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Background Selenium (Se) deficiency causes a series of health disorders in humans, and Se concentrations in the edible parts of crops can be improved by altering exogenous Se species. However, the uptake, transport, subcellular distribution and metabolism of selenite, selenate and SeMet (selenomethionine) under the influence of phosphorus (P) has not been well characterized. Results The results showed that increasing the P application rate enhanced photosynthesis and then increased the dry matter weight of shoots with selenite and SeMet treatment, and an appropriate amount of P combined with selenite treatment increased the dry matter weight of roots by enhancing root growth. With selenite treatment, increasing the P application rate significantly decreased the concentration and accumulation of Se in roots and shoots. P1 decreased the Se migration coefficient, which could be attributed to the inhibited distribution of Se in the root cell wall, but increased distribution of Se in the root soluble fraction, as well as the promoted proportion of SeMet and MeSeCys (Se-methyl-selenocysteine) in roots. With selenate treatment, P0.1 and P1 significantly increased the Se concentration and distribution in shoots and the Se migration coefficient, which could be attributed to the enhanced proportion of Se (IV) in roots but decreased proportion of SeMet in roots. With SeMet treatment, increasing the P application rate significantly decreased the Se concentration in shoots and roots but increased the proportion of SeCys2 (selenocystine) in roots. Conclusion Compared with selenate or SeMet treatment, treatment with an appropriate amount of P combined with selenite could promote plant growth, reduce Se uptake, alter Se subcellular distribution and speciation, and affect Se bioavailability in wheat.

Desert-inhabiting cyanobacteria can tolerate extreme desiccation and quickly revive after rehydration. The regulatory mechanisms that enable their vegetative cells to resurrect upon rehydration are poorly understood. In this study, we identified a single gene family of high light-inducible proteins (Hlips) with dramatic expansion in the

As a common adverse environmental factor, heat stress (HS) not only drastically changes the plant transcriptome at the transcription level but also increases alternative splicing (AS), especially intron retention (IR) events. However, the exact mechanisms are not yet well understood. Here, we reported that NTC-related protein 1 (NTR1), which acts as an accessory component for spliceosome disassembly, is necessary for this process. The mutants of NTR1, both the T-DNA insertion and the point mutation identified through ethyl methanesulfonate (EMS) mutagenesis screening, are vulnerable to HS, indicating that NTR1 is essential for plant HS tolerance. At the molecular level, genes of response to heat and response to temperature stimulus are highly enriched among those of heat-induced but less-expressed ntr1 mutants. Moreover, a large portion of HS response (HSR) genes such as heat shock transcription factors (HSFs) and heat shock proteins (HSPs) are less induced by heat treatment, and more AS events, especially IR events, were found in heat-treated ntr1 mutants. Furthermore, HS suppressed the expression of NTR1 and NTR1-associated complex components. Thus, it is very likely that upon HS, the plant reduces the expression of the NTR1-associated complex to fulfill the fast demands for transcription of HSR genes such as HSFs and HSPs, which in turn results in the accumulation of improperly spliced especially IR products and eventually causes harm to plants.

Background Selenium (Se) deficiency caused a series of health disorders in human beings, and Se concentration in the edible parts of crops can be improved by altering exogenous Se species. However, the uptake, transport, subcellular distribution and metabolism of selenite, selenate and SeMet influenced by phosphorus (P) has not been well characterized. Results The resulted showed that increasing P supply enhanced photosynthesis and then increase the dry matter weight of shoots at selenite and SeMet, and appropriate P combined with selenite increased the dry matter weight of roots by enhancing root growth. At selenite, increasing P supply significantly decreased the concentration and accumulation of Se in roots and shoots. P1 decreased the Se migration coefficient, which could be attributed to the inhibited distribution of Se in root cell wall but increased distribution of Se in root soluble fraction, as well as the promoted proportion of SeMet and MeSeCys in roots. At selenate, P0.1 and P1 significantly increased the Se concentration and distribution in shoots and Se migration coefficient, which could be attributed to the enhanced proportion of Se(IV) in roots but decreased proportion of SeMet in roots. At SeMet, increasing P supply significantly decreased Se concentration in shoots and roots, but increased the proportion of SeCys in roots. Conclusion Compared with selenite or SeMet, appropriate P combined with selenite could promote plant growth, reduce Se uptake, alter Se subcellular distribution and speciation, and then affect the Se bioavailability in wheat.

Desert-inhabiting cyanobacteria can tolerate extreme desiccation and quickly revive after rehydration. The regulatory mechanisms that enable their vegetative cells to resurrect upon rehydration are poorly understood. In this study, we identified a single gene family of high light-inducible proteins (Hlips) with dramatic expansion in the Nostoc flagelliforme genome and found an intriguingly special convergence formed through four tandem gene duplication. The emerged four independent hlip genes form a gene cluster ( hlips-cluster ) and respond to dehydration positively. The gene mutants in N. flagelliforme were successfully generated by using gene-editing technology. Phenotypic analysis showed that the desiccation tolerance of hlips-cluster –deleted mutant decreased significantly due to impaired photosystem II repair, whereas heterologous expression of hlips-cluster from N. flagelliforme enhanced desiccation tolerance in Nostoc sp. PCC 7120. Furthermore, a transcription factor Hrf1 ( hlips-cluster repressor factor 1) was identified and shown to coordinately regulate the expression of hlips-cluster and desiccation-induced psbAs . Hrf1 acts as a negative regulator for the adaptation of N. flagelliforme to the harsh desert environment. Phylogenetic analysis revealed that most species in the Nostoc genus possess both tandemly repeated Hlips and Hrf1. Our results suggest convergent evolution of desiccation tolerance through the coevolution of tandem Hlips duplication and Hrf1 in subaerial Nostoc species, providing insights into the mechanism of desiccation tolerance in photosynthetic organisms.

Summary Plant stomata play a crucial role in leaf function, controlling water transpiration in response to environmental stresses and modulating the gas exchange necessary for photosynthesis. The phytohormone abscisic acid (ABA) promotes stomatal closure and inhibits light‐induced stomatal opening. The Arabidopsis thaliana E3 ubiquitin ligase COP1 functions in ABA‐mediated stomatal closure. However, the underlying molecular mechanisms are still not fully understood.Yeast two‐hybrid assays were used to identify ABA signaling components that interact with COP1, and biochemical, molecular and genetic studies were carried out to elucidate the regulatory role of COP1 in ABA signaling.The cop1 mutants are hyposensitive to ABA‐triggered stomatal closure under light and dark conditions. COP1 interacts with and ubiquitinates the Arabidopsis clade A type 2C phosphatases (PP2Cs) ABI/HAB group and AHG3, thus triggering their degradation. Abscisic acid enhances the COP1‐mediated degradation of these PP2Cs. Mutations in ABI1 and AHG3 partly rescue the cop1 stomatal phenotype and the phosphorylation level of OST1, a crucial SnRK2‐type kinase in ABA signaling.Our data indicate that COP1 is part of a novel signaling pathway promoting ABA‐mediated stomatal closure by regulating the stability of a subset of the Clade A PP2Cs. These findings provide novel insights into the interplay between ABA and the light signaling component in the modulation of stomatal movement.

