Salt Stress Response In Plants Research Articles

Chloroplast-localized PvBASS2 regulates salt tolerance in the C4 plant seashore paspalum.

SODIUM SYMPORTER FAMILY PROTEIN 2 (BASS2) is localized within chloroplast membranes, facilitating the translocation of pyruvate and Na+ from the cytosol to the plastid, where pyruvate supports isopentenyl diphosphate (IPP) synthesis via the methylerythritol phosphate pathway in C3 plants. Nevertheless, the biological function of BASS2 in C4 plants has not been well defined. This study unveils a previously unidentified role of PvBASS2 in Na+ and pyruvate transport in seashore paspalum (Paspalum vaginatum), a halophytic C4 grass, indicating a specific cellular function within this plant species. Data showed that overexpression of PvBASS2 in seashore paspalum attenuated salt tolerance, whereas its RNAi lines exhibited enhanced salt resistance compared to wild-type plants, suggesting a negative regulatory role of PvBASS2 in seashore paspalum salt tolerance. The constitutive overexpression of PvBASS2 was also found to reduce salt tolerance in Arabidopsis. Further study revealed that PvBASS2 negatively regulates seashore paspalum salt tolerance, possibly due to elevated Na+/K+ ratio, disrupted chloroplast structure, and reduced photosynthetic efficiency following exposure to salinity. Importantly, our subsequent investigations revealed that modulation of PvBASS2 expression in seashore paspalum influenced carbon dioxide assimilation, intermediary metabolites of the tricarboxylic acid cycle, and enzymatic activities under salinity treatment, which in turn led to alterations in free amino acid concentrations. Thus, this study reveals a role for BASS2 in the C4 plant seashore paspalum and enhances our comprehension of salt stress responses in C4 plants.

MiR319a-mediated salt stress response in poplar.

Maintenance of intracellular ion balance, especially Na+ and K+, plays an important role in plant responses to salt stress. Vessels in xylem are responsible for long-distance ion transport in vascular plants. Knowledge on the salt stress response in woody plants in limited. In this study, we identified miR319a as an important regulator in respond to salt stress in poplar. miR319a overexpression transgenic poplar showed a salt-tolerant phenotype, and cytological observation showed reduced cambium cell layers, wider xylem, increased number and lumen area of vessels and fibers, and thinner cell wall thickness in the transgenics. The miR319a-MIMIC plants, meanwhile, had opposite phenotypes, with narrower xylem, reduced number and lumen area of vessels and fibers cells, and increased wall thickness. In addition, overexpression of miR319a driven by the vessel-specific promoter significantly improved the salt tolerance compared with the fiber-specific promoter. The expression levels of PagHKT1;2 and PagSKOR1-b, which encoded high-affinity K+ and Na+ transporters for Na+ efflux and K+ influx, respectively, were positively correlated with the vessel number and lumen area. These results suggest that miR319 not only promotes ion transport rates by increasing vessel number and lumen area and reducing cell wall thickness, but also regulates the concentrations of Na+ and K+ in the xylem by up-regulating PagHKT1;2 and PagSKOR1-b. We demonstrate that miR319 may coordinate the response of poplar to salt stress through both mechanisms, enriching our understanding of the synergistic effects of the secondary xylem structure and long-distance ion transport balance in the salt tolerance of poplar.

GROWTH REGULATING FACTOR 7-mediated arbutin metabolism enhances rice salt tolerance.

Salt stress is an environmental factor that limits plant growth and crop production. With the rapid expansion of salinized arable land worldwide, investigating the molecular mechanisms underlying the salt stress response in plants is urgently needed. Here, we report that GROWTH REGULATING FACTOR 7 (OsGRF7) promotes salt tolerance by regulating arbutin (hydroquinone-β-D-glucopyranoside) metabolism in rice (Oryza sativa). Overexpression of OsGRF7 increased arbutin content, and exogenous arbutin application rescued the salt-sensitive phenotype of OsGRF7 knockdown and knockout plants. OsGRF7 directly promoted the expression of the arbutin biosynthesis genes URIDINE DIPHOSPHATE GLYCOSYLTRANSFERASE 1 (OsUGT1) and OsUGT5, and knockout of OsUGT1 or OsUGT5 reduced rice arbutin content, salt tolerance, and grain size. Furthermore, OsGRF7 degradation through its interaction with F-BOX AND OTHER DOMAINS CONTAINING PROTEIN 13 (OsFBO13) reduced rice salinity tolerance and grain size. These findings highlight an underexplored role of OsGRF7 in modulating rice arbutin metabolism, salt stress response, and grain size, as well as its broad potential use in rice breeding.

