) in Hv and Lp, indicating the photoinhibition occurred in both species. However, Hv exhibited a much better photosynthetic stability to maintain Pn, Fv/Fm, and carboxylation efficiency (CE) than Lp during CA, suggesting that Hv had a greater photosynthetic resilience compared to Lp. Furthermore, Hv preferred to maintain Pn, Fv/Fm, the actual photosynthetic efficiency of PSII (Y(II)), and the actual photosynthetic efficiency of PSI (Y(I)) to consistently provide the necessary energy for the carbon assimilation process, while Lp tended to divert and dissipate excess energy by thermal dissipation and cyclic electron flow during CA. Moreover, there were higher soluble sugar contents in Hv in comparison to Lp. These traits allowed Hv to recover photosynthetic efficiency and maintain cellular integrity better than Lp after the freezing stress. In conclusion, CA significantly reduced the photosynthetic capacity and led to the divergent photosynthetic strategies of both species, which finally resulted in a different freezing tolerance after the freezing-thaw recovery. These findings provide insights into the divergent photoprotective strategies of sun and shade plants in response to cold temperatures.

MdMYB54 reduces disease severity caused by Fusarium solani in apple by modulating cell wall cellulose and pectate lyase-dependent defense

The plant cell wall is the first barrier against pathogen invasion. Fusarium solani is the primary pathogen responsible for apple replant disease. In this study, we identified an MYB protein, MdMYB54, which interacts with the positive regulator of F. solani resistance, MdERF114, and confers apple-increased tolerance against F. solani. The cellulose synthetase (CESA) gene MdCesA6 and pectin lyase-like (PLL) genes MdPLL8 and MdPLL12 were screened as three potential downstream target genes of MdMYB54 using DAP-seq. The results of electrophoretic mobility shift and yeast one-hybrid assays showed that MdMYB54 directly binds to the promoters of MdCesA6, MdPLL8, and MdPLL12 in vivo and in vitro. Dual-luciferase and β-glucuronidase assays showed that MdMYB54 activates the expression of these genes. The cellulose content and pectin lyase activity of MdMYB54-overexpressed roots were significantly higher than those of wild-type plants under F. solani treatment but were the opposite in MdMYB54-RNAi roots. The deposition of cellulose enhanced the physical barrier of the plant cell wall, whereas the activation of pectin lyase promoted the formation of oligogalacturonides and the production of reactive oxygen species. Overexpression of MdCesA6, MdPLL8, and MdPLL12 in the root system enhanced the tolerance of apple to F. solani. The direct interaction of MdERF114 with MdMYB54 enhanced MdMYB54-mediated cell wall defense response. These results suggest that modifying these candidate genes may provide a strategy for improving the resistance of apple to F. solani.

The regulation mechanism of ethephon-mediated delaying of postharvest physiological deterioration in cassava storage roots based on quantitative acetylproteomes analysis

Ethylene plays diverse roles in post-harvest processes of horticultural crops. However, its impact and regulation mechanism on the postharvest physiological deterioration (PPD) of cassava storage roots is unknown. In this study, a notable delay in PPD of cassava storage roots was observed when ethephon was utilized as an ethylene source. Physiological analyses and quantitative acetylproteomes were employed to investigate the regulation mechanism regulating cassava PPD under ethephon treatment. Ethephon was found to enhance the reactive oxygen species (ROS) scavenging system, resulting in a significant decrease in H2O2 and malondialdehyde (MDA) content. The comprehensive acetylome analysis identified 12,095 acetylation sites on 4403 proteins. Subsequent analysis demonstrated that ethephon can regulate the acetylation levels of antioxidant enzymes and members of the energy metabolism pathways. In summary, ethephon could enhance the antioxidant properties and regulate energy metabolism pathways, leading to the delayed PPD of cassava.

