Identification of an apoplastic protein involved in the initial phase of salt stress response in rice root by two-dimensional electrophoresis

ZmABF4-ZmVIL2/ZmFIP37 module enhances drought tolerance in maize seedlings

Drought, as a primary environmental factor, imposes significant constraints on developmental processes and productivity of plants. PHDs were identified as stress-responsive genes in a wide range of eukaryotes. However, the regulatory mechanisms governing PHD genes in maize under abiotic stress conditions are still largely unknown and require further investigation. Here, we identified a mutant, zmvil2, in the EMS mutant library with a C to T mutation in the exon of the Zm00001d053875 (VIN3-like protein 2, ZmVIL2), resulting in premature termination of protein coding. ZmVIL2 belongs to PHD protein family. Compared to WT, zmvil2 mutant exhibited increased sensitivity to drought stress. Consistently, overexpression of ZmVIL2 enhances drought resistance in maize. Y2H, BiFC, and Co-IP experiments revealed that ZmVIL2 directly interacts with ZmFIP37 (FKBP12-interacting protein of 37). zmfip37 knockout mutants also exhibit decreased drought tolerance. Interestingly, we demonstrated that ZmABF4 directly binds to the ZmVIL2 promoter to enhance its activity in yeast one hybrid (Y1H), electrophoretic mobility shift assay (EMSA) and dual luciferase reporter assays. Therefore, we uncovered a novel model ZmABF4-ZmVIL2/ZmFIP37 that promotes drought tolerance in maize. Overall, these findings have enriched the knowledge of the functions of PHD genes in maize and provides genetic resources for breeding stress-tolerant maize varieties.

Response of seed germination, seedling growth and physiological characteristics to alkali stress in halophyte Suaeda liaotungensis

Soil salinization has been considered as a major environmental threat to plant growth. Different types of salt in saline soil have different effects on germination and seedling growth. Effect of NaCl on germination and seedling establishment in Suaeda liaotungensis have been reported, but its response to alkali stress remains unclear. Our results showed that brown seeds had higher germination rate, however, black seeds had higher germination recovery percentage under alkali stress. Na2CO3 had stronger inhibitory effect on germination and seedling growth than NaHCO3. As the concentration of alkali stress increased, the ROS level of brown seeds gradually ascended, while that of black seeds decreased first and then ascended. MDA content of dimorphic seeds significantly increased under alkali stress. The trend of SOD, POD and CAT activity between dimorphic seeds was similar under the same type of alkali stress. Alkali stress enhanced proline content of dimorphic seeds, and dimorphic seeds in NaHCO3 solution had higher proline content than Na2CO3 solution. Moreover, radicle and shoot tolerance indexes of seedlings in NaHCO3 solution were significantly higher than that of Na2CO3 solution. Under strong alkali stress, seedlings in NaHCO3 solution had significantly lower ROS level and MDA content as well as higher antioxidant enzyme activity than Na2CO3 solution. This study comprehensively compared the morphological and physiological characteristics in germination and seedlings to better reveal the saline-alkali tolerance mechanisms in S. liaotungensis.

Evolutionary assembly of the plant terrestrialization toolkit from protein domains

Land plants (embryophytes) came about in a momentous evolutionary singularity: plant terrestrialization. This event marks not only the conquest of land by plants but also the massive radiation of embryophytes into a diverse array of novel forms and functions. The unique suite of traits present in the earliest land plants is thought to have been ushered in by a burst in genomic novelty. Here, we asked the question of how these bursts were possible. For this, we explored: (i) the initial emergence and (ii) the reshuffling of domains to give rise to hallmark environmental response genes of land plants. We pinpoint that a quarter of the embryophytic genes for stress physiology are specific to the lineage, yet a significant portion of this novelty arises not de novo but from reshuffling and recombining of pre-existing domains. Our data suggest that novel combinations of old genomic substrate shaped the plant terrestrialization toolkit, including hallmark processes in signalling, biotic interactions and specialized metabolism.

CsHSFA1d Promotes Drought Stress Tolerance by Increasing the Content of Raffinose Family Oligosaccharides and Scavenging Accumulated Reactive Oxygen Species in Cucumber

Drought is the most severe form of stress experienced by plants worldwide. Cucumber is a vegetable crop that requires a large amount of water throughout the growth period. In our previous study, we identified that overexpression of CsHSFA1d could improve cold tolerance and the content of endogenous jasmonic acid in cucumber seedlings. To explore the functional diversities of CsHSFA1d, we treat the transgenic plants under drought conditions. In this study, we found that the heat shock transcription factor HSFA1d (CsHSFA1d) could improve drought stress tolerance in cucumber. CsHSFA1d overexpression increased the expression levels of galactinol synthase (CsGolS3) and raffinose synthase (CsRS) genes, encoding the key enzymes for raffinose family oligosaccharide (RFO) biosynthesis. Furthermore, the lines overexpressing CsHSFA1d showed higher enzymatic activity of GolS and raffinose synthase to increase the content of RFO. Moreover, the CsHSFA1d-overexpression lines showed lower reactive oxygen species (ROS) accumulation and higher ROS-scavenging enzyme activity after drought treatment. The expressions of antioxidant genes CsPOD2, CsAPX1 and CsSOD1 were also upregulated in CsHSFA1d-overexpression lines. The expression levels of stress-responsive genes such as CsRD29A, CsLEA3 and CsP5CS1 were increased in CsHSFA1d-overexpression lines after drought treatment. We conclude that CsHSFA1d directly targets and regulates the expression of CsGolS3 and CsRS to promote the enzymatic activity and accumulation of RFO to increase the tolerance to drought stress. CsHSFA1d also improves ROS-scavenging enzyme activity and gene expression indirectly to reduce drought-induced ROS overaccumulation. This study therefore offers a new gene target to improve drought stress tolerance in cucumber and revealed the underlying mechanism by which CsHSFA1d functions in the drought stress by increasing the content of RFOs and scavenging the excessive accumulation of ROS.

SOS1 tonoplast neo-localization and the RGG protein SALTY are important in the extreme salinity tolerance of Salicornia bigelovii

The identification of genes involved in salinity tolerance has primarily focused on model plants and crops. However, plants naturally adapted to highly saline environments offer valuable insights into tolerance to extreme salinity. Salicornia plants grow in coastal salt marshes, stimulated by NaCl. To understand this tolerance, we generated genome sequences of two Salicornia species and analyzed the transcriptomic and proteomic responses of Salicornia bigelovii to NaCl. Subcellular membrane proteomes reveal that SbiSOS1, a homolog of the well-known SALT-OVERLY-SENSITIVE 1 (SOS1) protein, appears to localize to the tonoplast, consistent with subcellular localization assays in tobacco. This neo-localized protein can pump Na+ into the vacuole, preventing toxicity in the cytosol. We further identify 11 proteins of interest, of which SbiSALTY, substantially improves yeast growth on saline media. Structural characterization using NMR identified it as an intrinsically disordered protein, localizing to the endoplasmic reticulum in planta, where it can interact with ribosomes and RNA, stabilizing or protecting them during salt stress.

Overexpression of the WRKY transcription factor gene NtWRKY65 enhances salt tolerance in tobacco (Nicotiana tabacum)

BACKGROUND

Salt stress severely inhibits plant growth, and the WRKY family transcription factors play important roles in salt stress resistance. In this study, we aimed to characterize the role of tobacco (Nicotiana tabacum) NtWRKY65 transcription factor gene in salinity tolerance.

RESULTS

This study characterized the role of tobacco (Nicotiana tabacum) NtWRKY65 transcription factor gene in salinity tolerance using four NtWRKY65 overexpression lines. NtWRKY65 is localized to the nucleus, has transactivation activity, and is upregulated by NaCl treatment. Salinity treatment resulted in the overexpressing transgenic tobacco lines generating significantly longer roots, with larger leaf area, higher fresh weight, and greater chlorophyll content than those of wild type (WT) plants. Moreover, the overexpressing lines showed elevated antioxidant enzyme activity, reduced malondialdehyde content, and leaf electrolyte leakage. In addition, the Na+ content significantly decreased, and the K+/Na+ ratio was increased in the NtWRKY65 overexpression lines compared to those in the WT. These results suggest that NtWRKY65 overexpression enhances salinity tolerance in transgenic plants. RNA-Seq analysis of the NtWRKY65 overexpressing and WT plants revealed that NtWRKY65 might regulate the expression of genes involved in the salt stress response, including cell wall component metabolism, osmotic stress response, cellular oxidant detoxification, protein phosphorylation, and the auxin signaling pathway. These results were consistent with the morphological and physiological data. These findings indicate that NtWRKY65 overexpression confers enhanced salinity tolerance.