The GARP family transcription factor MtHHO3 negatively regulates salt tolerance in Medicago truncatula

High salinity is one of the detrimental environmental factors restricting plant growth and crop production throughout the world. This study demonstrated that the GARP family transcription factor MtHHO3 is involved in response to salt stress and abscisic acid (ABA) signaling in Medicago truncatula. The transcription of MtHHO3 was repressed by salt, osmotic stress, and ABA treatment. The seed germination assay showed that, overexpression of MtHHO3 in Arabidopsis thaliana caused hypersensitivity to salt and osmotic stress, but increased resistance to ABA inhibition. Overexpression of MtHHO3 in M. truncatula resulted in decreased tolerance of salinity, while loss-of-function mutants mthho3-1 and mthho3-2 were more resistant to salt stress compared with wild-type plants. qRT-PCR analyses showed that MtHHO3 downregulated the expression of genes in stress and ABA responsive pathways. We further demonstrated that MtHHO3 repressed the transcription of the pathogenesis-related gene MtPR2 by binding to its promoter. Overall, these results indicate that MtHHO3 negatively regulates salt stress response in plants and deepen our understanding of the role of the GARP subfamily transcription factors in modulating salt stress and ABA signaling.

Identification of Salt-Sensitive and Salt-Tolerant Genes through Weighted Gene Co-Expression Networks across Multiple Datasets: A Centralization and Differential Correlation Analysis.

Salt stress is a significant challenge that severely hampers rice growth, resulting in decreased yield and productivity. Over the years, researchers have identified biomarkers associated with salt stress to enhance rice tolerance. However, the understanding of the mechanism underlying salt tolerance in rice remains incomplete due to the involvement of multiple genes. Given the vast amount of genomics and transcriptomics data available today, it is crucial to integrate diverse datasets to identify key genes that play essential roles during salt stress in rice. In this study, we propose an integration of multiple datasets to identify potential key transcription factors. This involves utilizing network analysis based on weighted co-expression networks, focusing on gene-centric measurement and differential co-expression relationships among genes. Consequently, our analysis reveals 86 genes located in markers from previous meta-QTL analysis. Moreover, six transcription factors, namely LOC_Os03g45410 (OsTBP2), LOC_Os07g42400 (OsGATA23), LOC_Os01g13030 (OsIAA3), LOC_Os05g34050 (OsbZIP39), LOC_Os09g29930 (OsBIM1), and LOC_Os10g10990 (transcription initiation factor IIF), exhibited significantly altered co-expression relationships between salt-sensitive and salt-tolerant rice networks. These identified genes hold potential as crucial references for further investigation into the functions of salt stress response in rice plants and could be utilized in the development of salt-resistant rice cultivars. Overall, our findings shed light on the complex genetic regulation underlying salt tolerance in rice and contribute to the broader understanding of rice's response to salt stress.

GhWRKY4 binds to the histone deacetylase GhHDA8 promoter to regulate drought and salt tolerance in Gossypium hirsutum