In Arabidopsis, the plasma membrane transporter PUT3 is important to maintain the cellular homeostasis of polyamines and plays a role in stabilizing mRNAs of some heat-inducible genes. The plasma membrane Na+ /H+ transporter SOS1 and the protein kinase SOS2 are two salt-tolerance determinants crucial for maintaining intracellular Na+ and K+ homeostasis. Here, we report that PUT3 genetically and physically interacts with SOS1 and SOS2, and these interactions modulate PUT3 transport activity. Overexpression of PUT3 (PUT3OE) results in hypersensitivity of the transgenic plants to polyamine and paraquat. The hypersensitivity of PUT3OE is inhibited by the sos1 and sos2 mutations, which indicates that SOS1 and SOS2 are required for PUT3 transport activity. A protein interaction assay revealed that PUT3 physically interacts with SOS1 and SOS2 in yeast and plant cells. SOS2 phosphorylates PUT3 both in vitro and in vivo. SOS1 and SOS2 synergistically activate the polyamine transport activity of PUT3, and PUT3 also modulates SOS1 activity by activating SOS2 in yeast cells. Overall, our findings suggest that both plasma-membrane proteins PUT3 and SOS1 could form a complex with the protein kinase SOS2 in response to stress conditions and modulate the transport activity of each other through protein interactions and phosphorylation.

TPST is involved in fructose signaling to regulate the root development and expression of genes in biological processes including auxin biosynthesis and accumulation in Arabidopsis. Sulfonation of proteins by tyrosine protein sulfotransferases (TPST) has been implicated in many important biological processes in eukaryotic organisms. Arabidopsis possesses a single TPST gene and its role in auxin homeostasis and root development has been reported. Here we show that the Arabidopsis tpst mutants are hypersensitive to fructose. In contrast to sucrose and glucose, fructose represses primary root growth of various ecotypes of Arabidopsis at low concentrations. RNA-seq analysis identified 636 differentially expressed genes (DEGs) in Col-0 seedlings in response to fructose verses glucose. GO and KEGG analyses of the DEGs revealed that fructose down-regulates genes involved in photosynthesis, glucosinolate biosynthesis and IAA biosynthesis, but up-regulates genes involved in the degradation of branched amino acids, sucrose starvation response, and dark response. The fructose responsive DEGs in the tpst mutant largely overlapped with that in Col-0, and most DEGs in tpst displayed larger changes than in Col-0. Interestingly, the fructose up-regulated DEGs includes genes encoding two AtTPST substrate proteins, Phytosulfokine 2 (PSK2) and Root Meristem Growth Factor 7 (RGF7). Synthesized peptides of PSK-α and RGF7 could restore the fructose hypersensitivity of tpst mutant plants. Furthermore, auxin distribution and accumulation at the root tip were affected by fructose and the tpst mutation. Our findings suggest that fructose serves as a signal to regulate the expression of genes involved in various biological processes including auxin biosynthesis and accumulation, and that modulation of auxin accumulation and distribution in roots by fructose might be partly mediated by the TPST substrate genes PSK-α and RGF7.

Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth, productivity and quality. Plants have evolved mechanisms to perceive these environmental challenges, transmit the stress signals within cells as well as between cells and tissues, and make appropriate adjustments in their growth and development in order to survive and reproduce. In recent years, significant progress has been made on many fronts of the stress signaling research, particularly in understanding the downstream signaling events that culminate at the activation of stress- and nutrient limitation-responsive genes, cellular ion homeostasis, and growth adjustment. However, the revelation of the early events of stress signaling, particularly the identification of primary stress sensors, still lags behind. In this review, we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies.

Arsenic is a metalloid toxic to plants, animals and human beings. Small ubiquitin-like modifier (SUMO) conjugation is involved in many biological processes in plants. However, the role of SUMOylation in regulating plant arsenic response is still unclear. In this study, we found that dysfunction of SUMO E3 ligase SIZ1 improves arsenite resistance in Arabidopsis. Overexpression of the dominant-negative SUMO E2 variant resembled the arsenite-resistant phenotype of siz1 mutant, indicating that SUMOylation plays a negative role in plant arsenite detoxification. The siz1 mutant accumulated more glutathione (GSH) than the wild type under arsenite stress, and the arsenite-resistant phenotype of siz1 was depressed by inhibiting GSH biosynthesis. The transcript levels of the genes in the GSH biosynthetic pathway were increased in the siz1 mutant comparing with the wild type in response to arsenite treatment. Taken together, our findings revealed a novel function of SIZ1 in modulating plant arsenite response through regulating the GSH-dependent detoxification.

Lysine-ε-acetylation (Kac) is a post-translational modification (PTM) that is critical for metabolic regulation and cell signaling in mammals. However, its prevalence and importance in plants remain to be determined. Employing high-resolution tandem mass spectrometry, we analyzed protein lysine acetylation in five representative Arabidopsis organs with 2 ~ 3 biological replicates per organ. A total of 2887 Kac proteins and 5929 Kac sites were identified. This comprehensive catalog allows us to analyze proteome-wide features of lysine acetylation. We found that Kac proteins tend to be more uniformly expressed in different organs, and the acetylation status exhibits little correlation with the gene expression level, indicating that acetylation is unlikely caused by stochastic processes. Kac preferentially targets evolutionarily conserved proteins and lysine residues, but only a small percentage of Kac proteins are orthologous between rat and Arabidopsis. A large portion of Kac proteins overlap with proteins modified by other PTMs including ubiquitination, SUMOylation and phosphorylation. Although acetylation, ubiquitination and SUMOylation all modify lysine residues, our analyses show that they rarely target the same sites. In addition, we found that “reader” proteins for acetylation and phosphorylation, i.e., bromodomain-containing proteins and GRF (General Regulatory Factor)/14-3-3 proteins, are intensively modified by the two PTMs, suggesting that they are main crosstalk nodes between acetylation and phosphorylation signaling. Analyses of GRF6/14-3-3λ reveal that the Kac level of GRF6 is decreased under alkaline stress, suggesting that acetylation represses plant alkaline response. Indeed, K56ac of GRF6 inhibits its binding to and subsequent activation of the plasma membrane H+-ATPase AHA2, leading to hypersensitivity to alkaline stress. These results provide valuable resources for protein acetylation studies in plants and reveal that protein acetylation suppresses phosphorylation output by acetylating GRF/14-3-3 proteins.