CONCLUSIONS

Our results indicated that NtWRKY65 is a critical regulator of salinity tolerance in tobacco plants.

Cocoa Apoplastome Contains Defense Proteins Against Pathogens

The apoplast performs important functions in the plant, such as defense against stress, and compounds present form the apoplastic washing fluid (AWF). The fungus Moniliophthora perniciosa, the causal agent of witches' broom disease (WBD) in Theobroma cacao, initially colonizes the apoplast in its biotrophic phase. In this period, the fungus can remain for approximately 60 days, until it changes to its second phase, causing tissue death and consequently large loss in the production of beans. To better understand the importance of the apoplast in the T. cacao-M. perniciosa interaction, we performed the first apoplastic proteomic mapping of two contrasting genotypes for WBD resistance (CCN51-resistant and Catongo-susceptible). Based on two-dimensional gel analysis, we identified 36 proteins in CCN-51 and 15 in Catongo. We highlight PR-proteins, such as peroxidases, β-1,3-glucanases, and chitinases. A possible candidate for a resistance marker of the CCN-51 genotype, osmotin, was identified. The antioxidative metabolism of the superoxide dismutase (SOD) enzyme showed a significant increase (P < 0.05) in the AWF of the two genotypes under field conditions (FD). T. cacao AWF inhibited the germination of M. perniciosa basidiospores (>80%), in addition to causing morphological changes. Our results shed more light on the nature of the plant's defense performed by the apoplast in the T. cacao-M. perniciosa interaction in the initial (biotrophic) phase of fungal infection and therefore make it possible to expand WBD control strategies based on the identification of potential targets for resistance markers and advance scientific knowledge of the disease.

An update on evolutionary, structural, and functional studies of receptor-like kinases in plants

All living organisms must develop mechanisms to cope with and adapt to new environments. The transition of plants from aquatic to terrestrial environment provided new opportunities for them to exploit additional resources but made them vulnerable to harsh and ever-changing conditions. As such, the transmembrane receptor-like kinases (RLKs) have been extensively duplicated and expanded in land plants, increasing the number of RLKs in the advanced angiosperms, thus becoming one of the largest protein families in eukaryotes. The basic structure of the RLKs consists of a variable extracellular domain (ECD), a transmembrane domain (TM), and a conserved kinase domain (KD). Their variable ECDs can perceive various kinds of ligands that activate the conserved KD through a series of auto- and trans-phosphorylation events, allowing the KDs to keep the conserved kinase activities as a molecular switch that stabilizes their intracellular signaling cascades, possibly maintaining cellular homeostasis as their advantages in different environmental conditions. The RLK signaling mechanisms may require a coreceptor and other interactors, which ultimately leads to the control of various functions of growth and development, fertilization, and immunity. Therefore, the identification of new signaling mechanisms might offer a unique insight into the regulatory mechanism of RLKs in plant development and adaptations. Here, we give an overview update of recent advances in RLKs and their signaling mechanisms.

A novel R2R3-MYB transcription factor PbMYB1L of Pyrus bretschneideri regulates cold tolerance and anthocyanin accumulation

KEY MESSAGE

PbMYB1L enhances the cold tolerance and anthocyanin accumulation of transgenic Arabidopsis by regulating the expression of genes related to the cold-responsive genes pathway and anthocyanin synthesis pathway. MYB transcription factors (TFs) have been demonstrated to play diverse roles in plant growth and development. In the present study, we identified a novel R2R3-MYB transcription factor, PbMYB1L, from the peel of 'Red Zaosu' pear (Pyrus bretschneideri), which was induced by cold stress and acted as a positive regulator in anthocyanin biosynthesis. Notably, the transgenic Arabidopsis lines exhibited enhanced tolerance to cold stress. Compared to the Arabidopsis wild-type plants, the transgenic lines displayed longer primary roots and reduced reactive oxygen species (ROS) levels including O2-, hydrogen peroxide (H2O2), and malondialdehyde (MDA). Furthermore, significant upregulation of key cold-responsive genes AtCBF1, AtCBF2, AtCBF3, AtCBF4, and AtKIN1 was observed in the transgenic plants under cold stress conditions compared to wild type. Arabidopsis plants overexpressing PbMYB1L had significant anthocyanin accumulation in leaves after cold treatment with quantitative results indicating higher expression of anthocyanin structural genes compared to wild type. These findings suggest that PbMYB1L not only plays a vital role in conferring cold tolerance but also acts as a crucial regulator of anthocyanin biosynthesis.

Molecular mechanism analysis of ZmRL6 positively regulating drought stress tolerance in maize

MYB-related genes, a subclass of MYB transcription factor family, have been documented to play important roles in biological processes such as secondary metabolism and stress responses that affect plant growth and development. However, the regulatory roles of MYB-related genes in drought stress response remain unclear in maize. In this study, we discovered that a 1R-MYB gene, ZmRL6, encodes a 96-amino acid protein and is highly drought-inducible. We also found that it is conserved in both barley (Hordeum vulgare L.) and Aegilops tauschii. Furthermore, we observed that overexpression of ZmRL6 can enhance drought tolerance while knock-out of ZmRL6 by CRISPR-Cas9 results in drought hypersensitivity. DAP-seq analyses additionally revealed the ZmRL6 target genes mainly contain ACCGTT, TTACCAAAC and AGCCCGAG motifs in their promoters. By combining RNA-seq and DAP-seq results together, we subsequently identified eight novel target genes of ZmRL6 that are involved in maize's hormone signal transduction, sugar metabolism, lignin synthesis, and redox signaling/oxidative stress. Collectively, our data provided insights into the roles of ZmRL6 in maize's drought response.

Emerging Roles of Receptor-like Protein Kinases in Plant Response to Abiotic Stresses

The productivity of plants is hindered by unfavorable conditions. To perceive stress signals and to transduce these signals to intracellular responses, plants rely on membrane-bound receptor-like kinases (RLKs). These play a pivotal role in signaling events governing growth, reproduction, hormone perception, and defense responses against biotic stresses; however, their involvement in abiotic stress responses is poorly documented. Plant RLKs harbor an N-terminal extracellular domain, a transmembrane domain, and a C-terminal intracellular kinase domain. The ectodomains of these RLKs are quite diverse, aiding their responses to various stimuli. We summarize here the sub-classes of RLKs based on their domain structure and discuss the available information on their specific role in abiotic stress adaptation. Furthermore, the current state of knowledge on RLKs and their significance in abiotic stress responses is highlighted in this review, shedding light on their role in influencing plant-environment interactions and opening up possibilities for novel approaches to engineer stress-tolerant crop varieties.

Integrated Analysis of the Transcriptome and Metabolome of Brassica rapa Revealed Regulatory Mechanism under Heat Stress

Affected by global warming; heat stress is the main limiting factor for crop growth and development. Brassica rapa prefers cool weather, and heat stress has a significant negative impact on its growth, development, and metabolism. Understanding the regulatory patterns of heat-resistant and heat-sensitive varieties under heat stress can help deepen understanding of plant heat tolerance mechanisms. In this study, an integrative analysis of transcriptome and metabolome was performed on the heat-tolerant ('WYM') and heat-sensitive ('AJH') lines of Brassica rapa to reveal the regulatory networks correlated to heat tolerance and to identify key regulatory genes. Heat stress was applied to two Brassica rapa cultivars, and the leaves were analyzed at the transcriptional and metabolic levels. The results suggest that the heat shock protein (HSP) family, plant hormone transduction, chlorophyll degradation, photosynthetic pathway, and reactive oxygen species (ROS) metabolism play an outstanding role in the adaptation mechanism of plant heat tolerance. Our discovery lays the foundation for future breeding of horticultural crops for heat resistance.

Differences in Physiological Characteristics, Seed Germination, and Seedling Establishment in Response to Salt Stress between Dimorphic Seeds in the Halophyte Suaeda liaotungensis

Soil salinization is an increasing agricultural problem around the world, affecting crop productivity and quality. Seed germination and seedling establishment are susceptible to salt stress. Suaeda liaotungensis is a halophyte with strong salt tolerance that produces dimorphic seeds to adapt to the saline environment. Differences in physiological characteristics, seed germination, and seedling establishment in response to salt stress between dimorphic seeds in S. liaotungensis have not been reported. The results showed that brown seeds had significantly higher H₂O₂ and O₂^-. levels and betaine content, as well as POD and CAT activities, while they had significantly lower MDA and proline contents and SOD activity than black seeds. Light promoted the germination of brown seeds in a certain temperature range, and brown seeds could reach a higher germination percentage in a wide temperature range. However, light and temperature had no effect on the germination percentage of black seeds. Brown seeds had higher germination than black seeds under the same NaCl concentration. The final germination of brown seeds was significantly decreased as salt concentration increased, whereas this had no effect on the final germination of black seeds. POD and CAT activities, as well as MDA content, in brown seeds were significantly higher than those in black seeds during germination under salt stress. Additionally, the seedlings from brown seeds were more tolerant to salinity than those from black seeds. Therefore, these results will give an in-depth understanding of the adaptation strategies of dimorphic seeds to a salinization environment, and better exploitation and utilization of S. liaotungensis.