Soil drought and salinization, caused by water deficiency, have become the greatest concerns limiting crop production. Up to now, the WRKY transcription factor and histone deacetylase have been shown to be involved in drought and salt responses. However, the molecular mechanism underlying their interaction remains unclear in cotton. Herein, we identified GhWRKY4, a member of WRKY gene family, which is induced by drought and salt stress and is located in the nucleus. The ectopic expression of GhWRKY4 in Arabidopsis enhanced drought and salt tolerance, and suppressing GhWRKY4 in cotton increased susceptibility to drought and salinity. Subsequently, DAP-seq analysis revealed that the W box element in the promoter of stress-induced genes could potentially be the binding target for GhWRKY4 protein. GhWRKY4 binds to the promoters of GhHDA8 and GhNHX7 via W box element, and the expression level of GhHDA8 was increased in GhWRKY4-silenced plants. In addition, GhHDA8-overexpressed Arabidopsis were found to be hypersensitive to drought and salt stress, while silencing of GhHDA8 enhanced drought and salt tolerance in cotton. The stress-related genes, such as GhDREB2A, GhRD22, GhP5CS, and GhNHX7, were induced in GhHDA8-silenced plants. Our findings indicate that the GhWRKY4-GhHDA8 module regulates drought and salt tolerance in cotton. Collectively, the results provide new insights into the coordination of transcription factors and histone deacetylases in regulating drought and salt stress responses in plants.

Optimization of preparation and transformation of protoplasts from Populus simonii × P. nigra leaves and subcellular localization of the major latex protein 328 (MLP328)

BackgroundPopulus simonii × P. nigra is an ideal material for studying the molecular mechanisms of woody plants. In recent years, research on Populus simonii × P. nigra has increasingly focused on the application of transgenic technology to improve salt tolerance. However, the rapid characterization of gene functions has been hampered by the long growth cycle and exceedingly poor transformation efficiency. Protoplasts are an important tool for plant gene engineering, which can assist with challenging genetic transformation and the protracted growth cycle of Populus simonii × P. nigra. This study established an optimized system for the preparation and transformation of protoplasts from Populus simonii × P. nigra leaves, making genetic research on Populus simonii × P. nigra faster and more convenient. Major Latex Protein (MLP) family genes play a crucial role in plant salt stress response. In the previous study, we discovered that PsnMLP328 can be induced by salt treatment, which suggested that this gene may be involved in response to salt stress. Protein localization is a suggestion for its function. Therefore, we conducted subcellular localization analysis using protoplasts of Populus simonii × P. nigra to study the function of the PsnMLP328 gene preliminarily.ResultsThis study established an optimized system for the preparation and transformation of Populus simonii × P. nigra protoplasts. The research results indicate that the optimal separation scheme for the protoplasts of Populus simonii × P. nigra leaves included 2.5% cellulase R-10, 0.6% macerozyme R-10, 0.3% pectolyase Y-23, and 0.8 M mannitol. After enzymatic digestion for 5 h, the yield of obtained protoplasts could reach up to 2 × 107 protoplasts/gFW, with a high viability of 98%. We carried out the subcellular localization analysis based on the optimized transient transformation system, and the results indicated that the MLP328 protein is localized in the nucleus and cytoplasm; thereby proving the effectiveness of the transformation system.ConclusionIn summary, this study successfully established an efficient system for preparing and transforming leaf protoplasts of Populus simonii × P. nigra, laying the foundation for future research on gene function and expression of Populus simonii × P. nigra.

Comparative Transcript Profiling and Multiplex qRT-PCR Analysis Between Salt-Tolerant and Sensitive Wheat Genotypes

Identification of candidate genes combined with gene expression profiling carries importance to facilitate the molecular basis of salt stress response in plants. Here, cDNA-AFLP was used to compare the transcribed sequences among two bread and two durum wheat genotypes with different levels of salt tolerance. Transcript derived fragments (TDFs) screened on polyacrylamide gels and 36 salt stress induced unique fragments were detected in salt tolerant bread wheat genotype (Alpu cv.). The fragment size of these 36 TDFs was ranged between 99bp to 252bp. Full sequence information of 14 TDFs were obtained after cloning, then GeXP analyzer-based multiplex qRT-PCR assay was performed on leaf tissue derived from 12 TDFs. Targeted gene expression levels of two TDFs (TDF4-GT066302 and TDF11-GT066301) were showed clear upregulation in salt tolerant bread wheat genotype (Alpu cv.) and they were matched with hypothetical proteins. Especially, gene expression level of GT066301 was increased as 3.28 fold at 27th hours of salt stress for salt tolerant genotype. According to blastx similarity results, out of 14 sequenced fragments, two TDFs were closely matched with “cytochrome P450 monooxygenase” protein while four of them matched with Oryza “hypothetical” and “unknown” proteins. Outputs of this study might ensure comparative data for hypothetical protein gene expression and new useful alleles in response to salt stress in wheat.