Soil salinity severely hampers agricultural productivity. Under salt stress, excess Na+ accumulation causes cellular damage and plant growth retardation, and membrane Na+ transporters play central roles in Na+ uptake and exclusion to mitigate these adverse effects. In this study, we performed sos1 suppressor mutant (named sup) screening to uncover potential genetic interactors of SOS1 and additional salt tolerance mechanisms. Map-based cloning and sequencing identified a group of mutants harboring dominant gain-of-function mutations in the vacuolar Na+/H+ antiporter gene AtNHX1. The gain-of-function variants of AtNHX1 showed enhanced transporter activities in yeast cells and increased salt tolerance in Arabidopsis wild type plants. Ion content measurements indicated that at the cellular level, these gain-of-function mutations resulted in increased cellular Na+ accumulation likely due to enhanced vacuolar Na+ sequestration. However, the gain-of-function suppressor mutants showed reduced shoot Na+ but increased root Na+ accumulation under salt stress, indicating a role of AtNHX1 in limiting Na+ translocation from root to shoot. We also identified another group of sos1 suppressors with loss-of-function mutations in the Na+ transporter gene AtHKT1. Loss-of-function mutations in AtHKT1 and gain-of-function mutations in AtNHX1 additively suppressed sos1 salt sensitivity, which indicates that the three transporters, SOS1, AtNHX1 and AtHKT1 function independently but coordinately in controlling Na+ homeostasis and salt tolerance in Arabidopsis. Our findings provide valuable information about the target amino acids in NHX1 for gene editing to improve salt tolerance in crops.

Maintenance of cell wall integrity is of great importance not only for plant growth and development, but also for the adaptation of plants to adverse environments. However, how the cell wall integrity is modulated under salt stress is still poorly understood. Here, we report that a nuclear-localized Agenet domain-containing protein SWO1 (SWOLLEN 1) is required for the maintenance of cell wall integrity in Arabidopsis under salt stress. Mutation in SWO1 gene results in swollen root tips, disordered root cell morphology, and root elongation inhibition under salt stress. The swo1 mutant accumulates less cellulose and pectin but more lignin under high salinity. RNA-seq and ChIP-seq assays reveal that SWO1 binds to the promoter of several cell wall-related genes and regulates their expression under saline conditions. Further study indicates that SWO1 interacts with importin ɑ IMPA1 and IMPA2, which are required for the import of nuclear-localized proteins. The impa1 impa2 double mutant also exhibits root growth inhibition under salt stress and mutations of these two genes aggravate the salt-hypersensitive phenotype of the swo1 mutant. Taken together, our data suggest that SWO1 functions together with importin ɑ to regulate the expression of cell wall-related genes, which enables plants to maintain cell wall integrity under high salinity.

Maintaining the structural integrity of the photosynthetic apparatus during dehydration is critical for effective recovery of photosynthetic activity upon rehydration in a variety of desiccation-tolerant plants, but the underlying molecular mechanism is largely unclear. The subaerial cyanobacterium Nostoc flagelliforme can survive extreme dehydration conditions and quickly recovers its photosynthetic activity upon rehydration. In this study, we found that the expression of the molecular chaperone NfDnaK2 was substantially induced by dehydration, and NfDnaK2 proteins were primarily localized in the thylakoid membrane. NfDnaJ9 was identified to be the cochaperone partner of NfDnaK2, and their encoding genes shared similar transcriptional responses to dehydration. NfDnaJ9 interacted with the NfFtsH2 protease involved in the degradation of damaged D1 protein. Heterologous expression of NfdnaK2 enhanced PSII repair and drought tolerance in transgenic Nostoc sp. PCC 7120. Furthermore, the nitrate reduction (NarL)/nitrogen fixation (FixJ) family transcription factors response regulator (NfRre1) and photosynthetic electron transport-dependent regulator (NfPedR) were identified as putative positive regulators capable of binding to the promoter region of NfdnaK2 and they may mediate dehydration-induced expression of NfdnaK2 in N. flagelliforme Our findings provide novel insights into the molecular mechanism of desiccation tolerance in some xerotolerant microorganisms, which could facilitate future synthetic approaches to the creation of extremophiles in microorganisms and plants.

Nitrogen (N) is critical for zinc (Zn) uptake into plant roots, which promotes Zn accumulation and biofortification of grains in winter wheat (Triticum aestivum L.). However, little is known about the role of TaZIPs genes in the Zn uptake and translocation in response to N supply. This study explored a possible avenue to improve Zn uptake and translocation by adjusting N supply in winter wheat. Winter wheat (Triticum aestivum.cv Zhengmai379) was cultivated with low, medium and high N in a nutrition solution or a pot soil with or without Zn supply. Plants in hydroponic culture were harvested at 21 d after different treatments and those in the soil culture were harvested at grain filling stage, and N and Zn concentrations and accumulation, Zn translocation coefficient, and the expression of TaZIP3 and TaZIP7 in different tissues were determined. When N supply was increased, Zn concentration and accumulation in shoot, Zn accumulation in whole plants, and root-to-shoot translocation of Zn were decreased in the solution without Zn supply. In the solution with Zn supply, increasing N supply increased Zn concentration in shoot, and medium N supply increased Zn accumulation in shoot and whole plants. Increasing N supply increased Zn concentration and accumulation in root, stem, leaf, glume and grain, and Zn translocation form root to stem, but decreased Zn translocation from stem to leaf, stem to glume and glume to grain under both Zn-deficient and Zn-sufficient conditions. Medium N supply up-regulated the expression of TaZIP3 and TaZIP7 in the roots of winter wheat cultured under both Zn-deficient and Zn-sufficient conditions. In Zn-deficient soil, the expression of TaZIP3 and TaZIP7 in root and glume was up-regulated but that in stem and leaf was down-regulated by increasing N supply. Medium or high N supply induced the expression of TaZIP3 and TaZIP7 in different tissues of winter wheat grown under Zn-sufficient condition. Adequate N supply improves the grain Zn concentration through enhancing Zn uptake and root-to-shoot translocation, which could be mediated by induced expression of TaZIP3 and TaZIP7 in roots of winter wheat.

Exposure to short-term cold stress influences disease resistance by mechanisms that remain poorly characterized. The molecular basis of cold-activated immunity was therefore investigated in Arabidopsis thaliana inoculated with the bacterial pathogen Pst DC3000, using a transcriptomic analysis. Exposure to cold stress for 10 hr was sufficient to activate immunity, as well as H2 O2 accumulation and callose deposition. Transcriptome changes induced by the 10-hr cold treatment were similar to those caused by pathogen infection, including increased expression of the salicylic acid (SA) pathway marker genes, PR2 and PR5, and genes playing positive roles in defence against (hemi)-biotrophs. In contrast, transcripts encoding jasmonic acid (JA) pathway markers such as PR4 and MYC2 and transcripts with positive roles in defence against necrotrophs were less abundant following the 10-hr cold treatment. Cold-activated immunity was dependent on SA, being partially dependent on NPR1 and ICS1/SID2. In addition, transcripts encoding SA biosynthesis enzymes such as ICS2, PAL1, PAL2, and PAL4 (but not ICS1/SID2) and MES9 were more abundant, whereas GH3.5/WES1 and SOT12 transcripts that encode components involved in SA modification were less abundant following cold stress treatment. These findings show that cold stress cross-activates innate immune responses via a SA-dependent pathway.