PoWRKY69-PoVQ11 module positively regulates drought tolerance by accumulating fructose in Paeonia ostii

Drought is a detrimental environmental factor that restricts plant growth and threatens food security throughout the world. WRKY transcription factors play vital roles in abiotic stress response. However, the roles of IIe subgroup members from WRKY transcription factor family in soluble sugar mediated drought response are largely elusive. In this study, we identified a drought-responsive IIe subgroup WRKY transcription factor, PoWRKY69, from Paeonia ostii. PoWRKY69 functioned as a positive regulator in response to drought stress with nucleus expression and transcriptional activation activity. Silencing of PoWRKY69 increased plants sensitivity to drought stress, whereas conversely, overexpression of PoWRKY69 enhanced drought tolerance in plants. As revealed by yeast one-hybrid, electrophoretic mobility shift assay, and luciferase reporter assays, PoWRKY69 could directly bind to the W-box element of fructose-1,6-bisphosphate aldolase 5 (PoFBA5) promoter, contributing to a cascade regulatory network to activate PoFBA5 expression. Furthermore, virus-induced gene silencing and overexpression assays demonstrated that PoFBA5 functioned positively in response to drought stress by accumulating fructose to alleviate membrane lipid peroxidation and activate antioxidant defense system, these changes resulted in reactive oxygen species scavenging. According to yeast two-hybrid, bimolecular fluorescence complementation, and firefly luciferase complementation imaging assays, valine-glutamine 11 (PoVQ11) physically interacted with PoWRKY69 and led to an enhanced activation of PoWRKY69 on PoFBA5 promoter activity. This study broadens our understanding of WRKY69-VQ11 module regulated fructose accumulation in response to drought stress and provides feasible molecular measures to create novel drought-tolerant germplasm of P. ostii.

An evolutionary view of the function of CC-type glutaredoxins in plant development and adaptation to the environment

Land plants have to face an oxidizing, heterogeneous, and fast changing environment. Redox-dependent post-translational modifications emerge as a critical component of plant responses to stresses. Among the thiol oxidoreductase superfamily, class III CC-type glutaredoxins (called ROXYs) are land plant specific, and their evolutionary history is highly dynamic. Angiosperms encode many isoforms, classified into five subgroups (Aα, Aβ, Bα, Bβ, Bγ) that probably evolved from five common ancestral ROXYs, with higher evolutionary dynamics in the Bγ subgroup compared with the other subgroups. ROXYs can modulate the transcriptional activity of TGA transcription factor target genes, although their biochemical function is still debated. ROXYs participate in the control of proper plant development and reproduction, and are mainly negative regulators of plant responses to biotic and abiotic stresses. This suggests that most ROXYs could play essential and conserved functions in resetting redox-dependent changes in transcriptional activity upon stress signaling to ensure the responsiveness of the system and/or avoid exaggerated responses that could lead to major defects in plant growth and reproduction. In Arabidopsis Bγ members acquired important functions in responses to nitrogen availability and endogenous status, but the rapid and independent evolution of this subclass might suggest that this function results from neofunctionalization, specifically observed in core eudicots.

Influence of Drought Stress on the Rhizosphere Bacterial Community Structure of Cassava (Manihot esculenta Crantz)

Drought presents a significant abiotic stress that threatens crop productivity worldwide. Rhizosphere bacteria play pivotal roles in modulating plant growth and resilience to environmental stresses. Despite this, the extent to which rhizosphere bacteria are instrumental in plant responses to drought, and whether distinct cassava (Manihot esculenta Crantz) varieties harbor specific rhizosphere bacterial assemblages, remains unclear. In this study, we measured the growth and physiological characteristics, as well as the physical and chemical properties of the rhizosphere soil of drought-tolerant (SC124) and drought-sensitive (SC8) cassava varieties under conditions of both well-watered and drought stress. Employing 16S rDNA high-throughput sequencing, we analyzed the composition and dynamics of the rhizosphere bacterial community. Under drought stress, biomass, plant height, stem diameter, quantum efficiency of photosystem II (Fv/Fm), and soluble sugar of cassava decreased for both SC8 and SC124. The two varieties' rhizosphere bacterial communities' overall taxonomic structure was highly similar, but there were slight differences in relative abundance. SC124 mainly relied on Gamma-proteobacteria and Acidobacteriae in response to drought stress, and the abundance of this class was positively correlated with soil acid phosphatase. SC8 mainly relied on Actinobacteria in response to drought stress, and the abundance of this class was positively correlated with soil urease and soil saccharase. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of cassava to drought stress and clarified that this process is significantly related to variety.