In-silico identification and characterization of sucrose transporter genes and their differential expression pattern under salinity stress in Glycine max

Plant sucrose transporters, involved in sugar transport, are key in facilitating sugar flux across the plant cell membranes. However, external stress stimuli significantly impact these sucrose transporters (SWEET/MST/SUT) and, ultimately, the distribution of photosynthates. This has importance as sucrose is a prime energy source, a signaling molecule, and an osmolyte playing a key role in growth and development processes. This study aims to identify and comprehensive in silico characterization and involvement of soybean sucrose transporters GlymaSWEET, GlymaMST, and GlymaSUT in plant development and salt stress responses in an important oilseed crop soybean (Glycine max L.). A genome-wide screening of soybean revealed 13 GlymaSWEET, 6 GlymaMST, and 5 GlymaSUT orthologues as confirmed from the eggNOG database. Probable sites of these proteins were found to be the membranes of cells and organelles, as suggested by their sub-cellular localization. The cis-regulatory elements of these transporters’ promoters indicated their involvement in environmental stress responses. MicroRNA interactions with these transporters were also studied, besides 3-D protein structure prediction using in silico approaches. To gain an insight into the functional divergence of GlymaSWEET, GlymaMST, and GlymaSUT transporters, qRT-PCR-based gene expression analysis was done both in control and salt-treated root and leaf tissues of two contrasting Indian soybean varieties MAUS-47 (salt-tolerant) and Gujosoya-2 (salt-sensitive). Differential gene expression was observed with varying degrees amongst the varieties and the treatments. Overall, we can conclude that the identified GlymaSWEET, GlymaMST, and GlymaSUT have the potential to be explored as candidate genes for engineering salinity stress tolerance in soybean and other plants.

Epigenetic regulation in plant salt stress response

As sessile organisms, plants have evolved sophisticated regulatory systems because they must respond to a variety of environmental stimuli. Salt stress, in particular, affects the growth of crop plants and limits crop yield in many saline regions around the world. Therefore, developing salt-tolerant crop cultivars has great significance in global food security. Epigenetic regulation, which contributes to phenotype plasticity without altering the genotype, have important roles in how plant respond to salt stress. Moreover, the heritable nature of epigenetic modifications makes it possible to maintain the information and pass it down to the next generation as stress memory, thus enables the plant and its progeny to cope with recuring stress more efficiently. This paper provides an overview of major achievements in this field by analyzing previous studies, and concludes that major epigenetic regulatory pathways, including histone modifications, DNA modifications and small RNAs, are essential in plant salt stress response, and further insights into these mechanisms are of great value.

A DEAD box helicase Psp68 positively regulates salt stress responses in marker-free transgenic rice plants.

Helicases are the motor proteins not only involved in transcriptional and post-transcription process but also provide abiotic stress tolerance in many crops. The p68, belong to the SF2 (DEAD-box helicase) family proteins and overexpression of Psp68 providing enhanced tolerance to transgenic rice plants. In this study, salinity tolerant marker-free transgenic rice has been developed by overexpressing Psp68 gene and phenotypically characterized. The Psp68 overexpressing marker-free transgenic rice plants were initially screened in the rooting medium containing salt stress and 20% polyethylene glycol (PEG). Stable integration and overexpression of Psp68 in marker-free transgenic lines were confirmed by molecular analyses including PCR, southern, western blot, and qRT-PCR analyses. The marker-free transgenic lines showed enhanced tolerance to salinity stress as displayed by early seed germination, higher chlorophyll content, reduced necrosis, more survival rate, improved seedling growth and more grain yield per plant. Furthermore, Psp68 overexpressing marker-free transgenics also accumulated less Na+ and higher K+ ions in the presence of salinity stress. Phenotypic analyses also revealed that marker-free transgenic rice lines efficiently scavenge ROS-mediated damages as displayed by lower H2O2 and malondialdehyde content, delayed electrolyte leakage, higher photosynthetic efficiency, membrane stability, proline content and enhanced activities of antioxidants enzymes. Overall, our results confirmed that Psp68 overexpression confers salinity stress tolerance in marker-free transgenics, hence the technique could be utilized to develop genetically modified crops without any biosafety issues.