An activated form of NB-ARC protein RLS1 functions with cysteine-rich receptor-like protein RMC to trigger cell death in rice

A key event that follows pathogen recognition by a resistance (R) protein containing an NB-ARC (nucleotide-binding adaptor shared by Apaf-1, R proteins, and Ced-4) domain is hypersensitive response (HR)-type cell death accompanied by accumulation of reactive oxygen species and nitric oxide. However, the integral mechanisms that underlie this process remain relatively opaque. Here, we show that a gain-of-function mutation in the NB-ARC protein RLS1 (Rapid Leaf Senescence 1) triggers high-light-dependent HR-like cell death in rice. The RLS1-mediated defense response is largely independent of salicylic acid accumulation, NPR1 (Nonexpressor of Pathogenesis-Related Gene 1) activity, and RAR1 (Required for Mla12 Resistance 1) function. A screen for suppressors of RLS1 activation identified RMC (Root Meander Curling) as essential for the RLS1-activated defense response. RMC encodes a cysteine-rich receptor-like secreted protein (CRRSP) and functions as an RLS1-binding partner. Intriguingly, their co-expression resulted in a change in the pattern of subcellular localization and was sufficient to trigger cell death accompanied by a decrease in the activity of the antioxidant enzyme APX1. Collectively, our findings reveal an NB-ARC-CRRSP signaling module that modulates oxidative state, the cell death process, and associated immunity responses in rice.

High-throughput identification of novel heat tolerance genes via genome-wide pooled mutant screens in the model green alga Chlamydomonas reinhardtii

Different high temperatures adversely affect crop and algal yields with various responses in photosynthetic cells. The list of genes required for thermotolerance remains elusive. Additionally, it is unclear how carbon source availability affects heat responses in plants and algae. We utilized the insertional, indexed, genome-saturating mutant library of the unicellular, eukaryotic green alga Chlamydomonas reinhardtii to perform genome-wide, quantitative, pooled screens under moderate (35°C) or acute (40°C) high temperatures with or without organic carbon sources. We identified heat-sensitive mutants based on quantitative growth rates and identified putative heat tolerance genes (HTGs). By triangulating HTGs with heat-induced transcripts or proteins in wildtype cultures and MapMan functional annotations, we presented a high/medium-confidence list of 933 Chlamydomonas genes with putative roles in heat tolerance. Triangulated HTGs include those with known thermotolerance roles and novel genes with little or no functional annotation. About 50% of these high-confidence HTGs in Chlamydomonas have orthologs in green lineage organisms, including crop species. Arabidopsis thaliana mutants deficient in the ortholog of a high-confidence Chlamydomonas HTG were also heat sensitive. This work expands our knowledge of heat responses in photosynthetic cells and provides engineering targets to improve thermotolerance in algae and crops.

A Proteomics Insight into Advancements in the Rice-Microbe Interaction

Rice is one of the most-consumed foods worldwide. However, the productivity and quality of rice grains are severely constrained by pathogenic microbes. Over the last few decades, proteomics tools have been applied to investigate the protein level changes during rice-microbe interactions, leading to the identification of several proteins involved in disease resistance. Plants have developed a multi-layered immune system to suppress the invasion and infection of pathogens. Therefore, targeting the proteins and pathways associated with the host's innate immune response is an efficient strategy for developing stress-resistant crops. In this review, we discuss the progress made thus far with respect to rice-microbe interactions from side views of the proteome. Genetic evidence associated with pathogen-resistance-related proteins is also presented, and challenges and future perspectives are highlighted in order to understand the complexity of rice-microbe interactions and to develop disease-resistant crops in the future.

Cold acclimation alleviates cold stress-induced PSII inhibition and oxidative damage in tobacco leaves

This study aimed to explore how cold acclimation (CA) modulates cold stress in tobacco leaves and reveal the relationship between CA and cold stress resistance, and the mechanism of CA-induced plant resistance to cold stress. This study examined the effects of CA treatment (at 8-10℃ for 2 d) on the cold tolerance of tobacco leaves under 4°C cold stress treatment using seedlings without CA treatment as the control (NA). In both CA and NA leaves, cold stress treatment resulted in a decrease in maximum photochemical efficiency of PSII (Fv/Fm), increase in relative variable fluorescence (VJ) at 2 ms on the standardized OJIP curve, inhibition of PSII activity, and impairment of electron transfer on the acceptor side. Besides increasing the malondialdehyde (MDA) content and electrolyte leakage rate, the cold stress exacerbated the degree of membrane peroxidation. The CA treatment also induced the accumulation of reactive oxygen species (ROS), including superoxide anion (O2·-) and H2O2, and increased the activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbic acid peroxidase (APX). The CA treatment also enhanced the accumulation of soluble sugar (SS) and soluble protein (SP), cyclic electron flow (CEF), and the proportion of regulatory energy dissipation Y(NPQ). Moreover, CA+ cold stress treatment significantly reduced CEF and Y(NPQ) in tobacco leaves than under NA+ cold stress treatment, thus significantly alleviating the degree of PSII photoinhibition. In conclusion, CA treatment significantly alleviated PSII photoinhibition and oxidative damage in tobacco leaves under cold stress treatment. Improvement in cold resistance of tobacco leaves is associated with the induction of antioxidant enzyme activity, accumulation of osmoregulation substances, and initiation of photoprotective mechanisms.

Silencing of SlMYB50 affects tolerance to drought and salt stress in tomato

High salinity and drought stresses often cause plants to produce ROS, including hydrogen peroxide (H₂O₂) and superoxide (O₂^-), which interfere with plant growth and affect crop yield. The transcription factors of the MYB family are involved in responses to biotic and abiotic stresses. Here, we isolated the R2R3-MYB transcription factor gene SlMYB50 and found that silencing of SlMYB50 increased resistance to PEG 6000, mannitol and salt. In addition, the resistance of transgenic tomatoes increased under high salt and drought stress. After stress treatment, the relative water content, chlorophyll content (critical for carbon fixation) and root vitality of the SlMYB50-RNAi lines were higher than those of the wild-type (WT). The opposite was true the water loss rate, relative conductivity, and MDA (as a sign of cell wall disruption). Under drought stress conditions, SlMYB50-silenced lines exhibited less H₂O₂ and less O₂^- accumulation, as well as higher CAT enzyme activity, than were exhibited by the WT. Notably, after stress treatment, the expression levels of chlorophyll-synthesis-related, flavonoid-synthesis-related, carotenoid-related, antioxidant-enzyme-related and ABA-biosynthesis-related genes were all upregulated in SlMYB50-silenced lines compared to those of WT. A dual-luciferase reporter system was used to verify that SlMYB50 could bind to the CHS1 promoter. In summary, this study identified essential roles for SlMYB50 in regulating drought and salt tolerance.

Rice apoplastic CBM1-interacting protein counters blast pathogen invasion by binding conserved carbohydrate binding module 1 motif of fungal proteins

When infecting plants, fungal pathogens secrete cell wall-degrading enzymes (CWDEs) that break down cellulose and hemicellulose, the primary components of plant cell walls. Some fungal CWDEs contain a unique domain, named the carbohydrate binding module (CBM), that facilitates their access to polysaccharides. However, little is known about how plants counteract pathogen degradation of their cell walls. Here, we show that the rice cysteine-rich repeat secretion protein OsRMC binds to and inhibits xylanase MoCel10A of the blast fungus pathogen Magnaporthe oryzae, interfering with its access to the rice cell wall and degradation of rice xylan. We found binding of OsRMC to various CBM1-containing enzymes, suggesting that it has a general role in inhibiting the action of CBM1. OsRMC is localized to the apoplast, and its expression is strongly induced in leaves infected with M. oryzae. Remarkably, knockdown and overexpression of OsRMC reduced and enhanced rice defense against M. oryzae, respectively, demonstrating that inhibition of CBM1-containing fungal enzymes by OsRMC is crucial for rice defense. We also identified additional CBM-interacting proteins (CBMIPs) from Arabidopsis thaliana and Setaria italica, indicating that a wide range of plants counteract pathogens through this mechanism.

