To isolate the genetic locus responsible for saline–alkaline stress tolerance, we developed a high-throughput activation tagging-based T-DNA insertion mutagenesis method using the model rice (Oryza sativa L.) variety Kitaake. One of the activation-tagged insertion lines, activation tagging 7 (AC7), showed increased tolerance to saline–alkaline stress. This phenotype resulted from the overexpression of a gene that encodes a SET DOMAIN GROUP 721 protein with H3K4 methyltransferase activity. Transgenic plants overexpressing OsSDG721 showed saline–alkaline stress-tolerant phenotypes, along with increased leaf angle, advanced heading and ripening dates. By contrast, ossdg721 loss-of-function mutants showed increased sensitivity to saline–alkaline stress characterized by decreased survival rates and reduction in plant height, grain size, grain weight and leaf angle. RNA sequencing (RNA-seq) analysis of wild-type Kitaake and ossdg721 mutants indicated that OsSDG721 positively regulates the expression level of HIGH-AFFINITY POTASSIUM (K⁺) TRANSPORTER1;5 (OsHKT1;5), which encodes a Na⁺-selective transporter that maintains K⁺/Na⁺ homeostasis under salt stress. Furthermore, we showed that OsSDG721 binds to and deposits the H3K4me3 mark in the promoter and coding region of OsHKT1;5, thereby upregulating OsHKT1;5 expression under saline–alkaline stress. Overall, by generating Kitaake activation-tagging pools, we established that the H3K4 methyltransferase OsSDG721 enhances saline–alkaline stress tolerance in rice.

中文翻译：

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SET DOMAIN GROUP 721 蛋白质在模型水稻品种 Kitaake 中的盐碱胁迫耐受性中发挥作用

为了分离导致盐碱胁迫耐受性的基因位点，我们开发了一种基于高通量激活标记的 T-DNA 插入诱变方法，使用模型水稻 ( Oryza sativa L.) 品种 Kitaake。激活标记的插入线之一，激活标记 7 ( AC7 )，显示出对盐碱胁迫的耐受性增加。这种表型是由编码具有 H3K4 甲基转移酶活性的 SET DOMAIN GROUP 721 蛋白的基因过表达引起的。过表达OsSDG721的转基因植物表现出耐盐碱胁迫表型，同时叶角增加、抽穗期和成熟期提前。相比之下，ossdg721功能丧失突变体对盐碱胁迫的敏感性增加，其特征是成活率降低，株高、粒大小、粒重和叶角降低。野生型 Kitaake 和ossdg721突变体的 RNA 测序 (RNA-seq) 分析表明，OsSDG721 正调节HIGH-AFFINITY POTASSIUM ( K ⁺ ) TRANSPORTER1;5 ( OsHKT1;5 ) 的表达水平，其编码 Na ⁺选择性转运蛋白在盐胁迫下维持 K ⁺ /Na ⁺稳态。此外，我们发现 OsSDG721 结合并沉积在 OsHKT1 的启动子和编码区中的 H3K4me3 标记；5，从而在盐碱胁迫下上调OsHKT1;5的表达。总体而言，通过生成 Kitaake 激活标记库，我们确定 H3K4 甲基转移酶 OsSDG721 增强了水稻对盐碱胁迫的耐受性。