OsLPR5 Encoding Ferroxidase Positively Regulates the Tolerance to Salt Stress in Rice.

Salinity is a major abiotic stress that harms rice growth and productivity. Low phosphate roots (LPRs) play a central role in Pi deficiency-mediated inhibition of primary root growth and have ferroxidase activity. However, the function of LPRs in salt stress response and tolerance in plants remains largely unknown. Here, we reported that the OsLPR5 was induced by NaCl stress and positively regulates the tolerance to salt stress in rice. Under NaCl stress, overexpression of OsLPR5 led to increased ferroxidase activity, more green leaves, higher levels of chlorophyll and lower MDA contents compared with the WT. In addition, OsLPR5 could promote the accumulation of cell osmotic adjustment substances and promote ROS-scavenging enzyme activities. Conversely, the mutant lpr5 had a lower ferroxidase activity and suffered severe damage under salt stress. Moreover, knock out of OsLPR5 caused excessive Na+ levels and Na+/K+ ratios. Taken together, our results exemplify a new molecular link between ferroxidase and salt stress tolerance in rice.

Transcriptome-Based Comparative Analysis of Transcription Factors in Response to NaCl, NaOH, and Na2CO3 Stresses in Roots of Autotetraploid Rice (Oryza sativa L.)

Soil salinity is a severe constraint on crop productivity that triggers plant salt stress response pathways. The salt stress responses are controlled by transcriptional regulatory networks that enhance plant stress tolerance by manipulating the expression of transcription factor (TFs)-encoding genes. Identifying TFs associated with salt tolerance contributes to salt-tolerant crop breeding. In this study, a comparative transcriptome analysis was performed to investigate the global gene expression of entire TFs in diploid and autotetraploid rice with different salt tolerance levels, considering NaCl stress, NaOH stress, and Na2CO3 stress. A total of 54, 54 and 55 TF families were co-expressed in diploid and tetraploid roots under three stresses, respectively. Furthermore, we investigated differentially expressed TFs (DE-TFs) based on different comparisons, and the statistical analysis indicated that the DE-TFs derived from the three types of stress were as follows: Na2CO3 (53 TF families, 1356 DE-TFs) > NaCl (19 TF families, 214 DE-TFs) > NaOH (18 TF families, 152 DE-TFs). These results imply that Na2CO3 stress induced a more obvious biological responses in the roots than the other two stresses. GO and KEGG pathway enrichment analysis of DE-TFs revealed the importance of plant hormone signal transduction and MAPK signaling pathways that may contribute to the saline–alkaline tolerance of tetraploid rice. This study provides gene resources that are valuable for exploring the regulatory mechanism of TFs involved in the saline–alkaline tolerance of polyploid rice.

Different salt stress response in Kalanchoe plants during vegetative and asexual propagation

Different salt stress response in Kalanchoe plants during vegetative and asexual propagation

The Sm core protein SmEb regulates salt stress responses through maintaining proper splicing of RCD1 pre-mRNA in Arabidopsis.

Salt stress adversely impacts crop production. Several spliceosome components have been implicated in regulating salt stress responses in plants, however, the underlying molecular basis is still unclear. Here we report that the spliceosomal core protein SmEb is essential to salt tolerance in Arabidopsis. Transcriptome analysis showed that SmEb modulates alternative splicing of hundreds of pre-mRNAs in plant response to salt stress. Further study revealed that SmEb is crucial in maintaining proper ratio of two RCD1 splicing variants (RCD1.1/RCD1.2) important for salt stress response. In addition, RCD1.1 but not RCD1.2 is able to interact with the stress regulators and attenuates salt-sensitivity by decreasing salt-induced cell death in smeb-1 mutant. Together, our findings uncovered the essential role of SmEb in the regulation of alternative pre-mRNA splicing in salt stress response.