Plants have evolved various activity-inhibiting proteins as a defense against fungal cell wall-degrading enzymes (CWDEs), but how plants counteract the function of fungal enzymes containing carbohydrate binding modules (CBMs) remains unknown. Here, we demonstrate that OsRMC, a member of the cysteine-rich repeat secretion protein family, interacts with fungal CBM1. OsRMC binding to CBM1 of a blast fungal xylanase blocks access to cellulose, resulting in the inhibition of xylanase enzymatic activity. Our study provides significant insights into plant countermeasures against CWDEs in the apoplastic space during plant-fungal pathogen interactions. It also reveals a molecular function of the DUF26 domain widely distributed in plant proteins.

The transcription factor OsMYBc and an E3 ligase regulate expression of a K+ transporter during salt stress

Sodium (Na+) and potassium (K+) homeostasis is essential for plant survival in saline soils. A member of the High-Affinity K+ Transporter (HKT) family in rice (Oryza sativa), OsHKT1;1, is a vital regulator of Na+ exclusion from shoots and is bound by a MYB transcription factor (OsMYBc). Here, we generated transgenic rice lines in the oshkt1;1 mutant background for genetic complementation using genomic OsHKT1;1 containing a native (Com) or mutated (mCom) promoter that cannot be bound by OsMYBc. In contrast to wild-type (WT) or Com lines, the mCom lines were not able to recover the salt-sensitive phenotype of oshkt1;1. The OsMYBc-overexpressing plants were more tolerant to salt stress than WT plants. A yeast two-hybrid screen using the OsMYBc N-terminus as bait identified a rice MYBc stress-related RING finger protein (OsMSRFP). OsMSRFP is an active E3 ligase that ubiquitinated OsMYBc in vitro and mediated 26S proteasome-mediated degradation of OsMYBc under semi-in vitro and in vivo conditions. OsMSRFP attenuated OsMYBc-mediated OsHKT1;1 expression, and knockout of OsMSRFP led to rice salt tolerance. These findings uncover a regulatory mechanism of salt response that fine-tunes OsHKT1;1 transcription by ubiquitination of OsMYBc.

Molecular mechanisms underlying host-induced gene silencing

Host-induced gene silencing (HIGS) refers to the silencing of genes in pathogens and pests by expressing homologous double-stranded RNAs (dsRNA) or artificial microRNAs (amiRNAs) in the host plant. The discovery of such trans-kingdom RNA silencing has enabled the development of RNA interference-based approaches for controlling diverse crop pathogens and pests. Although HIGS is a promising strategy, the mechanisms by which these regulatory RNAs translocate from plants to pathogens, and how they induce gene silencing in pathogens, are poorly understood. This lack of understanding has led to large variability in the efficacy of various HIGS treatments. This variability is likely due to multiple factors, such as the ability of the target pathogen or pest to take up and/or process RNA from the host, the specific genes and target sequences selected in the pathogen or pest for silencing, and where, when, and how the dsRNAs or amiRNAs are produced and translocated. In this review, we summarize what is currently known about the molecular mechanisms underlying HIGS, identify key unanswered questions, and explore strategies for improving the efficacy and reproducibility of HIGS treatments in the control of crop diseases.

Ectopic expression of BrIQD35 promotes drought stress tolerance in Nicotiana benthamiana

The plant IQD gene family is responsive to a variety of stresses. In this study, we studied the structural features and functions of the gene BrIQD35 in Chinese cabbage, a member of the IQD gene family. BrIQD35 was cloned and shown to contain an IQ motif. Transient expression of BrIQD35 indicated that it was localized on the plasma membrane and was significantly upregulated under drought and salt stress in Chinese cabbage. To further identify the function of BrIQD35, it was heterologously overexpressed in Nicotiana benthamiana. Although there was no significant difference between BrIQD35-overexpressed and wild-type (WT) plants under salt stress, WT N. benthamiana showed more wilting than the BrIQD35-overexpressed plants under drought stress. Since the IQ motif has been annotated as a CaM binding site, yeast two-hybrid assays were used to explore the interaction between BrIQD35 and CaM. The results indicated that BrIQD35 interacts weakly with CaMb, but not with CaMa, suggesting that BrIQD35 may function through the Ca2+ -CaMb pathway. The findings reveal a novel gene involved in drought tolerance, which is important for plant breeding and quality improvement for Chinese cabbage.

TMT-based quantitative membrane proteomics identified PRRs potentially involved in the perception of MSP1 in rice leaves

Pathogen-associated molecular patterns (PAMPs) play a key role in triggering PAMPs triggered immunity (PTI) in plants. In the case of the rice-Magnaporthe oryzae pathosystem, fewer PAMPs and their pattern recognition receptors (PRRs) have been characterized. Recently, a M. oryzae snodprot1 homolog protein (MSP1) has been identified that functions as PAMP and triggering the PTI responses in rice. However, the molecular mechanism underlying MSP1-induced PTI is currently elusive. Therefore, we generated MSP1 overexpressed transgenic lines of rice, and a tandem mass tag (TMT)-based quantitative membrane proteomic analysis was employed to decipher the potential MSP1-induced signaling in rice using total cytosolic as well as membrane protein fractions. This approach led to the identification of 8033 proteins of which 1826 were differentially modulated in response to overexpression of MSP1 and/or exogenous jasmonic acid treatment. Of these, 20 plasma membrane-localized receptor-like kinases (RLKs) showed increased abundance in MSP1 overexpression lines. Moreover, activation of proteins related to the protein degradation and modification, calcium signaling, redox, and MAPK signaling was observed in transgenic lines expressing MSP1 in the apoplast. Taken together, our results identified potential PRR candidates involved in MSP1 recognition and suggested the overview mechanism of the MSP1-induced PTI signaling in rice leaves. SIGNIFICANCE: In plants, recognition of pathogen pathogen-derived molecules, such as PAMPs, by plant plant-derived PRRs has an essential role for in the activation of PTI against pathogen invasion. Typically, PAMPs are recognized by plasma membrane (PM) localized PRRs, however, identifying the PM-localized PRR proteins is challenging due to their low abundance. In this study, we performed an integrated membrane protein enrichment by microsomal membrane extraction (MME) method and subsequent TMT-labeling-based quantitative proteomic analysis using MSP1 overexpressed rice. Based on these results, we successfully identified various intracellular and membrane membrane-localized proteins that participated in the MSP1-induced immune response and characterized the potential PM-localized PRR candidates in rice.

A NAC Transcription Factor from 'Sea Rice 86' Enhances Salt Tolerance by Promoting Hydrogen Sulfide Production in Rice Seedlings

Soil salinity severely threatens plant growth and crop performance. Hydrogen sulfide (H₂S), a plant signal molecule, has been implicated in the regulation of plant responses to salinity stress. However, it is unclear how the transcriptional network regulates H₂S biosynthesis during salt stress response. In this study, we identify a rice NAC (NAM, ATAF and CUC) transcription factor, OsNAC35-like (OsNACL35), from a salt-tolerant cultivar ‘Sea Rice 86′ (SR86) and further show that it may have improved salt tolerance via enhanced H₂S production. The expression of OsNACL35 was significantly upregulated by high salinity and hydrogen peroxide (H₂O₂). The OsNACL35 protein was localized predominantly in the nucleus and was found to have transactivation activity in yeast. The overexpression of OsNACL35 (OsNACL35-OE) in japonica cultivar Nipponbare ramatically increased resistance to salinity stress, whereas its dominant-negative constructs (SUPERMAN repression domain, SRDX) conferred hypersensitivity to salt stress in the transgenic lines at the vegetative stage. Moreover, the quantitative real-time PCR analysis showed that many stress-associated genes were differentially expressed in the OsNACL35-OE and OsNACL35-SRDX lines. Interestingly, the ectopic expression of OsNACL35 triggered a sharp increase in H₂S content by upregulating the expression of a H₂S biosynthetic gene, OsDCD1, upon salinity stress. Furthermore, the dual luciferase and yeast one-hybrid assays indicated that OsNACL35 directly upregulated the expression of OsDCD1 by binding to the promoter sequence of OsDCD1. Taken together, our observations illustrate that OsNACL35 acts as a positive regulator that links H₂S production to salt stress tolerance, which may hold promising utility in breeding salt-tolerant rice cultivar.