Abscisic acid (ABA) signaling is critical for seed germination and abiotic stress responses in terrestrial plants. Pre-mRNA splicing is known to regulate ABA signaling. However, the involvement of canonical spliceosomal components in regulating ABA signaling is poorly understood. Here, we show that the spliceosome component Sm core protein SmEb plays an important role in ABA signaling. SmEb expression is up-regulated by ABA treatment, and analysis of Arabidopsis smeb mutant plants suggest that SmEb modulates the alternative splicing of the ABA signaling component HAB1 by enhancing the HAB1.1 splicing variant while repressing HAB1.2. Overexpression of HAB1.1 but not HAB1.2 rescues the ABA-hypersensitive phenotype of smeb mutants. Mutations in the transcription factor ABI3, 4, or 5 also reduce the ABA hypersensitivity of smeb mutants during seed germination. Our results show that the spliceosomal component SmEb plays an important role in ABA regulation of seed germination and early seedling development.

Mota Maradi is a sorghum line that exhibits holistic salinity tolerance mechanisms, making it a viable potential donor in breeding efforts for improved sorghum lines. High soil salinity is one of the global challenges for crop growth and productivity. Understanding the salinity tolerance mechanisms in crops is necessary for genetic breeding of salinity-tolerant crops. In this study, physiological and molecular mechanisms in sorghum were identified through a comparative analysis between a Nigerien salinity-tolerant sorghum landrace, Mota Maradi, and the reference sorghum line, BTx623. Significant differences on physiological performances were observed, particularly on growth and biomass gain, photosynthetic rate, and the accumulation of Na+, K+, proline, and sucrose. Transcriptome profiling of the leaves, leaf sheaths, stems, and roots revealed contrasting differentially expressed genes (DEGs) in Mota Maradi and BTx623 which supports the physiological observations from both lines. Among the DEGs, ion transporters such as HKT, NHX, AKT, HAK5, and KUP3 were likely responsible for the differences in Na+ and K+ accumulation. Meanwhile, DEGs involved in photosynthesis, cellular growth, signaling, and ROS scavenging were also identified between these two genotypes. Functional and pathway analysis of the DEGs has revealed that these processes work in concert and are crucial in elevated salinity tolerance in Mota Maradi. Our findings indicate how different complex processes work synergistically for salinity stress tolerance in sorghum. This study also highlights the unique adaptation of landraces toward their respective ecosystems, and their strong potential as genetic resources for future plant breeding endeavors.

Background Cadmium (Cd) accumulation in crops will affect the yield and quality of crops, and also harm human health. The application of selenium (Se) can reduce the absorption and transport of Cd in winter wheat. Results The result showed that increasing Se supply significantly decreased Cd concentration and accumulation in shoots and roots of winter wheat, and the root to shoot translocation of Cd. The Se supply increased the root length, surface area and root volume, but decreased the root average diameter. Increasing Se supply significantly decreased Cd concentration in cell wall, soluble fraction and cell organelle in roots and shoots. An increase of Se supply inhibited Cd distribution in the organelle of shoot and root, but enhanced Cd distribution in the soluble fraction of shoot and the cell wall of root. The Se supply also decreased the proportion of active Cd (ethanol-extractable (FE) Cd and deionized water-extractable (FW) Cd) in roots. In addition, the expression of TaNramp5-a, TaNramp5-b, TaHMA3-a, TaHMA3-b and TaHMA2 were significantly increased with the increase of Cd concentration in roots, and the expression of TaNramp5-a, TaNramp5-b and TaHMA2 in roots were down-regulated by increasing Se supply, regardless of Se supply or Cd stress, respectively. The expression of TaHMA3-b in root was significantly down-regulated by Se10 treatment at both Cd5 and Cd25 but up-regulated by Se5 treatment at Cd25. The expression of TaNramp5-a, TaNramp5-b, TaHMA3-a, TaHMA3-b and TaHMA2 in shoot were down-regulated by increasing Se supply at Cd5, and Se5 treatment up-regulated the expression of those genes in shoot at Cd25. Conclusions The results confirm that Se application limit Cd accumulation in wheat via regulating subcellular distribution and the chemical forms of Cd in tissues of winter wheat, as well as the expression of TaNramp5-a, TaNramp5-b and TaHMA2 in root.

© 2020 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Domestication has resulted in reduced salt tolerance in tomato. To identify the genetic components causing this deficiency, we performed a genome‐wide association study (GWAS) for root Na(+)/K(+) ratio in a population consisting of 369 tomato accessions with large natural variations. The most significant variations associated with root Na(+)/K(+) ratio were identified within the gene SlHAK20 encoding a member of the clade IV HAK/KUP/KT transporters. We further found that SlHAK20 transports Na(+) and K(+) and regulates Na(+) and K(+) homeostasis under salt stress conditions. A variation in the coding sequence of SlHAK20 was found to be the causative variant associated with Na(+)/K(+) ratio and confer salt tolerance in tomato. Knockout mutations in tomato SlHAK20 and the rice homologous genes resulted in hypersensitivity to salt stress. Together, our study uncovered a previously unknown molecular mechanism of salt tolerance responsible for the deficiency in salt tolerance in cultivated tomato varieties. Our findings provide critical information for molecular breeding to improve salt tolerance in tomato and other crops.

Terrestrial plants must cope with drought stress to survive. Under drought stress, plants accumulate the phytohormone abscisic acid (ABA) by increasing its biosynthesis and decreasing its catabolism. However, the regulatory pathways controlling ABA catabolism in response to drought remain largely unclear. Here, we report that the flowering repressor SHORT VEGETATIVE PHASE (SVP) is induced by drought stress and associates with the promoter regions of the ABA catabolism pathway genes CYP707A1, CYP707A3 and AtBG1, causing decreased expression of CYP707A1 and CYP707A3 but enhanced expression of AtBG1 in Arabidopsis leaves. Loss-of-function mutations in CYP707A1 and CYP707A3 or overexpression of AtBG1 could rescue the drought-hypersensitive phenotype of svp mutant plants by increasing cellular ABA levels. Collectively, our results suggest that SVP is a central regulator of ABA catabolism and that a regulatory pathway involving SVP, CYP707A1/3, and AtBG1 plays a critical role in plant response to water deficit and plant drought resistance.

MicroRNAs are 19- to 22-nucleotide small noncoding RNAs that have been implicated in abiotic stress responses. In this study, we found that knockdown of microRNA166, using the Short Tandem Target Mimic (STTM) system, resulted in morphological changes that confer drought resistance in rice (Oryza sativa). From a large-scale screen for miRNA knockdown lines in rice, we identified miR166 knockdown lines (STTM166); these plants exhibit a rolled-leaf phenotype, which is normally displayed by rice plants under drought stress. The leaves of STTM166 rice plants had smaller bulliform cells and abnormal sclerenchymatous cells, likely causing the rolled-leaf phenotype. The STTM166 plants had reduced stomatal conductance and showed decreased transpiration rates. The STTM166 lines also exhibited altered stem xylem and decreased hydraulic conductivity, likely due to the reduced diameter of the xylem vessels. Molecular analyses identified rice HOMEODOMAIN CONTAINING PROTEIN4 (OsHB4), a member of HD-Zip III gene family, as a major target of miR166; moreover, rice plants overexpressing a miR166-resistant form of OsHB4 resembled the STTM166 plants, including leaf rolling and higher drought resistance. The genes downstream of miR166-OsHB4 consisted of polysaccharide synthesis-related genes that may contribute to cell wall formation and vascular development. Our results suggest that drought resistance in rice can be increased by manipulating miRNAs, which leads to developmental changes, such as leaf rolling and reduced diameter of the xylem, that mimic plants’ natural responses to water-deficit stress.