Effect of ACC oxidase gene AhACOs on salt tolerance of peanut

ACC oxidase (ACO) is one of the key enzymes that catalyze the synthesis of ethylene. Ethylene is involved in salt stress response in plants, and salt stress seriously affects the yield of peanut. In this study, AhACO genes were cloned and their functions were investigated with the aim to explore the biological function of AhACOs in salt stress response, and to provide genetic resources for the breeding of salt-tolerant varieties of peanut. AhACO1 and AhACO2 were amplified from the cDNA of salt-tolerant peanut mutant M29, respectively, and cloned into the plant expression vector pCAMBIA super1300. The recombinant plasmid was transformed into Huayu22 by pollen tube injection mediated by Agrobacterium tumefaciens. After harvest, the small slice cotyledon was separated from the kernel, and the positive seeds were screened by PCR. The expression of AhACO genes was analyzed by qRT-PCR, and the ethylene release was detected by capillary column gas chromatography. Transgenic seeds were sowed and then irrigated with NaCl solution, and the phenotypic changes of 21-day-seedings were recorded. The results showed that the growth of transgenic plants were better than that of the control group Huayu 22 upon salt stress, and the relative content of chlorophyll SPAD value and net photosynthetic rate (Pn) of transgenic peanuts were higher than those of the control group. In addition, the ethylene production of AhACO1 and AhACO2 transgenic plants were 2.79 and 1.87 times higher than that of control peanut, respectively. These results showed that AhACO1 and AhACO2 could significantly improve the salt stress tolerance of transgenic peanut.

Analysis of the chloroplast crotonylome of wheat seedling leaves reveals the roles of crotonylated proteins involved in salt-stress responses.

Lysine crotonylation (Kcr) is a novel post-translational modification and its function in plant salt-stress responses remains unclear. In this study, we performed the first comprehensive chloroplast crotonylome analysis of wheat seedling leaves to examine the potential functions of Kcr proteins in salt-stress responses. In a total of 471 chloroplast proteins, 1290 Kcr sites were identified as significantly regulated by salt stress, and the Kcr proteins were mainly involved in photosynthesis, protein folding, and ATP synthesis. The identified Kcr sites that responded to salt stress were concentrated within KcrK and KcrF motifs, with the conserved KcrF motif being identified in the Kcr proteins of wheat chloroplasts for the first time. Notably, 10 Kcr sites were identified in fructose-1,6-bisphosphate aldolase (TaFBA6), a key chloroplast metabolic enzyme involved in the Calvin-Benson cycle. Site-directed mutagenesis of TaFBA6 showed that the Kcr at K367 is critical in maintaining its enzymatic activity and in conferring salt tolerance in yeast. Further molecular dynamic simulations and analyses of surface electrostatic potential indicated that the Kcr at K367 could improve the structural stability of TaFBA6 by decreasing the distribution of positive charges on the protein surface to resist alkaline environments, thereby promoting both the activity of TaFBA6 and salt tolerance.

MicroRNA4359b positively regulates the soybean response to salt stress by targeting the F-box protein GmFBX193

MicroRNAs (miRNAs) have important functions in the plant salt stress response. However, the functions of nonconserved miRNAs in soybean salt stress adaptation remain unclear. In this study, the soybean nonconserved miRNA gma-miR4359b and its target mRNA F-box gene GmFBX193 were functionally identified in response to salt stress. gma-miR4359b responded to salt stress in soybean hairy roots, stems, and leaves. Under salt stress, the root length ratio, root surface area ratio, root volume ratio, root tip number, survival rate, chlorophyll content, soluble sugar content, proline content, superoxide dismutase activity, and peroxidase enzyme activity of soybean hairy roots overexpressing gma-miR4359b (MIR4359b) were increased compared to those of the K599 (control) soybean hairy roots, while the relative electrolyte leakage and malondialdehyde content of the MIR4359b soybean hairy roots decreased. In contrast, soybean hairy roots in which target mimicry (MIM4359b) and short tandem target mimic (STTM4359b) inhibited gma-miR4359b exhibited a salt-sensitive phenotype. The transcription level of GmFBX193 was decreased in MIR4359b soybean hairy roots, while the transcription level of GmFBX193 was increased in MIM4359b and STTM4359b soybean hairy roots. GmFBX193 responded to salt stress in soybean roots, and GmFBX193 was identified as a nuclear-localized protein. Under salt stress, soybean hairy roots overexpressing GmFBX193 had a similar phenotype to MIM4359b and STTM4359b soybean hairy roots. Compared with K599 (control) soybean hairy roots, MIR4359b soybean hairy roots had 172 differentially expressed genes (DEGs), and MIM4359b soybean hairy roots had 2129 DEGs. Some known stress-related transcription factors were included among the DEGs. Taken together, these results suggest that gma-miR4359b plays a positive role in the soybean salt stress response by negatively regulating GmFBX193.