A Review of Integrative Omic Approaches for Understanding Rice Salt Response Mechanisms

Soil salinity is one of the most serious environmental challenges, posing a growing threat to agriculture across the world. Soil salinity has a significant impact on rice growth, development, and production. Hence, improving rice varieties’ resistance to salt stress is a viable solution for meeting global food demand. Adaptation to salt stress is a multifaceted process that involves interacting physiological traits, biochemical or metabolic pathways, and molecular mechanisms. The integration of multi-omics approaches contributes to a better understanding of molecular mechanisms as well as the improvement of salt-resistant and tolerant rice varieties. Firstly, we present a thorough review of current knowledge about salt stress effects on rice and mechanisms behind rice salt tolerance and salt stress signalling. This review focuses on the use of multi-omics approaches to improve next-generation rice breeding for salinity resistance and tolerance, including genomics, transcriptomics, proteomics, metabolomics and phenomics. Integrating multi-omics data effectively is critical to gaining a more comprehensive and in-depth understanding of the molecular pathways, enzyme activity and interacting networks of genes controlling salinity tolerance in rice. The key data mining strategies within the artificial intelligence to analyse big and complex data sets that will allow more accurate prediction of outcomes and modernise traditional breeding programmes and also expedite precision rice breeding such as genetic engineering and genome editing.

The AP2/ERF transcription factor SlERF.F5 functions in leaf senescence in tomato

Our results confirmed that SlERF.F5 can directly regulate the promoter activity of ACS6 and interact with SlMYC2 to regulate tomato leaf senescence. The process of plant senescence is complex and highly coordinated, and is regulated by many endogenous and environmental signals. Ethylene and jasmonic acid are well-known senescence inducers, but their molecular mechanisms for inducing leaf senescence have not been fully elucidated. Here, we isolated an ETHYLENE RESPONSE FACTOR F5 (SlERF.F5) from tomato. Silencing of SlERF.F5 causes accelerated senescence induced by age, darkness, ethylene, and jasmonic acid. However, overexpression of SlERF.F5 would not promote senescence. Moreover, SlERF.F5 can regulate the promoter activity of ACS6 in vitro and in vivo. Suppression of SlERF.F5 resulted in increased sensitivity to ethylene and jasmonic acid, decreased accumulation of chlorophyll content, and inhibited the expression of chlorophyll- and light response-related genes. Compared with the wild type, the qRT-PCR analysis showed the expression levels of genes related to the ethylene biosynthesis pathway and the jasmonic acid signaling pathway in SlERF.F5-RNAi lines increased. Yeast two-hybrid experiments showed that SlERF.F5 and SlMYC2 (a transcription factor downstream of the JA receptor) can interact physically, thereby mediating the role of SlERF.F5 in jasmonic acid-induced leaf senescence. Collectively, our research provides new insights into how ethylene and jasmonic acid promote leaf senescence in tomato.

A Transcriptomic Analysis of Stylo [Stylosanthes guianensis (Aubl) Sw.] Provides Novel Insights Into the Basis of Salinity Tolerance

Tropical areas have a large distribution of saline soils and tidal flats with a high salinity level. Salinity stress is a key factor limiting the widespread use of tropical forage such as Stylosanthes guianensis (Aubl) Sw. This study was designed to screen the salinity tolerance of 84 S. guianensis accessions; In a greenhouse experiment, plants were subjected to Hoagland solution or Hoagland solution with 200 mM NaCl for up to 15 days. Salinity tolerant accession CIAT11365 and salinity sensitive accession FM05-2 were obtained based on withered leaf rate (WLR). Further verification of salinity tolerance in CIAT11365 and FM05-2 with different salinity gradients showed that salinity stress increased WLR and decreased relative chlorophyll content (SPAD), maximum photochemical efficiency of photosystem II (Fv/Fm), and photosynthetic rate (Pn) in FM05-2, but CIAT11365 exhibited lower WLR and higher SPAD, Fv/Fm, and Pn. Leaf RNA-Seq revealed that Ca2+ signal transduction and Na+ transport ability, salinity tolerance-related transcription factors and antioxidant ability, an increase of auxin, and inhibition of cytokinin may play key roles in CIAT11365 response to salinity stress. The results of this study may contribute to our understanding of the molecular mechanism underlying the responses of S. guianensis to salinity stress and also provide important clues for further study and in-depth characterization of salinity resistance breeding candidate genes in S. guianensis.

How salt stress-responsive proteins regulate plant adaptation to saline conditions

An overview is presented of recent advances in our knowledge of candidate proteins that regulate various physiological and biochemical processes underpinning plant adaptation to saline conditions. Salt stress is one of the environmental constraints that restrict plant distribution, growth and yield in many parts of the world. Increased world population surely elevates food demands all over the globe, which anticipates to add a great challenge to humanity. These concerns have necessitated the scientists to understand and unmask the puzzle of plant salt tolerance mechanisms in order to utilize various strategies to develop salt tolerant crop plants. Salt tolerance is a complex trait involving alterations in physiological, biochemical, and molecular processes. These alterations are a result of genomic and proteomic complement readjustments that lead to tolerance mechanisms. Proteomics is a crucial molecular tool that indicates proteins expressed by the genome, and also identifies the functions of proteins accumulated in response to salt stress. Recently, proteomic studies have shed more light on a range of promising candidate proteins that regulate various processes rendering salt tolerance to plants. These proteins have been shown to be involved in photosynthesis and energy metabolism, ion homeostasis, gene transcription and protein biosynthesis, compatible solute production, hormone modulation, cell wall structure modification, cellular detoxification, membrane stabilization, and signal transduction. These candidate salt responsive proteins can be therefore used in biotechnological approaches to improve tolerance of crop plants to salt conditions. In this review, we provided comprehensive updated information on the proteomic data of plants/genotypes contrasting in salt tolerance in response to salt stress. The roles of salt responsive proteins that are potential determinants for plant salt adaptation are discussed. The relationship between changes in proteome composition and abundance, and alterations observed in physiological and biochemical features associated with salt tolerance are also addressed.

In Silico and Transcription Analysis of Trehalose-6-phosphate Phosphatase Gene Family of Wheat: Trehalose Synthesis Genes Contribute to Salinity, Drought Stress and Leaf Senescence

Trehalose-6-phosphate phosphatase (TPP) genes take part in trehalose metabolism and also in stress tolerance, which has been well documented in many species but poorly understood in wheat. The present research has identified a family of 31 TPP genes in Triticum aestivum L. through homology searches and classified them into five clades by phylogenetic tree analysis, providing evidence of an evolutionary status with Hordeum vulgare, Brachypodium distachyon and Oryza sativa. The exon-intron distribution revealed a discrete evolutionary history and projected possible gene duplication occurrences. Furthermore, different computational approaches were used to analyze the physical and chemical properties, conserved domains and motifs, subcellular and chromosomal localization, and three-dimensional (3-D) protein structures. Cis-regulatory elements (CREs) analysis predicted that TaTPP promoters consist of CREs related to plant growth and development, hormones, and stress. Transcriptional analysis revealed that the transcription levels of TaTPPs were variable in different developmental stages and organs. In addition, qRT-PCR analysis showed that different TaTPPs were induced under salt and drought stresses and during leaf senescence. Therefore, the findings of the present study give fundamental genomic information and possible biological functions of the TaTPP gene family in wheat and will provide the path for a better understanding of TaTPPs involvement in wheat developmental processes, stress tolerance, and leaf senescence.

Regional Heritability Mapping of Quantitative Trait Loci Controlling Traits Related to Growth and Productivity in Popcorn (Zea mays L.)

The method of regional heritability mapping (RHM) has become an important tool in the identification of quantitative trait loci (QTLs) controlling traits of interest in plants. Here, RHM was first applied in a breeding population of popcorn, to identify the QTLs and candidate genes involved in grain yield, plant height, kernel popping expansion, and first ear height, as well as determining the heritability of each significant genomic region. The study population consisted of 98 S1 families derived from the 9th recurrent selection cycle (C-9) of the open-pollinated variety UENF-14, which were genetically evaluated in two environments (ENV1 and ENV2). Seventeen and five genomic regions were mapped by the RHM method in ENV1 and ENV2, respectively. Subsequent genome-wide analysis based on the reference genome B73 revealed associations with forty-six candidate genes within these genomic regions, some of them are considered to be biologically important due to the proteins that they encode. The results obtained by the RHM method have the potential to contribute to knowledge on the genetic architecture of the growth and yield traits of popcorn, which might be used for marker-assisted selection in breeding programs.

Membrane localized thaumatin-like protein from tea (CsTLP) enhanced seed yield and the plant survival under drought stress in Arabidopsis thaliana

Thaumatin-like proteins (TLPs) are pathogenesis-related (PR5) proteins, which are induced in response to various biotic and abiotic stresses. The present work was carried out to clone TLP of Camellia sinensis (CsTLP) and to evaluate the response of transgenic lines of Arabidopsis constitutively expressing CsTLP under drought conditions. Data showed that transgenic lines exhibited lower relative electrolyte leakage and higher water retention capacity as compared to the wild-type (WT) plants under drought stress. In addition, results with confocal microscopy showed CsTLP + GFP fusion protein to be localized in the cell membrane which moved to the intercellular spaces under prolonged drought stress. Expression of CsTLP enhanced seed yield and the plant survival in transgenic lines as compared to the WT plants under drought stress. Results suggested the importance of CsTLP in improving drought tolerance in Arabidopsis.