Background Boehmeria nivea L. Gaud (Ramie) produces one of the longest natural fibers in nature. The bark of ramie mainly comprises of the phloem tissue of stem and is the raw material for fiber. Therefore, identifying the molecular regulation of phloem development is important for understanding of bast fiber biosynthesis and improvement of fiber quality in ramie. Results In this study, we collected top bud (TB), bark from internode elongating region (ER) and bark from internode fully elongated region (FER) from the ramie variety Zhongzhu No. 1. Histological study indicated that these samples contain phloem tissues at different developmental and maturation stages, with a higher degree of maturation of phloem tissue in FER. RNA sequencing (RNA-seq) was performed and de novo transcriptome was assembled. Unigenes and differentially expressed genes (DEGs) in these three samples were identified. The analysis of DEGs by using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed clear differences in gene expression between ER and FER. Some unigenes involved in secondary cell wall biosynthesis were up-regulated in both ER and FER, while unigenes for some cell wall components or cell wall modifications showed differential expression between ER and FER. In addition, the ethylene respond factors (ERFs) in the ethylene signaling pathway were up-regulated in FER, and ent-kaurenoic acid oxidase (KAO) and GA 20-oxidase (GA20ox) for gibberellins biosynthesis were up-regulated while GA 2-oxidase (GA2ox) for gibberellin inactivation was down-regulated in FER. Conclusions Both morphological study and gene expression analysis supported a burst of phloem and vascular developmental processes during the fiber maturation in the ramie stem, and ethylene and gibberellin are likely to be involved in this process. Our findings provide novel insights into the phloem development and fiber maturation in ramie, which could be useful for fiber improvement in ramie and other fiber crops.

Additional file 1: Table S1. FER had thicker fiber cell wall than ER. Table S2. Up-regulated DEGs in both ER and FER vs. TB involving in cell wall synthesis. Table S3. The most of up-regulated transcription factors in FER were ethylene responsive. Table S4. Ethylene active pathway up-regulated in FER comparing with ER. Table S5. KEGG enrichment top 20. Table S6. DEGs between ER and FER relative to Auxin. Table S7. DEGs between ER and FER involving in cell wall synthesis. Table S8. RT-qPCR verified unigenes.

Additional file 2: Figure S1. GO analysis of the DEGs between TB and ER. Figure S2. GO analysis of the DEGs between TB and FER. Figure S3. RT-qPCR detection of the selected DEGs among TB, ER and FER.

Additional file 1.

In Arabidopsis, the plasma membrane transporter PUT3 is important to maintain the cellular homeostasis of polyamines and plays a role in stabilizing mRNAs of some heat-inducible genes. The plasma membrane Na

Abiotic stresses greatly affect the immunity of plants. However, it is unknown whether pathogen infection affects abiotic stress tolerance of host plants. Here, the effect of defense response on cold and heat tolerance of host plants was investigated in Pst DC3000-infected Arabidopsis plants, and it was found that the pathogen-induced defense response could alleviate the injury caused by subsequent cold and heat stress (38°C). Transcriptomic sequencing plus RT-qPCR analyses showed that some abiotic stress genes are up-regulated in transcription by pathogen infection, including cold signaling components ICE1, CBF1, and CBF3, and some heat signaling components HSFs and HSPs. Moreover, the pathogen-induced alleviation of cold and heat injury was lost in NahG transgenic line (SA-deficient), sid2-2 and npr1-1 mutant plants, and pathogen-induced expression of cold and heat tolerance-related genes such as CBFs and HSPs, respectively, was lost or compromised in these plants, indicating that salicylic acid signaling pathway is required for the alleviation of cold and heat injury by pathogen infection. In short, our current work showed that in fighting against pathogens, host plants also enhance their cold and heat tolerance via a salicylic acid-dependent pathway.

Drought is one of the most deleterious environmental conditions affecting crop growth and productivity. Here we report the important roles of a nuclear-encoded chloroplast protein, PsbP Domain Protein 5 (PPD5), in drought resistance in Arabidopsis (Arabidopsis thaliana). From a forward genetic screen, a drought-resistant mutant named ppd5-2 was identified, which has a knockout mutation in PPD5. The ppd5 mutants showed increased H(2)O(2) accumulation in guard cells and enhanced stomatal closure in response to drought stress. Further analysis revealed that the chloroplast-localized PPD5 protein interacts with and is phosphorylated by OST1, and phosphorylation of PPD5 increases its protein stability. Double mutant ppd5-2ost1-3 exhibited phenotypes resembling the ost1-3 single mutant with decreased stomatal closure, increased water loss, reduced H(2)O(2) accumulation in guard cells, and hypersensitivity to drought stress. These results indicate that the chloroplast protein PPD5 negatively regulates drought resistance by modulating guard cell H(2)O(2) accumulation via an OST1-dependent pathway. Interestingly, the thf1-1 mutant defective in the chloroplast protein THF1 displayed drought-resistance and H(2)O(2) accumulation similar to the ppd5 mutants, but the thf1-1ost1-3 double mutant resembled the phenotypes of the thf1-1 single mutant. These results indicate that both OST1-dependent and OST1-independent pathways exist in the regulation of H(2)O(2) production in chloroplasts of guard cells under drought stress conditions. Additionally, our findings suggest a strategy to improve plant drought resistance through manipulation of chloroplast proteins.

Summary: Plants respond to cold stress by inducing the expression of transcription factors that regulate downstream genes to confer tolerance to freezing. We screened an Arabidopsis transfer DNA (T-DNA) insertion library and identified a cold-hypersensitive mutant, which we named stch4 (sensitive to chilling 4). STCH4/REIL2 encodes a ribosomal biogenesis factor that is upregulated upon cold stress. Overexpression of STCH4 confers chilling and freezing tolerance in Arabidopsis. The stch4 mutation reduces CBF protein levels and thus delayed the induction of C-repeat-binding factor (CBF) regulon genes. Ribosomal RNA processing is reduced in stch4 mutants, especially under cold stress. STCH4 associates with multiple ribosomal proteins, and these interactions are modulated by cold stress. These results suggest that the ribosome is a regulatory node for cold stress responses and that STCH4 promotes an altered ribosomal composition and functions in low temperatures to facilitate the translation of proteins important for plant growth and survival under cold stress. : Yu et al. show that the ribosomal biogenesis factor STCH4 confers cold stress tolerance in Arabidopsis by maintaining rRNA processing and promoting CBF protein translation. The ribosome is likely a site for cold stress response. Keywords: cold stress, rRNA processing, STCH4, protein translation, CBF, ribosome