CPK1-HSP90 phosphorylation and effector XopC2-HSP90 interaction underpin the antagonism during cassava defense-pathogen infection

Cassava is one of the most important tropical crops, but it is seriously affected by cassava bacteria blight (CBB) caused by the bacterial pathogen Xanthomonas phaseoli pv manihotis (Xam). So far, how pathogen Xam infects and how host cassava defends during pathogen-host interaction remains elusive, restricting the prevention and control of CBB. Here, the illustration of HEAT SHOCK PROTEIN 90 kDa (MeHSP90.9) interacting proteins in both cassava and bacterial pathogen revealed the dual roles of MeHSP90.9 in cassava-Xam interaction. On the one hand, calmodulin-domain protein kinase 1 (MeCPK1) directly interacted with MeHSP90.9 to promote its protein phosphorylation at serine 175 residue. The protein phosphorylation of MeHSP90.9 improved the transcriptional activation of MeHSP90.9 clients (SHI-RELATED SEQUENCE 1 (MeSRS1) and MeWRKY20) to the downstream target genes (avrPphB Susceptible 3 (MePBS3) and N-aceylserotonin O-methyltransferase 2 (MeASMT2)) and immune responses. On the other hand, Xanthomonas outer protein C2 (XopC2) physically associated with MeHSP90.9 to inhibit its interaction with MeCPK1 and the corresponding protein phosphorylation by MeCPK1, so as to repress host immune responses and promote bacterial pathogen infection. In summary, these results provide new insights into genetic improvement of cassava disease resistance and extend our understanding of cassava-bacterial pathogen interaction.

Pan-transcriptomic analysis reveals alternative splicing control of cold tolerance in rice

Plants have evolved complex mechanisms to adapt to harsh environmental conditions. Rice (Oryza sativa) is a staple food crop that is sensitive to low temperatures. However, its cold stress responses remain poorly understood, thus limiting possibilities for crop engineering to achieve greater cold tolerance. In this study, we constructed a rice pan-transcriptome and characterized its transcriptional regulatory landscape in response to cold stress. We performed Iso-Seq and RNA-Seq of 11 rice cultivars subjected to a time-course cold treatment. Our analyses revealed that alternative splicing-regulated gene expression plays a significant role in the cold stress response. Moreover, we identified CATALASE C (OsCATC) and Os03g0701200 as candidate genes for engineering enhanced cold tolerance. Importantly, we uncovered central roles for the 2 serine-arginine-rich proteins OsRS33 and OsRS2Z38 in cold tolerance. Our analysis of cold tolerance and resequencing data from a diverse collection of 165 rice cultivars suggested that OsRS2Z38 may be a key selection gene in japonica domestication for cold adaptation, associated with the adaptive evolution of rice. This study systematically investigated the distribution, dynamic changes, and regulatory mechanisms of alternative splicing in rice under cold stress. Overall, our work generates a rich resource with broad implications for understanding the genetic basis of cold response mechanisms in plants.