CRISPR-Cas technology based genome editing for modification of salinity stress tolerance responses in rice (Oryza sativa L.)

Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein (Cas) technology is an effective tool for site-specific genome editing, used to precisely induce mutagenesis in different plant species including rice. Salinity is one of the most stressful environmental constraints affecting agricultural productivity worldwide. As plant adaptation to salinity stress is under polygenic control therefore, 51 rice genes have been identified that play crucial role in response to salinity. This review offers an exclusive overview of genes identified in rice genome for salinity stress tolerance. This will provide an idea to produce rice varieties with enhanced salt tolerance using the potentially efficient CRISPR-Cas technology. Several undesirable off-target effects of CRISPR-Cas technology and their possible solutions have also been highlighted.

Phenolic compound abundance in Pak choi leaves is controlled by salinity and dependent on pH of the leaf apoplast

Onset of salinity induces the pH of the leaf apoplast of Pak choi transiently to increase over a period of 2 to 3 hr. This pH event causes protein abundances in leaves to increase. Among them are enzymes that are key for the phenylpropanoid pathway. To answer the questions whether this short-term salt stress also influences contents of the underlying phenylpropanoids and for clarifying as to whether the apoplastic pH transient plays a role for such a putative effect, Pak choi plants were treated with 37.5 mM CaCl2 against a non-stressed control. A third experimental group, where the leaf apoplast of plants treated with 37.5 mM CaCl2, was clamped in the acidic range by means of infiltration of 5 mM citric acid/sodium citrate (pH 3.6), enabled validation of pH-dependent effects. Microscopy-based live cell imaging was used to quantify leaf apoplastic pH in planta. Phenolics were quantified shortly after the formation of the leaf apoplastic pH transient by means of HPLC-DAD-ESI-MS. Results showed that different phenolic compounds were modulated at 150 and 200 min after the onset of chloride salinity. A pH-independent reduction in phenolic acid abundance as well as an accumulation of phenolic acid:malate conjugates was quantified after 200 min of salt stress. However, at 150 min after the onset of salt stress, flavonoids were significantly reduced by salinity in a pH-dependent manner. These results provided a strong indication that the pH of the apoplast is a relevant component for the short-term metabolic response to chloride salinity.

Metabolite Profile of Xylem Sap in Cotton Seedlings Is Changed by K Deficiency

Xylem sap, belonging to the plant apoplast, not only provides plant tissues with inorganic and organic substances but also facilitates communication between the roots and the leaves and coordinates their development. This study investigated the effects of potassium (K) deficiency on the morphology and the physiology of cotton seedlings as well as pH, mineral nutrient contents, and metabolites of xylem sap. In particular, we compared changes in root-shoot communication under low K (LK) and normal K (NK, control) levels. Compared to control, LK stress significantly decreased seedling biomass (leaf, stem, and root dry weight; stem and root length; root surface area and root volume) and the levels of K, Na (sodium), Mg (magnesium), Fe (iron), and Zn (zinc) in xylem sap. A total of 82 metabolites in sap analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) showed significant differences between the two conditions; among these, 38 were up-regulated more than 2-fold, while the others were down-regulated less than 0.5-fold. In particular, several metabolites found in the cell membrane including three cholines (glycerophosphatecholine, 2-hexenylcholine, and caproylcholine) and desglucocoroloside and others such as malondialdehyde, α-amino acids and derivatives, sucrose, and sugar alcohol significantly increased under LK stress, indicating that cell membranes were damaged and protein metabolism was abnormal. It is worth noting that glycerophosphocholine was up-regulated 29-fold under LK stress, indicating that it can be used as an important signal of root-shoot communication. Furthermore, in pathway analyses, 26 metabolites were matched to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways; L-aspartic acid, which was associated with 10 KEGG pathways, was the most involved metabolite. Overall, K deficiency reduced the antioxidant capacity of cotton seedlings and led to a metabolic disorder including elevated levels of primary metabolites and inhibited production of secondary metabolites. This eventually resulted in decreased biomass of cotton seedlings under LK stress. This study lays a solid foundation for further research on targeted metabolites and signal substances in the xylem sap of cotton plants exposed to K deficiency.

CRISPR/Cas9 targeted mutagenesis of SlLBD40, a lateral organ boundaries domain transcription factor, enhances drought tolerance in tomato

The LATERAL ORGAN BOUNDARIES DOMAIN (LBD)-containing genes are plant-specific genes that play important roles in lateral organ development. In this study, we identified LBD40 (Solyc02g085910), which belongs to subfamily II of the LBD family of genes in tomato. LBD40 was highly expressed in roots and fruit. LBD40 expression was significantly induced by PEG and salt. Moreover, SlLBD40 expression was induced by methyl jasmonate treatment, while SlLBD40 expression could not be induced in the jasmonic acid-insensitive1 (jai1) mutant or MYC2-silenced plants, in which jasmonic acid (JA) signaling was disrupted. These findings demonstrate that SlLBD40 expression was dependent on JA signaling and that it might be downstream of SlMYC2, which is the master transcription factor in the JA signal transduction pathway. Overexpressing and CRISPR/Cas9 mediated knockout transgenic tomato plants were generated to explore SlLBD40 function. The drought tolerance test showed that two SlLBD40 knockout lines wilted slightly, while SlLBD40 overexpressing plants suffered severe wilting. The statistical water loss rate and midday leaf water potential also confirmed that knockout of SlLBD40 improved the water-holding ability of tomato under drought conditions. Taken together, our study demonstrates that SlLBD40, involved in JA signaling, was a negative regulator of drought tolerance and that knockout of SlLBD40 enhanced drought tolerance in tomato. This study also provides a novel function of SlLBD40, which belongs to subfamily II of LBD genes.

Genome-Wide Characterization of OFP Family Genes in Wheat (Triticum aestivum L.) Reveals That TaOPF29a-A Promotes Drought Tolerance

OVATE family proteins (OFPs) are plant-specific transcription factors that play important roles in plant development. Although common wheat (Triticum aestivum L.) is a major staple food worldwide, OFPs have not been systematically analyzed in this important crop. Here, we performed a genome-wide survey of OFP genes in wheat and identified 100 genes belonging to 34 homoeologous groups. Arabidopsis thaliana, rice (Oryza sativa), and wheat OFP genes were divided into four subgroups based on their phylogenetic relationships. Structural analysis indicated that only four TaOFPs contain introns. We mapped the TaOFP genes onto the wheat chromosomes and determined that TaOFP17 was duplicated in this crop. A survey of cis-acting elements along the promoter regions of TaOFP genes suggested that subfunctionalization of homoeologous genes might have occurred during evolution. The TaOFPs were highly expressed in wheat, with tissue- or organ-specific expression patterns. In addition, these genes were induced by various hormone and stress treatments. For instance, TaOPF29a-A was highly expressed in roots in response to drought stress. Wheat plants overexpressing TaOPF29a-A had longer roots and higher dry weights than nontransgenic plants under drought conditions, suggesting that this gene improves drought tolerance. Our findings provide a starting point for further functional analysis of this important transcription factor family and highlight the potential of using TaOPF29a-A to genetically engineer drought-tolerant crops.

Suppression of a hexokinase gene, SlHXK1, leads to accelerated leaf senescence and stunted plant growth in tomato

Sugars are the key regulatory molecules that impact diverse biological processes in plants. Hexokinase, the key rate-limiting enzyme in hexose metabolism, takes part in the first step of glycolytic pathway. Acting as a sensor that mediates sugar regulation, hexokinase has been proved to play significant roles in regulating plant growth and development. Here, we isolated a hexokinase gene SlHXK1 from tomato. Its transcript levels were higher in flowers and leaves than in other organs and decreased during leaf and petiole development. SlHXK1-RNAi lines displayed advanced leaf senescence and stunted plant growth. Physiological features including plant height, leaf length, thickness and size, the contents of chlorophyll, starch and MDA, and hexokinase activity were dramatically altered in SlHXK1-RNAi plants. Dark-induced leaf senescence were advanced and the transcripts of senescence-related genes after darkness treatment were markedly increased in SlHXK1-RNAi plants. RNA-seq and qRT-PCR analyses showed that the transcripts of genes related to plant hormones, photosynthesis, chloroplast development, chlorophyll synthesis and metabolism, cellular process, starch and sucrose metabolism, and senescence were significantly altered in SlHXK1-RNAi plants. Taken together, our data demonstrate that SlHXK1 is a significant gene involved in leaf senescence and plant growth and development in tomato through affecting starch turnover.