Protein phosphatase 2A (PP2A) is an enzyme consisting of three subunits: a scaffolding A subunit, a regulatory B subunit, and a catalytic C subunit. PP2As were shown to play diverse roles in eukaryotes. In this study, the function of the Arabidopsis PP2A-C5 gene that encodes the catalytic subunit 5 of PP2A was studied using both loss-of-function and gain-of-function analyses. Loss-of-function mutant pp2a-c5-1 displayed more impaired growth during root and shoot development, whereas overexpression of PP2A-C5 conferred better root and shoot growth under different salt treatments, indicating that PP2A-C5 plays an important role in plant growth under salt conditions. Double knockout mutants of pp2a-c5-1 and salt overly sensitive (sos) mutants sos1-1, sos2-2, or sos3-1 showed additive sensitivity to NaCl, indicating that PP2A-C5 functions in a pathway different from the SOS signaling pathway. Using yeast two-hybrid analysis, four vacuolar membrane chloride channel (CLC) proteins, AtCLCa, AtCLCb, AtCLCc and AtCLCg, were found to interact with PP2A-C5. Moreover, overexpression of AtCLCc leads to increased salt tolerance and Cl- accumulation in transgenic Arabidopsis plants. These data indicate that PP2A-C5-mediated better growth under salt conditions might involve upregulation of CLC activities on vacuolar membranes and that PP2A-C5 could be used for improving salt tolerance in crops. This article is protected by copyright. All rights reserved.

Chloroplast as the site for photosynthesis is an essential organelle in plants, but little is known about its role in stomatal regulation and drought resistance. In this study, we show that two chloroplastic proteins essential for thylakoid formation negatively regulate drought resistance in Arabidopsis (Arabidopsis thaliana). By screening a mutant pool with T-DNA insertions in nuclear genes encoding chloroplastic proteins, we identified an HCF106 knockdown mutant exhibiting increased resistance to drought stress. The hcf106 mutant displayed elevated levels of reactive oxygen species (ROS) in guard cells, improved stomatal closure, and reduced water loss under drought conditions. The HCF106 protein was found to physically interact with THF1, a previously identified chloroplastic protein crucial for thylakoid formation. The thf1 mutant phenotypically resembled the hcf106 mutant and displayed more ROS accumulation in guard cells, increased stomatal closure, reduced water loss, and drought resistant phenotypes compared to the wild type. The hcf106thf1 double mutant behaved similarly as the thf1 single mutant. These results suggest that HCF106 and THF1 form a complex to modulate chloroplast function and that the complex is important for ROS production in guard cells and stomatal control in response to environmental stresses. Our results also suggest that modulating chloroplastic proteins could be a way for improving drought resistance in crops.

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme that has emerged as a central hub linking redox equilibrium and signal transduction in living organisms. The homeostasis of NAD is required for plant growth, development, and adaption to environmental cues. In this study, we isolated a chilling hypersensitive Arabidopsis thaliana mutant named qs-2 and identified the causal mutation in the gene encoding quinolinate synthase (QS) critical for NAD biosynthesis. The qs-2 mutant is also hypersensitive to salt stress and abscisic acid (ABA) but resistant to drought stress. The qs-2 mutant accumulates a reduced level of NAD and over-accumulates reactive oxygen species (ROS). The ABA-hypersensitivity of qs-2 can be rescued by supplementation of NAD precursors and by mutations in the ABA signaling components SnRK2s or RBOHF. Furthermore, ABA-induced over-accumulation of ROS in the qs-2 mutant is dependent on the SnRK2s and RBOHF. The expression of QS gene is repressed directly by ABI4, a transcription factor in the ABA response pathway. Together, our findings reveal an unexpected interplay between NAD biosynthesis and ABA and stress signaling, which is critical for our understanding of the regulation of plant growth and stress responses., Author summary Nicotinamide adenine dinucleotide (NAD) is a coenzyme essential for metabolisms and signal transduction in all living organisms, but little is known about its role in ABA-mediated plant growth inhibition. Here we show that a mutation in QS gene that causes reduced level of NAD influences the ABA signal transduction in Arabidopsis, suggesting a possible conserved role of NAD in abiotic stress response in plants. In Arabidopsis, disruption of NAD homeostasis leads to ROS burst that results in a growth inhibition during exogenous ABA treatment. The ROS-mediated reduction of plant growth is fully restored by the mutation in genes encoding SnRK2 kinases, which are the core components in ABA signal transduction. A feedback repression of the QS transcription requires ABI4, which is a well-known transcription factor in the downstream of ABA signaling. Our study reveals the importance of NAD in ROS burst and plant adaption to environmental cues, and also provides insights into the unexpected interplay between NAD homeostasis and ABA-mediated plant growth inhibition.

Soil salinization limits conventional agriculture since most food-based plant cultivars require low soil-sodium (Na+) levels for robust growth. Moreover, modern agricultural practices, especially in arid environments, can exacerbate soil salinization as belowground water sources utilized in irrigation are frequently tainted with salt. While salt tolerance has previously been shown to be augmented in several glycophyte species by the soil bacterium Bacillus subtilis (GB03), here we reported that this beneficial rhizobacterium promotes growth and augments higher salt-tolerance in halophyte grass Puccinellia tenuiflora. The optimal Bacillus subtilis strain for P. tenuiflora was screened. P. tenuiflora was grown from seeds with NaCl (0, 100, 200 and 300 mM) for salt treatments with or without inoculation of B. subtilis GB03. Growth parameters, chlorophyll content and endogenous Na+ and K+ contents were determined at the time of harvest. Seedlings were grown in medium with 0 or 200 mM NaCl, then were harvested to extract total RNA after 48 h of exposure to GB03 VOCs. Semi-quantitative RT-PCR was used to investigate the relative amount of PtHKT1;5, PtHKT2;1 and PtSOS1 in P. tenuiflora regulated by GB03. The optimal Bacillus subtilis strain for P. tenuiflora was GB03. GB03 significantly improved shoot and root growth at two, three, four and five weeks after inoculation. Under various salinity stresses, GB03 significantly promoted growth of P. tenuiflora seedlings. Na+ accumulation was reduced with K+ accumulation unaffected by GB03 exposure. Therefore, GB03 enhanced selective absorption capacity of P. tenuiflora for K+ over Na+ (SA) from media. Gene expression analysis demonstrated that GB03 up-regulated PtHKT1;5 and PtSOS1, but down-regulated PtHKT2;1 expression, specifically in roots when plants are grown under greatly-elevated salt conditions (200 mM NaCl). Our results presented here established that B. subtilis GB03 promoted the growth and improved the salt tolerance and the selective absorption capacity for K+ over Na+ in the monocotyledonous halophyte P. tenuiflora to a higher level. Interestingly, GB03-triggered up-regulation of PtHKT1;5 and PtSOS1 and down-regulation of PtHKT2;1 in roots reduced Na+ transport from root to shoot as well as Na+ uptake in roots. This study provides the physiological and molecular evidence that application of selected bacteria to salt-tolerant Monocots can ameliorate deleterious effects of high soil saline toxicity.