Mild and severe salt stress responses are age-dependently regulated by abscisic acid in tomato.

Salt stress hampers plant growth and development through both osmotic and ionic imbalances. One of the key players in modulating physiological responses towards salinity is the plant hormone abscisic acid (ABA). How plants cope with salinity largely depends on the magnitude of the soil salt content (stress severity), but also on age-related developmental processes (ontogeny). Here we studied how ABA directs salt stress responses in tomato plants for both mild and severe salt stress in leaves of different ages. We used the ABA-deficient mutant notabilis, which contains a null-mutation in the gene of a rate-limiting ABA biosynthesis enzyme 9-cis-epoxycarotenoid dioxygenase (NCED1), leading to impaired stomatal closure. We showed that both old and young leaves of notabilis plants keep a steady-state transpiration and photosynthesis rate during salt stress, probably due to their dysfunctional stomatal closure. At the whole plant level, transpiration declined similar to the wild-type, impacting final growth. Notabilis leaves were able to produce osmolytes and accumulate ions in a similar way as wild-type plants, but accumulated more proline, indicating that osmotic responses were not impaired by the NCED1 mutation. Besides NCED1, also NCED2 and NCED6 are strongly upregulated under salt stress, which could explain why the notabilis mutant did not show a lower ABA content upon salt stress, except in young leaves. This might be indicative of a salt-mediated feedback mechanism on NCED2/6 in notabilis and might explain why notabilis plants seem to perform better under salt stress compared to wild-type plants with respect to biomass and water content accumulation.

Transcription factors ZmNF-YA1 and ZmNF-YB16 regulate plant growth and drought tolerance in maize.

The identification of drought stress regulatory genes is crucial for the genetic improvement of maize (Zea mays L.) yield. Nuclear factors Y (NF-Ys) are important transcription factors, but their roles in the drought stress tolerance of plants and underlying molecular mechanisms are largely unknown. In this work, we used yeast two-hybrid screening to identify potential interactors of ZmNF-YB16 and confirmed the interaction between ZmNF-YA1 and ZmNF-YB16-YC17 and between ZmNF-YA7 and ZmNF-YB16-YC17. ZmNF-YB16 interacted with ZmNF-YC17 via its histone fold domain to form a heterodimer in the cytoplasm and then entered the nucleus to form a heterotrimer with ZmNF-YA1 or ZmNF-YA7 under osmotic stress. Overexpression of ZmNF-YA1 improved drought and salt stress tolerance and root development of maize, whereas zmnf-ya1 mutants exhibited drought and salt stress sensitivity. ZmNF-YA1-mediated transcriptional regulation, especially in JA signaling, histone modification, and chromatin remodeling, could underlie the altered stress tolerance of zmnf-ya1 mutant plants. ZmNF-YA1 bound to promoter CCAAT motifs and directly regulated the expression of multiple genes that play important roles in stress responses and plant development. Comparison of ZmNF-YB16- and ZmNF-YA1-regulated genes showed that ZmNF-YA1 and ZmNF-YB16 have similar biological functions in stress responses but varied functions in other biological processes. Taken together, ZmNF-YA1 is a positive regulator of plant drought and salt stress responses and is involved in the root development of maize, and ZmNF-Y complexes with different subunits may have discrepant functions.