Phytoremediation of acetochlor residue by transgenic Arabidopsis expressing the acetochlor N-dealkylase from Sphingomonas wittichii DC-6

Transgenic engineering is an effective way for plants to obtain strong degradation or detoxification abilities to target pollutants. Acetochlor is an important and widely used herbicide, however, its residue is persistent in soil and is toxic to humans and rotation crops. In this study, the degradation ability and tolerance to acetochlor of transgenic Arabidopsis thaliana synthesizing the oxygenase component, CndA, of the bacterial acetochlor N-dealkylase system, CndABC, were investigated. Two transgenic plants, including a cytoplasm transformant, in which the CndA was located in the cytoplasm, and a chloroplast transformant, in which the CndA was located in the chloroplast, were constructed. The cytoplasm transformant acquired only weak acetochlor degradation activity and displayed little acetochlor tolerance. In contrast, the chloroplast transformant exhibited high degradation efficiency and strong tolerance to acetochlor; it could transform 94.3% of 20 μM acetochlor in water within 48 h and eliminate 80.2% of 5 mg/kg acetochlor in soil within 30 d. The metabolite of acetochlor N-dealkylation catalyzed by CndA, 2-chloro-N-(2-methyl-6-ethylphenyl)acetamide (CMEPA), could be released outside the cells by chloroplast transformant and further degraded by indigenous microorganisms in the soil. This study provides an effective strategy for the phytoremediation of acetochlor residue in water and soil.

A novel cysteine-rich receptor-like kinase gene, TaCRK2, contributes to leaf rust resistance in wheat

Leaf rust, caused by Puccinia triticina, is one of the most destructive fungal diseases in wheat production worldwide. The hypersensitive reaction (HR) is an important defence response against P. triticina infection. In this study, the physiological races 165 and 260 of P. triticina were combined with a line derived from the bread wheat cultivar Thatcher with the leaf rust resistance locus Lr26 to form compatible and incompatible combinations, respectively. Based on an RNA-Seq database of the interaction systems, a new wheat cysteine-rich receptor-like kinase gene, TaCRK2, is specifically induced and up-regulated in the incompatible combination. We identified that TaCRK2 was regulated in a Ca²⁺ -dependent manner. Knockdown of TaCRK2 by virus-induced gene silencing and RNAi leads to a dramatic increase in HR area and the number of haustorial mother cells at the single infection site. In addition, urediniospores, a P. triticina-specific pathogenic marker in compatible combinations, were observed on leaf surfaces of silenced plants at approximately 15 days after inoculation in the incompatible combination. Moreover, transcription levels of TaPR1, TaPR2, and TaPR5 were obviously reduced in TaCRK2-silenced plants. TaCRK2 overexpression in Nicotiana benthamiana induced strong HR-like cell death. Finally, transient expression of green fluorescent protein fused with TaCRK2 in N. benthamiana indicated that TaCRK2 localizes in the endoplasmic reticulum. Thus, TaCRK2 plays an important role in the resistance to P. triticina infection and has a positive regulation effect on the HR cell death process induced by P. triticina.

Physiological and proteomic responses of reactive oxygen species metabolism and antioxidant machinery in mulberry (Morus alba L.) seedling leaves to NaCl and NaHCO3 stress

In this paper, the effects of 100 mM NaCl and NaHCO₃ stress on reactive oxygen species (ROS) and physiological and proteomic aspects of ROS metabolism in mulberry seedling leaves were studied. The results showed that NaCl stress had little effect on photosynthesis and respiration of mulberry seedling leaves. Superoxide dismutase (SOD) activity and the expression of related proteins in leaves increased by varying degrees, and accumulation of superoxide anion (O₂·^-) not observed. Under NaHCO₃ stress, photosynthesis and respiration were significantly inhibited, while the rate of O₂·^- production rate and H₂O₂ content increased. The activity of catalase (CAT) and the expression of CAT (W9RJ43) increased under NaCl stress. In response to NaHCO₃ stress, the activity and expression of CAT were significantly decreased, but the ability of H₂O₂ scavenging of peroxidase (POD) was enhanced. The ascorbic acid-glutathione (AsA-GSH) cycle in mulberry seedling leaves was enhancement in both NaCl and NaHCO₃ stress. The expression of 2-Cys peroxiredoxin BAS1 (2-Cys Prx BAS1), together with thioredoxin F (TrxF), thioredoxin O1 (TrxO1), thioredoxin-like protein CITRX (Trx CITRX), and thioredoxin-like protein CDSP32 (Trx CDSP32) were significantly increased under NaCl stress. Under NaHCO₃ stress, the expression of the electron donor of ferredoxin-thioredoxin reductase (FTR), together with Trx-related proteins, such as thioredoxin M (TrxM), thioredoxin M4 (TrxM4), thioredoxin X (TrxX), TrxF, and Trx CSDP32 were significantly decreased, suggesting that the thioredoxin-peroxiredoxin (Trx-Prx) pathway's function of scavenging H₂O₂ of in mulberry seedling leaves was inhibited. Taken together, under NaCl stress, excessive production of O₂·^- mulberry seedlings leaves was inhibited, and H₂O₂ was effectively scavenged by CAT, AsA-GSH cycle and Trx-Prx pathway. Under NaHCO₃ stress, despite the enhanced functions of POD and AsA-GSH cycle, the scavenging of O₂·^- by SOD was not effective, and that of H₂O₂ by CAT and Trx-Prx pathway were inhibited; and in turn, the oxidative damage to mulberry seedling leaves could not be reduced.

Traditional rice landraces in Lei-Qiong area of South China tolerate salt stress with strong antioxidant activity

Salt stress, causing serious loss on crop productions, is one of the most important environmental stresses throughout the world. The aim of this study is to select salt-tolerant traditional rice resources collected from Lei-Qiong area of South China and investigate their physiological performances and biochemical regulations during salt stress response, together with two well-known international varieties, Nona Bokra (salt-tolerant sample) and IR29 (salt-sensitive sample). After comprehensive analyses, we discovered that two Lei-Qiong traditional salt-tolerant rice samples showed less growth inhibition by salt stress during both germination and seedling stage, in comparison with other rice samples. Moreover, there were less chlorosis symptoms in these two kinds of salt tolerant rice under salt stress, corresponding to their better water-holding capacity. We measured malondialdehyde and proline contents, and activities of CAT and POD of seedlings treated with 100 mM NaCl for 5 dand 10 d, respectively. Interestingly, less cellular membrane damage and stronger antioxidant enzyme system were found in the two Lei-Qiong rice samples. Our study suggests that traditional rice landrace growing onshore of Lei-Qiong area in China possesses good salt-tolerant capacity, which could be attributed to their efficient antioxidant enzyme system.

Protein Extraction, Enrichment and MALDI MS and MS/MS Analysis from Bitter Orange Leaves (Citrus aurantium)

Citrus aurantium is a widespread tree in the Mediterranean area, and it is mainly used as rootstock for other citrus. In the present study, a vacuum infiltration centrifugation procedure, followed by solid phase extraction matrix-assisted laser desorption ionization tandem mass spectrometry (SPE MALDI MS/MS) analysis, was adopted to isolate proteins from leaves. The results of mass spectrometry (MS) profiling, combined with the top-down proteomics approach, allowed the identification of 78 proteins. The bioinformatic databases TargetP, SignalP, ChloroP, WallProtDB, and mGOASVM-Loc were used to predict the subcellular localization of the identified proteins. Among 78 identified proteins, 20 were targeted as secretory pathway proteins and 36 were predicted to be in cellular compartments including cytoplasm, nucleus, and cell membrane. The largest subcellular fraction was the secretory pathway, accounting for 25% of total proteins. Gene Ontology (GO) of Citrus sinensis was used to simplify the functional annotation of the proteins that were identified in the leaves. The Kyoto Encyclopedia of Genes and Genomes (KEGG) showed the enrichment of metabolic pathways including glutathione metabolism and biosynthesis of secondary metabolites, suggesting that the response to a range of environmental factors is the key processes in citrus leaves. Finally, the Lipase GDSL domain-containing protein GDSL esterase/lipase, which is involved in plant development and defense response, was for the first time identified and characterized in Citrus aurantium.