A novel Gram-stain-positive, motile, catalase- and oxidase-positive, endospore-forming, facultatively anaerobic rod, designated strain JSM 100118T, was isolated from an oyster (Crassostrea hongkongensis) collected from the tidal flat of Naozhou Island in the South China Sea. Strain JSM 100118T was able to grow with 0–13 % (w/v) NaCl (optimum 2–5 %), at pH 5.5–10.0 (optimum pH 7.5) and at 5–50 °C (optimum 30–35 °C). The cell-wall peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. The predominant respiratory quinone was menaquinone-7 and the major cellular fatty acids were anteiso-C15 : 0, iso-C15 : 0, C16 : 0 and C16 : 1ω11c. The polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, an unknown glycolipid and an unknown phospholipid. The genomic DNA G+C content was 35.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain JSM 100118T belonged to the genus Bacillus , and was most closely related to Bacillus litoralis SW-211T (98.9 % 16S rRNA gene sequence similarity), Bacillus halosaccharovorans E33T (98.3 %), Bacillus niabensis 4T19T (97.8 %) and Bacillus herbersteinensis D-1,5aT (97.1 %). The combination of results from the phylogenetic analysis, DNA–DNA hybridization, and phenotypic and chemotaxonomic characterization supported the conclusion that strain JSM 100118T represents a novel species of the genus Bacillus , for which the name Bacillus crassostreae sp. nov. is proposed. The type strain is JSM 100118T ( = CCTCC AB 2010452T = DSM 24486T = JCM 17523T).

Cytosolic sulphotransferases have been implicated in inactivation of endogenous steroid hormones and detoxification of xenobiotics in human and animals. Yet, the function of plant sulphotransferases in xenobiotic sulphonation and detoxification has not been reported. In this study, we show that the Arabidopsis sulphotransferase AtSOT12 could sulphonate the bacterial-produced toxin cycloheximide. Loss-of-function mutant sot12 exhibited hypersensitive phenotype to cycloheximide, and expression of AtSOT12 protein in yeast cells conferred resistance to this toxic compound. AtSOT12 exhibited broad specificity and could sulphonate a variety of xenobiotics including phenolic and polycyclic compounds. Enzyme kinetics analysis indicated that AtSOT12 has different selectivity for simple phenolics with different side chains, and the position of the side chain in the simple phenolic compounds affects substrate binding affinity and catalytic efficiency. We proposed that the broad specificity and induced production of AtSOT12 may have rendered this enzyme to not only modify endogenous molecules such as salicylic acid as we previously reported, but also sulphonate pathogen-produced toxic small molecules to protect them from infection. Sulphonation of small molecules in plants may constitute a rapid way to inactivate or change the physiochemical properties of biologically active molecules that could have profound effects on plant growth, development and defence.

Crop wild relatives harbor exotic and novel genetic resources, which hold great potential for crop improvement. Ipomoea imperati is a wild diploid relative of sweet potato with the capability of high salinity tolerance. We compared the transcriptomes of I. imperati under salt stress vs. control to identify candidate genes and pathways involved in salt response. De novo assembly produced 67,911 transcripts with a high depth of coverage. A total of 39,902 putative genes were assigned annotations, and 936 and 220 genes involved in salt response in roots and leaves, respectively. Functional analysis indicated a whole system response during salt stress in I. imperati, which included four metabolic processes: sensory initiation, transcriptional reprogramming, cellular protein component change, and cellular homeostasis regulation. We identified a number of candidate genes involved in the ABA signaling pathway, as well as transcription factors, transporters, antioxidant enzymes, and enzymes associated with metabolism of synthesis and catalysis. Furthermore, two membrane transporter genes, including vacuole cation/proton exchanger and inositol transporter, were considered to play important roles in salt tolerance. This study provided valuable information not only for understanding the genetic basis of ecological adaptation but also for future application in sweet potato and other crop improvements.

Polyamines (PAs) are polycationic compounds found in all living organisms and play crucial roles in growth and survival. We here show the 'Polyamine and paraquat (PQ) transport assay' protocol, which can be used to examine the uptake activity of PA/PQ transporters. We have used this protocol to demonstrate that PUT3 in Arabidopsis is a polyamine transporter and is able to take up spermidine and its analog paraquat.

The plant growth promoting rhizobacterium (PGPR) strain Bacillus amyloliquefaciens GB03, an important soil-borne bacterium, was shown to promote growth and abiotic stress tolerance in Arabidopsis thaliana as well as in some crop plants. This study aimed to evaluate the effects of GB03 on salt tolerance in Codonopsis pilosula, a traditional Chinese medicinal herb that is sensitive to salinity. Twenty-day-old seedlings of C. pilosula were either inoculated with GB03 or without it (as a control). At the same time, plants were treated with NaCl (0, 50, 100, or 150 mM) for 40 days. Growth parameters, photosynthetic indexes, malondialdehyde concentration, and leaf osmotic potential were measured after treatments. The result indicated that GB03 improved plant biomass of C. pilosula under salt conditions and improved the photosynthetic capacity by increasing net photosynthetic rate and stomatal conductance and decreasing intercellular CO2 concentration under both 0 and 50 mM NaCl. The bacterium strain also decreased leaf osmotic potential and peroxidation of membrane lipids that could help the plant adapt to saline environments. This study provides insights into the application of selected bacteria in the culture of important Chinese herbal plants under mild salinity.

Our previous work revealed that the soybean GmsSOS1 enhances salt tolerance in Arabidopsis. In this work, we studied the physiological mechanisms by which the GmsSOS1 confers salt and oxidative stress tolerance in Arabidopsis and yeast cells. Under salt stress condition, the GmsSOS1-expressing Arabidopsis plants displayed larger leaf area, lower leaf relative electrolytic leakage, less accumulation of H2O2, superoxide anion radicals (O2 −), and malondialdehyde compared with wild type. In consistent with these observations, the activities of antioxidant enzymes catalase, ascorbate peroxide, and peroxidase in the GmsSOS1-expressing plants were higher than those in wild type under salt stress. Combined salt and oxidative stresses caused more damage and higher accumulation of H2O2 and Na+ than single stress condition in both wild type and the GmsSOS1-expressing plants. However, the GmsSOS1-expressing Arabidopsis plants could maintain significantly lower levels of H2O2 and Na+ and exhibited better growth than wild type under either single or combined stress. The GmsSOS1 complemented the yeast plasma membrane-localized Na+/H+ antiporter and enhanced salt tolerance by reducing Na+ accumulation in yeast cells. Our results suggest that the soybean GmsSOS1 can alleviate the primary Na+ toxicity by limiting Na+ accumulation and mitigate the secondary oxidative stress through improving antioxidant enzyme activity.

