钙调素结合转录因子AtSR1调控低磷胁迫响应的分子机制研究

Phosphorus is one of the major plant nutrients. Low availability of phosphate (Pi) in soil has become a major constraint for plant growth and productivity. Phosphate deficiency has forced the plants to evolve a large number of adaptations, and these adaptations are regulated by a delicate molecular mechanism which is mainly controlled at the transcriptional level. During our preliminary study, AtSR1, encoding for a calmodulin-binding transcription activator factor, was identified to be induced by phosphate starvation. Transgenic plants overexpressing AtSR1 showed improved tolerance to low phosphate stress, and vice versa for Atsr1 null mutant. Using bioinformatics and biochemistry methods, we have identified AtAST1 (Arabidopsis thaliana AtSR1 Target1), a homolog of phosphate translocator PHO1, as a putative downstream target gene of AtSR1. The following research aspects will be performed in this work: functional analysis of AtAST1 in null mutant and over expression lines, expression profiles analysis in various organs, EMSA and ChIP assays analysis and epistasis analysis. The expected results will help elucidate the mechanism by which AtSR1 regulates plant responses to low phosphate stress and add to the knowledge base for molecular breeding of crops with improved tolerance to low phosphate environments.

磷是植物必须的大量元素。土壤有效磷的不足使植物遭受低磷胁迫，影响植物生长发育。植物响应低磷胁迫的分子机制中，基因转录水平的表达调控起重要作用。本研究发现钙调素结合转录因子基因AtSR1表达受低磷胁迫诱导，Atsr1缺失突变体对低磷胁迫敏感，过量表达AtSR1增强转基因株系对低磷胁迫的耐受性。通过生物信息学与生化分析相结合的方法筛选到AtSR1可能调控的下游靶基因AtAST1(Arabidopsis thaliana AtSR1 Target1)，该基因是磷转运基因PHO1的同源基因。本项目拟通过过量表达株系与缺失突变体低磷表型分析、组织器官表达模式分析、EMSA和免疫共沉淀分析以及基因上位性分析，对AtSR1调控AtAST1的表达开展研究。本项目的开展将阐明AtSR1参与植物低磷胁迫响应的作用机制，对培育磷高效利用作物新品种具有重要的理论和应用价值。

磷是植物必须的大量元素。本项目主要研究AtSR1通过调控AtAST1基因的表达调节拟南芥对磷的吸收转运。项目主要研究成果如下：①AtSR1基因的表达受到低磷胁迫诱导表达。相比Atsr1功能缺失突变体，过表达AtSR1的转基因植株增强对低磷胁迫的耐受性，茎部积累更高含量的磷酸盐。②q-RT PCR分析显示部分磷胁迫响应基因 (PHT1:1、PHT1:4、AtIPS1、AT4、GAPC1、AtCP5、PHO1) 在Atsr1突变体中的表达被抑制。③利用在Atsr1突变体背景下回补不同钙调素结合能力I909V (cM1)，K907E (cM2)和∆CaMBD(cM3)的AtSR1蛋白，不同遗传材料在花青素含量和磷酸盐含量水平上无明显差异，表明AtSR1可能并不直接通过与钙调素的结合来参与磷胁迫信号转导。④Atast1突变体对缺磷敏感，利用AST1启动子和其ORF片段构建的功能回补植株能恢复Atast1磷敏感表型；GUS染色显示AtAST1主要在根和茎叶的中柱细胞中表达。⑤Atsr1突变体中AtAST1的表达被抑制，免疫共沉淀和凝胶阻滞试验表明AtSR1蛋白能够结合到AtAST1启动子区域中的CGCG-box元件，表明AtSR1能直接调控AtAST1的表达。