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Calmodulin, a highly conserved calcium-binding protein, plays a crucial role in response to salt stress. Previous studies investigated sequence and function of calmodulin members in some plants, but their roles in rice have not been fully elucidated. Three OsCaM1 genes namely OsCaM1-1/2/3 encode the same OsCaM1 protein. Here, we found that OsCaM1-1 had significantly higher expression than the other two genes under salt stress. After 4 weeks of exposure to 75 mM NaCl, OsCaM1-1 overexpressed mutants showed higher salt tolerance, while knocked-out mutants exhibited lower salt tolerance, compared to the wild type. Moreover, the oscam1-1 mutants had higher Na + concentration and Na + /K + ratio in both shoots and roots, less instantaneous K + and Ca 2+ fluxes in roots, compared to wild type under salt stress, indicating the involvement of OsCaM1-1 in regulation of Na + and K + homoeostasis via Ca 2+ signal. RNA-seq analysis identified 452 differentially expressed genes (DEGs) regulated by OsCaM1-1 and salt stress, and they were mainly enriched in nucleus DNA-binding activities, including ABI5, WRKY76, WRKY48 and bHLH120 transcription factors. Knockout of OsCaM1-1 also modulated the expression of Na + transporters, including HKT1;1, HKT1;5, SOS1, NHX1 and NHX4. In conclusion, OsCaM1-1 positively regulates salt tolerance in rice through mediating ion homoeostasis., (© 2024 John Wiley & Sons Ltd.)

The roles of clock components in salt stress tolerance remain incompletely characterized in rice. Here, we show that, among OsPRR (Oryza sativa Pseudo-Response Regulator) family members, OsPRR73 specifically confers salt tolerance in rice. Notably, the grain size and yield of osprr73 null mutants were significantly decreased in the presence of salt stress, with accumulated higher level of reactive oxygen species and sodium ions. RNA sequencing and biochemical assays identified OsHKT2;1, encoding a plasma membrane-localized Na + transporter, as a transcriptional target of OsPRR73 in mediating salt tolerance. Correspondingly, null mutants of OsHKT2;1 displayed an increased tolerance to salt stress. Immunoprecipitation-mass spectrometry (IP-MS) assays further identified HDAC10 as nuclear interactor of OsPRR73 and co-repressor of OsHKT2;1. Consistently, H3K9ac histone marks at OsHKT2;1 promoter regions were significantly reduced in osprr73 mutant. Together, our findings reveal that salt-induced OsPRR73 expression confers salt tolerance by recruiting HDAC10 to transcriptionally repress OsHKT2;1, thus reducing cellular Na + accumulation. This exemplifies a new molecular link between clock components and salt stress tolerance in rice., (© 2020 The Authors. Published under the terms of the CC BY NC ND 4.0 license.)

Calmodulin, a highly conserved calcium‐binding protein, plays a crucial role in response to salt stress. Previous studies investigated sequence and function of calmodulin members in some plants, but their roles in rice have not been fully elucidated. Three OsCaM1 genes namely OsCaM1‐1/2/3 encode the same OsCaM1 protein. Here, we found that OsCaM1‐1 had significantly higher expression than the other two genes under salt stress. After 4 weeks of exposure to 75 mM NaCl, OsCaM1‐1 overexpressed mutants showed higher salt tolerance, while knocked‐out mutants exhibited lower salt tolerance, compared to the wild type. Moreover, the oscam1‐1 mutants had higher Na+ concentration and Na+/K+ ratio in both shoots and roots, less instantaneous K+ and Ca2+ fluxes in roots, compared to wild type under salt stress, indicating the involvement of OsCaM1‐1 in regulation of Na+ and K+ homoeostasis via Ca2+ signal. RNA‐seq analysis identified 452 differentially expressed genes (DEGs) regulated by OsCaM1‐1 and salt stress, and they were mainly enriched in nucleus DNA‐binding activities, including ABI5, WRKY76, WRKY48 and bHLH120 transcription factors. Knockout of OsCaM1‐1 also modulated the expression of Na+ transporters, including HKT1;1, HKT1;5, SOS1, NHX1 and NHX4. In conclusion, OsCaM1‐1 positively regulates salt tolerance in rice through mediating ion homoeostasis. Summary statement: Calmodulin plays a crucial role in response to salt stress. Knockout of OsCaM1‐1 modulated the expressions of HKT1;5, HKT1;1, NHX1 and SOS1, highlighting the positive role of OsCaM1‐1 in the regulation of salt tolerance in rice through mediating ion homoeostasis. [ABSTRACT FROM AUTHOR]

A plant's ability to cope with salt stress is highly correlated with their ability to reduce the accumulation of sodium ions in the shoot. Arabidopsis mutants affected in the ABSCISIC ACID INSENSITIVE ( ABI) 4 gene display increased salt tolerance, whereas ABI4-overexpressors are hypersensitive to salinity from seed germination to late vegetative developmental stages. In this study we demonstrate that abi4 mutant plants accumulate lower levels of sodium ions and higher levels of proline than wild-type plants following salt stress. We show higher HKT1;1 expression in abi4 mutant plants and lower levels of expression in ABI4-overexpressing plants, resulting in reduced accumulation of sodium ions in the shoot of abi4 mutants. HKT1;1 encodes a sodium transporter which is known to unload sodium ions from the root xylem stream into the xylem parenchyma stele cells. We have shown recently that ABI4 is expressed in the root stele at various developmental stages and that it plays a key role in determining root architecture. Thus ABI4 and HKT1;1 are expressed in the same cells, which suggests the possibility of direct binding of ABI4 to the HKT1;1 promoter. In planta chromatin immunoprecipitation and in vitro electrophoresis mobility shift assays demonstrated that ABI4 binds two highly related sites within the HKT1;1 promoter. These sites, GC(C/G) GCTT(T), termed ABI4-binding element ( ABE), have also been identified in other ABI4-repressed genes. We therefore suggest that ABI4 is a major modulator of root development and function. [ABSTRACT FROM AUTHOR]