Histone deacetylase AtSRT2 regulates salt tolerance during seed germination via repression of vesicle-associated membrane protein 714 (VAMP714) in Arabidopsis.

Salt tolerance during seed germination is essential for seedling establishment under salt stress. Sirtuin-like proteins, NAD+ -dependent histone deacetylases, are involved in plant responses to abiotic stresses; however, the regulatory mechanism remains unknown. We elucidated the mechanism underlying AtSRT2 (a sirtuin-like protein)-mediated regulation of salt tolerance during seed germination in Arabidopsis. The AtSRT2 mutant srt2 exhibited significantly reduced seed germination percentages under salt stress; its targets were identified via chromatin immunoprecipitation coupled with ultra-high-throughput parallel DNA sequencing (ChIP-Seq) assay. Epistasis analysis was performed to identify AtSRT2-related pathways. Overexpression of SRT2.7, an AtSRT2 splice variant, rescued the salt-sensitive phenotype of mutant srt2. AtSRT2 histone deacetylation activity was important for salt tolerance during seed germination. The acetylation level of histone H4K8 locus in srt2-1 increased significantly under salt treatment. Vesicle-associated membrane protein 714 (VAMP714), a negative regulator of hydrogen peroxide (H2 O2 )-containing vesicle trafficking in cells, was identified as a target of AtSRT2. AtSRT2 regulated histone acetylation in the promoter region of VAMP714 and inhibited VAMP714 transcription under salt treatment. Seed germination percentage of double-mutant srt2-1vamp714 was close to that of single-mutant vamp714, and higher than that of single-mutant srt2 under salt stress. Hydrogen peroxide content and DNA damage increased after salt treatment in srt2 during seed germination. AtSRT2 regulates salt tolerance during seed germination through VAMP714 in Arabidopsis.

Foxtail millet MYB-like transcription factor SiMYB16 confers salt tolerance in transgenic rice by regulating phenylpropane pathway.

R2R3-MYB transcription factors play an important role in the synthesis of phenylpropanoid-derived compounds, which in turn provide salt tolerance in plant. In this study, we found that the expression of foxtail millet R2R3-MYB factor SiMYB16 can be induced by salt and drought. SiMYB16 is localized in the nucleus and acts as a transcriptional activator. Phylogenetic analysis indicates that SiMYB16 belongs to the R2R3-MYB transcription factor family subgroup 24. Transgenic rice expressing SiMYB16 (OX16) had a higher survival rate, lower malondialdehyde content, and heavier fresh weight compared with type (WT) under salt stress conditions. The transgenic plants also had a higher germination rate in salt treatment conditions and higher yield in the field compared with wild-type plants. Transcriptome analysis revealed that the up-regulated differential expression genes in the transgenic rice were mainly involved in phenylpropanoid biosynthesis, fatty acid elongation, phenylalanine metabolism, and flavonoid biosynthesis pathways. Quantitative real-time PCR analysis also showed that the genes encoding the major enzymes in the lignin and suberin biosynthesis pathways had higher expression level in SiMYB16 transgenic plants. Correspondingly, the content of flavonoid and lignin, and the activity of fatty acid synthase increased in SiMYB16 transgenic rice compared with wild-type plants under salt stress treatment. These results indicate that SiMYB16 gene can enhance plant salt tolerance by regulating the biosynthesis of lignin and suberin.

Overexpression of GmUBC9 Gene Enhances Plant Drought Resistance and Affects Flowering Time via Histone H2B Monoubiquitination.

Ubiquitylation is a form of post-translational modification of proteins that can alter localization, functionality, degradation, or transcriptional activity within a cell. E2 ubiquitin-conjugating enzyme (UBC) and E3 ubiquitin ligases are the primary determinants of substrate specificity in the context of ubiquitin conjugation. Multiubiquitination modifies target proteins for 26S proteasome degradation, while monoubiquitination controls protein activation and localization. At present, research on the monoubiquitination, especially histone monoubiquitination, has mostly focused on model plants with relatively few on crop species. In this study, we identified 91 UBC-like genes in soybean. The chromosomal localization, phylogenetic relationships, gene structures, and putative cis-acting elements were evaluated. Furthermore, the tissue-specific expression patterns of UBC Class I genes under drought stress were also investigated. Among Class I genes, GmUBC9 induction in response to drought stress was evident, and so this gene was selected for further analysis. GmUBC9 localized to the nucleus and endoplasmic reticulum. The overexpression of GmUBC9 in Arabidopsis led to enhanced tolerance for drought conditions across a range of stages of development, while overexpression in soybean hairy roots similarly led to improvements in tolerance for drought conditions, increased proline content, and reduced MDA content in soybean seedlings compared to wild type plants. HISTONE MONOUBIQUITINATION 2 (HUB2), an E3-like protein involved in histone H2B ubiquitylation (H2Bub1), was found to interact with GmUBC9 through Y2H analysis and BiFC assays in Arabidopsis and soybean. Under drought conditions, the level of H2Bub1 increased, and transcription of drought response genes was activated in GmUBC9 transgenic Arabidopsis and soybean. In addition, GmUBC9 transgenic Arabidopsis and soybean showed a late-flowering phenotype and had increased expression levels of the flowering related genes FLC and MAF4. These findings indicate that GmUBC9 is important for drought stress response and regulation of flowering time in soybean.