Ectopic Expression of Gs5PTase8, a Soybean Inositol Polyphosphate 5-Phosphatase, Enhances Salt Tolerance in Plants

Inositol polyphosphate 5-phosphatases (5PTases) function in inositol signaling by regulating the catabolism of phosphoinositol derivatives. Previous reports showed that 5PTases play a critical role in plant development and stress responses. In this study, we identified a novel 5PTase gene, Gs5PTase8, from the salt-tolerance locus of chromosome 3 in wild soybean (Glycine soja). Gs5PTase8 is highly up-regulated under salt treatment. It is localized in the nucleus and plasma membrane with a strong signal in the apoplast. Ectopic expression of Gs5PTase8 significantly increased salt tolerance in transgenic BY-2 cells, soybean hairy roots and Arabidopsis, suggesting Gs5PTase8 could increase salt tolerance in plants. The overexpression of Gs5PTase8 significantly enhanced the activities of catalase and ascorbate peroxidase under salt stress. The seeds of Gs5PTase8-transgenic Arabidopsis germinated earlier than the wild type under abscisic acid treatment, indicating Gs5PTase8 would alter ABA sensitivity. Besides, transcriptional analyses showed that the stress-responsive genes, AtRD22, AtRD29A and AtRD29B, were induced with a higher level in the Gs5PTase8-transgenic Arabidopsis plants than in the wild type under salt stress. These results reveal that Gs5PTase8 play a positive role in salt tolerance and might be a candidate gene for improving soybean adaptation to salt stress.

OsSPL10, a SBP-Box Gene, Plays a Dual Role in Salt Tolerance and Trichome Formation in Rice (Oryza sativa L.)

Salinity is one of the major abiotic stress factors limiting rice production. Glabrousness is a trait of agronomic importance in rice (Oryza sativa L.). We previously found a single-gene recessive mutant sst, which displayed increased salt tolerance and glabrous leaf and glume without trichomes, and identified an SBP-box gene OsSPL10 as the candidate of the SST gene. In this study, OsSPL10-knockout and OsSPL10-overexpression mutants were created to check the function of the gene. The knockout mutants exhibited enhanced salt tolerance and glabrous leaves and glumes as expected, while the overexpression mutants showed opposite phenotypes, in which both salt sensitivity and trichome density on leaf and glume were increased. These results clearly confirmed that OsSPL10 is SST, and suggested that OsSPL10 controls the initiation rather than the elongation of trichomes. In addition, expression analysis indicated that OsSPL10 was preferentially expressed in young panicle and stem, and protein OsSPL10 was localized in nucleus. Taken together, OsSPL10 negatively controls salt tolerance but positively controls trichome formation in rice.

Efficient improvement of soil salinization through phytoremediation induced by chemical remediation in extreme arid land northwest China

This study investigated the influence of chemical remediation agents (Bc, M, HA, and Bc + HA) on the growth of the halophyte Lycium ruthenicum and the mechanism of restoration of soil salinization using joint halophyte and chemical remediation in arid fields. The results showed that aboveground organ biomass of L. ruthenicum increased significantly with the chemical remediation agents analyze but the effects on the root system were different. Among the root traits, dry weight of the taproot of L. ruthenicum increased significantly (p < 0.05) by 60.57% with HA; however, the lateral roots were inhibited. With the addition of biochar, the content of sodium ions in roots increased significantly. Further analysis showed that endogenous manganese (Mn) promoted K⁺ absorption concentration increase from 22.09 to 38.28 g/kg. Moreover, Joint L. ruthenicum and chemical remediation with Bc, HA, M and Bc + HA reduced Na⁺ to 5854.76, 9396.19, 6530.95 and 11164.29 g/(kg DW⋅m²·a), respectively. Tests revealed that for L. ruthenicum, the aboveground biomass and root morphological plasticity, as well as the synergistic effect of K⁺ on Na⁺ transport capacity influenced by endogenous Mn in leaves, were the primary causes of the efficient improvement of saline-alkali land.

Novel Maize NAC Transcriptional Repressor ZmNAC071 Confers Enhanced Sensitivity to ABA and Osmotic Stress by Downregulating Stress-Responsive Genes in Transgenic Arabidopsis

NAC TFs play crucial roles in response to abiotic stresses in plants. Here, ZmNAC071 was identified as a nuclear located transcriptional repressor. Overexpression of ZmNAC071 in Arabidopsis enhanced sensitivity of transgenic plants to ABA and osmotic stress. The expression levels of SODs, PODs, P5CSs, and AtMYB61 were inhibited by ZmNAC071, which results in reduced ROS scavenging and proline content, increased ROS level, and water loss. Besides, the expression levels of some ABA or abiotic stress-related genes, like ABIs, RD29A, DREBs, and LEAs were also significantly inhibited by ZmNAC071. Yeast one-hybrid assay demonstrated that ZmNAC071 specifically bound to the cis-acting elements containing CGT[G/A] core sequences in the promoter of stress-related genes, suggesting that ZmNAC071 may participate in the regulation of transcription of these genes through recognizing the core sequences CGT[G/A]. These results will facilitate further studies concerning the cis-elements and downstream genes targeted by ZmNAC071 in maize.

GmHsp90A2 is involved in soybean heat stress as a positive regulator

Heat shock protein 90 s (Hsp90s), one of the most conserved and abundant molecular chaperones, is an essential component of the protective stress response. A previous study reported at least 12 genes in the GmHsp90s family in soybean and that GmHsp90A2 overexpression enhanced thermotolerance in Arabidopsis thaliana. Here, we investigate the roles of GmHsp90A2 in soybean by utilizing stable transgenic soybean lines overexpressing GmHsp90A2 and mutant lines generated by the CRISPR/Cas9 system. The results showed that compared with wild-type plants (WT) and empty vector control plants (VC), T3 transgenic soybean plants overexpressing GmHsp90A2 exhibited increased tolerance to heat stress through higher chlorophyll and lower malondialdehyde (MDA) contents in plants. Conversely, reduced chlorophyll and increased MDA contents in T2 homozygous GmHsp90A2-knockout mutants indicated decreased tolerance to heat stress. GmHsp90A2 was found to interact with GmHsp90A1 in yeast two-hybrid assays. Furthermore, subcellular localization analyses revealed that GmHsp90A2 was localized to the cytoplasm and cell membrane; as shown by bimolecular fluorescence complementation (BiFC) assays, GmHsp90A2 interacted with GmHsp90A1 in the nucleus and cytoplasm and cell membrane. Hence, we conclude that GmHsp90A1 is able to bind to GmHsp90A2 to form a complex and that this complex enters the nucleus. In summary, GmHsp90A2 might respond to heat stress and positively regulate thermotolerance by interacting with GmHsp90A1.

CRISPR-Cas9 directed genome engineering for enhancing salt stress tolerance in rice

Crop productivity in rice is harshly limited due to high concentration of salt in the soil. To understand the intricacies of the mechanism it is important to unravel the key pathways operating inside the plant cell. Emerging state-of-the art technologies have provided the tools to discover the key components inside the plant cell for salt tolerance. Among the molecular entities, transcription factors and/or other important components of sensing and signaling cascades have been the attractive targets and the role of NHX and SOS1 transporters amply described. Not only marker assisted programs but also transgenic approaches by using reverse genetic strategies (knockout or knockdown) or overexpression have been extensively used to engineer rice crop. CRISPR/Cas is an attractive paradigm and provides the feasibility for manipulating several genes simultaneously. Here, in this review we highlight some of the molecular entities that could be potentially targeted for generating rice amenable to sustain growth under high salinity conditions by employing CRISPR/Cas. We also try to address key questions for rice salt stress tolerance other than what is already known.

Genomic dissection and transcriptional profiling of Cysteine-rich receptor-like kinases in five cereals and functional characterization of TaCRK68-A

Cysteine-rich receptor-like kinases (CRK) constitute one of the largest subfamily of receptor-like kinases, which play crucial roles in plant development and stress response. In total, 43, 37, 36, 38 and 170 CRK genes including duplicated genes were identified in the genome of Brachypodium distachyon, Hordeum vulgare, Oryza sativa, Sorghum bicolor and Triticum aestivum, respectively. These CRK proteins were tightly clustered into four phylogenetic groups and exhibited close syntenic relationship among orthologous genes. Majority of CRK proteins contain a transmembrane domain for plasma membrane localization. The organization of exon/intron, domains and motifs were variably conserved. Tissue-specific expression suggested the involvement of certain CRK genes in plant development. Modulated expression revealed their specific stress-responsive functions. Co-expression and interaction analysis indicated their role in signaling. Ks value and divergence time analysis suggested duplication of TaCRK genes before the hybridization of T. aestivum sub-genomes. Expression comparison of duplicated TaCRK genes revealed functional retention, neofunctionalization or pseudo-functionalization. Recombinant expression of a stress-responsive gene TaCRK68-A in Escherichia coli and Saccharomyces cerevisiae displayed enhanced tolerance against heat, drought, cold and salinity stresses. The study suggested vital functions of CRKs during development and stresses, and provides the basis for functional characterization of each gene in future studies.