Elevated sodium (Na+) decreases plant growth and, thereby, agricultural productivity. The ion transporter high-affinity K+ transporter (HKT)1 controls Na+ import in roots, yet dysfunction or overexpression of HKT1 fails to increase salt tolerance, raising questions as to HKT1's role in regulating Na+ homeostasis. Here, we report that tissue-specific regulation of HKT1 by the soil bacterium Bacillus subtilis GB03 confers salt tolerance in Arabidopsis thaliana. Under salt stress (100 mM NaCl), GB03 concurrently down- and upregulates HKT1 expression in roots and shoots, respectively, resulting in lower Na+ accumulation throughout the plant compared with controls. Consistent with HKT1 participation in GB03-induced salt tolerance, GB03 fails to rescue salt-stressed athkt1 mutants from stunted foliar growth and elevated total Na+ whereas salt-stressed Na+ export mutants sos3 show GB03-induced salt tolerance with enhanced shoot and root growth as well as reduced total Na+. These results demonstrate that tissue-specific regulation of HKT1 is critical for managing Na+ homeostasis in salt-stressed plants, as well as underscore the breadth and sophistication of plant–microbe interactions.

Histone modification in chromatin is one of the key control points in gene regulation in eukaryotic cells. Protein complexes composed of histone acetyltransferase or deacetylase, WD40 repeat protein, and many other components have been implicated in this process. Here, we report the identification and functional characterization of HOS15, a WD40-repeat protein crucial for repression of genes associated with abiotic stress tolerance through histone deacetylation in Arabidopsis . HOS15 shares high sequence similarity with human transducin-beta like protein (TBL), a component of a repressor protein complex involved in histone deacetylation. Mutation of the HOS15 gene renders mutant plants hypersensitive to freezing temperatures. HOS15 is localized in the nucleus and specifically interacts with histone H4. The level of acetylated histone H4 is higher in the hos15 mutant than in WT plants. Moreover, the stress inducible RD29A promoter is hyperinduced and associated with a substantially higher level of acetylated histone H4 in the hos15 mutant under cold stress conditions. Our results suggest a critical role for gene activation/repression by histone acetylation/deacetylation in plant acclimation and tolerance to cold stress.

Gleditsia sinensis is a Chinese native deciduous tree with a high economic and medicinal value. However, there is limited knowledge on the molecular processes responsible for the medical properties of this species owing to lack of bioinformatic resources such as available whole-genome sequences. In the present study, RNA sequencing data were used to analyze the transcriptome of G. sinensis, and a series of bioinformatic tools was used to explore the main genes involved in important molecular processes. A total of 75.57 million paired-end reads, with a length of 101 bp, were acquired from G. sinensis. Using the assembly tool Trinity, 233,751 transcripts were discovered. Among these, 85,795 were identified as unique transcripts and 59,326 unique transcripts were found to contain coding regions. Gene ontology analysis identified 27,637 unique transcripts that were clustered into 56 functional groups. Genes involved in flavonoid and terpenoid backbone biosynthesis and those encoding transcription factors were further analyzed. Sequence analysis revealed four putative G. sinensis chalcone isomerase genes (GsCHI) encoding the enzymes for flavonoid biosynthesis. GsCHI1 was found to be phylogenetically related to the chalcone isomerase of the family Leguminosae, and its transcript levels in different tissues were higher than those of GsCHI2, GsCHI3, and GsCHI4. Furthermore, 15,014 simple sequence repeat (SSR) markers were discovered in the transcript library, and 5170 primers were generated for the SSR loci. The genetic and genomic information presented in this study will be helpful for future studies on gene discovery and molecular processes in G. sinensis.

*Summary Salt Overly Sensitive 1 (SOS1), a plasma membrane Na+ /H + antiporter in Arabidopsis, is a salt tolerance determinant crucial for the maintenance of ion homeostasis in saline stress conditions. SOS1 mRNA is unstable at normal growth conditions, but its stability is substantially increased under salt stress and other ionic and dehydration stresses. In addition, H 2O2 treatment increases the stability of SOS1 mRNA. SOS1 mRNA is inherently unstable and rapidly degraded with a half-life of approximately 10 min. Rapid decay of SOS1 mRNA requires new protein synthesis. Stress-induced SOS1 mRNA stability is mediated by reactive oxygen species (ROS). NADPH oxidase is also involved in the upregulation of SOS1 mRNA stability, presumably through the control of extracellular ROS production. The cis-element required for SOS1 mRNA instability resides in the 500-bp region within the 2.2 kb at the 3¢ end of the SOS1 mRNA. Furthermore, mutations in the SOS1 gene render sos1 mutants more tolerant to paraquat, a non-selective herbicide causing oxidative stress, indicating that SOS1 plays negative roles in tolerance of oxidative stress. A hypothetical model for the signaling pathway involving SOS1-mediated pH changes, NADPH oxidase activation, apoplastic ROS production and downstream signaling transduction is proposed, and the biological significance of ROS-mediated induction of SOS1 mRNA stability is discussed.

To identify salt tolerance determinants, we screened for double mutants from a T-DNA tagged sos3-1 mutant population in the Arabidopsis Col-0 gl1 background. The shs1-1 (sodium hypersensitive) sos3-1 mutant was isolated as more sensitive to NaCl than sos3-1 plants. TAIL-PCR revealed that the introduced T-DNA was located 62 bp upstream of the initiation codon of an adenylate translocator-like protein gene on chromosome IV. SHS1 mRNA did not accumulate in shs1-1 sos3-1 plants although it accumulated in shoots of both sos3-1 and the wild type plants, indicating that this gene is inactive in the mutant. Genetic co-linkage analysis revealed that the mutation causing the phenotype segregated as a recessive, single gene mutation. This mutant showed altered sensitive responses to salt as well as to cold stress. It also demonstrated sugar sensitive and ABA insensitive phenotypes including enhanced germination, reduced growth, altered leaf morphology, and necrosis on leaves at an early growth stage. Sensitivity of sos3-1 shs1-1 root growth to LiCl, KCl, and mannitol was not significantly different from growth of sos3-1 roots. Further, expression of 35S::SHS1 in sos3-1 shs1-1 plants complemented NaCl and sugar sensitivity and partially restored the leaf morphology.

The myristoylated calcium sensor SOS3 and its interacting protein kinase, SOS2, play critical regulatory roles in salt tolerance. Mutations in either of these proteins render Arabidopsis thaliana plants hypersensitive to salt stress. We report here the isolation and characterization of a mutant called enh1-1 that enhances the salt sensitivity of sos3-1 and also causes increased salt sensitivity by itself. ENH1 encodes a chloroplast-localized protein with a PDZ domain at the N-terminal region and a rubredoxin domain in the C-terminal part. Rubredoxins are known to be involved in the reduction of superoxide in some anaerobic bacteria. The enh1-1 mutation causes enhanced accumulation of reactive oxygen species (ROS), particularly under salt stress. ROS also accumulate to higher levels in sos2-1 but not in sos3-1 mutants. The enh1-1 mutation does not enhance sos2-1 phenotypes. Also, enh1-1 and sos2-1 mutants, but not sos3-1 mutants, show increased sensitivity to oxidative stress. These results indicate that ENH1 functions in the detoxification of reactive oxygen species resulting from salt stress by participating in a new salt tolerance pathway that may involve SOS2 but not SOS3.