Cassava phosphatase PP2C1 modulates thermotolerance via fine-tuning dephosphorylation of antioxidant enzymes

Global warming is an adverse environmental factor that threatens crop yields and food security. 2C-type protein phosphatases (PP2Cs), as core protein phosphatase components, play important roles in plant hormone signaling to cope with various environmental stresses. However, the function and underlying mechanism of PP2Cs in the heat stress response remain elusive in tropical crops. Here, we report that MePP2C1 negatively regulated thermotolerance in cassava (Manihot esculenta Crantz), accompanied by the modulation of reactive oxygen species (ROS) accumulation and the underlying antioxidant enzyme activities of catalase (CAT) and ascorbate peroxidase (APX). Further investigation found that MePP2C1 directly interacted with and dephosphorylated MeCAT1 and MeAPX2 at serine (S) 112 and S160 residues, respectively. Moreover, in vitro and in vivo assays showed that protein phosphorylation of MeCAT1S112 and MeAPX2S160 was essential for their enzyme activities, and MePP2C1 negatively regulated thermotolerance and redox homeostasis by dephosphorylating MeCAT1S112 and MeAPX2S160. Taken together, this study illustrates the direct relationship between MePP2C1-mediated protein dephosphorylation of MeCAT1 and MeAPX2 and ROS accumulation in thermotolerance to provide insights for adapting to global warming via fine-tuning thermotolerance of the tropical crop cassava.

Molecular identification and functional characterization of an environmental stress responsive glutaredoxin gene ROXY1 in Quercus glauca

Quercus glauca is a valuable natural resource with both economic and ecological values. It is one of the dominant forest tree species widely distributed in Southern China. As a perennial broadleaf plant, Q. glauca inevitably encounters numerous stresses from environment. Glutaredoxins (GRXs) are a kind of small oxidoreductases that play an important role in response to oxidative stress. CC-type GRXs also known as ROXYs are specific to land plants. In this study, we isolated a CC-type GRX gene, QgROXY1, from Q. glauca. Expression of QgROXY1 is induced by a variety of environmental stimuli. QgROXY1 protein localizes to both cytoplasm and nucleus; whereas the nucleus localized QgROXY1 could physically interact with the basic region/leucine zipper motif (bZIP) transcription factor AtTGA2 from Arabidopsis thaliana. Transgenic A. thaliana ectopically expressing QgROXY1 is hypersensitive to exogenously applied salicylic acid. Induction of plant defense gene is significantly impaired in QgROXY1 transgenic plants that results in enhanced susceptibility to infection of Botrytis cinerea pathogen, indicating the evolutionary conserved function among ROXY homologs in weedy and woody plants. This is the first described function for the ROXYs in tree plants. Through this case study, we demonstrated the feasibility and efficacy of molecular technology applied to characterization of gene function in tree species.

Genome-wide characterization of NAC transcription factors in Camellia sinensis and the involvement of CsNAC28 in drought tolerance

The NAM, ATAF1/2, and CUC2 (NAC) transcription factors, which are members of a plant-specific gene family, play critical roles during the growth and development of plants and in their adaption to environmental stress. Few NAC transcription factors have been functionally characterized in tea plants (Camellia sinensis). Based on the analysis of the gene structure, motif pattern, and evolutionary relationship, we identified 104 NAC genes in C. sinensis. Among them, CsNAC28 is constitutively expressed in all organs, and most significantly, exhibiting remarkable responsiveness to abscisic acid (ABA) treatment and drought stress. ABA is a primary stress-related hormone. Recently, ABA-responsive element binding factor 2 (CsABF2) was identified in the ABA pathway of C. sinensis. However, the involvement of the CsABF2-mediated ABA pathway in regulating CsNACs was not known. Herein, a series of biochemical and genetic approaches supported the fact that CsNAC28 could potentially act as a transcription factor in the downstream of CsABF2. Furthermore, we investigated the function of CsNAC28 in the adapting of a plant to drought stress. The results showed that overexpression of CsNAC28 in Arabidopsis conferred hypersensitivity to ABA treatment and decreased the accumulation of reactive oxygen species (ROS), resulting in improved dehydration tolerance. Under conditions of drought, the expression levels of ABA pathway-related genes and drought stress‒inducible genes were greater in CsNAC28 overexpression lines than in the wild type. Our study's comprehensive characterization of NAC genes in C. sinensis could serve as a foundation for exploring the molecular mechanism of CsNAC-mediated drought responsiveness.