狗牙根是全球应用最广、抗旱性最强的暖季型草种之一，揭示狗牙根抗旱机制，有重要科学意义和潜在应用价值，但目前对狗牙根抗旱分子机理所知很少。环类固醇甲基转移酶1（SMT1）是植物甾醇合成途径的第一个关键酶，其基因表达下调后导致胆固醇积累，但胆固醇的植物生理作用并不清楚。前一个基金课题取得了突破性进展，初步揭示SMT1下调导致胆固醇积累，从而调节MYB59、SAMDC等系列基因表达，是狗牙根突变体表现出矮化和抗旱的原因。在此基础上，本项目拟重点围绕狗牙根MYB59开展深入研究，获得上调和下调MYB59的转基因植物，阐明MYB59及其调控的下游基因与抗旱性的关系、MYB59是否为胆固醇提高抗旱性所必需；以酵母单杂实验证明MYB59与其调控的下游基因启动子的互作关系，比较SMT1、胆固醇和MYB59调控的基因表达谱及代谢途径的异同，从而揭示SMT1负调控狗牙根抗旱性的的分子机制和胆固醇的生理功能。

Bermudagrass is one of the most widely used turfgrass species with drought tolerance. It is important to understand the mechanism of drought tolerance in bermudagrass, while little is known at molecular levels. Sterol methyltransferase 1 (SMT1) is the first key enzyme in phytosterol synthesis. Down-regulation of SMT1 gene expression leads to accumulation of cholesterol. However, the physiological role of cholesterol in plants is unknown. In our previous studies supported by NSFC, it has been revealed that dwarfism phenotype with elevated drought tolerance in a bermudagrass mutant was associated with down-regulated SMT1 expression, as a result, cholesterol was accumulated, which in turn induced expression of lots of genes including MYB59 transcription factor and S-adenosylmethionine decarboxylase gene. On the basis of the above progress, this project continues investigations on regulation of SMT1 and cholesterol on drought tolerance in bermudagrass through analysis of MYB59 function, for understanding of the physiological role of cholesterol and how SMT1 negatively regulate drought tolerance. Transgenic bermudagrass plants overexpressing and down-regulating MYB59 expression by RNAi will be generated, followed by analysis of drought tolerance, transcript profiles, and response to cholesterol in transgenic plants in comparison to the wild type. In addition, interactions of MYB59 with the promoters of its downstream gene(s) will be tested by using yeast one hybrid system and electrophoretic mobility shift assay. Transcriptome and metabolites in the above transgenic plants as compared with the wild type will also be examined in the project to reveal the processes regulated by SMT1, cholesterol, and MYB59.