极端天气如高温是造成粮食减产的主要因素之一，但目前植物耐高温的机制还很不清楚。前期工作中我们发现，水稻大粒基因BG3编码嘌呤通透酶，通过介导细胞分裂素转运调控水稻生长发育。BG3激活突变体bg3-D除籽粒增大外，耐高温能力显著增强。BG3L1为BG3同源基因，其过表达后表型却截然相反，籽粒变小，对高温超敏感。与BG3质膜定位不同，BG3L1定位于内质网上。实时定量PCR的结果显示BG3L1过表达植株地上部分的A类细胞分裂素应答因子的表达量显著下降。这些结果强烈暗示BG3和BG3L1作为同源蛋白通过共同调控细胞分裂素转运调节水稻耐高温。在此基础上，本项目拟对BG3和BG3L1相关水稻材料进行耐高温表型鉴定、细胞分裂素含量测定和处理、遗传杂交分析和RNA-seq分析，并分析细胞分裂素在耐高温中的作用，以解析BG3和BG3L1对耐高温的正反调控机制，为水稻耐高温育种改良提供理论支撑和基因资源。

Extreme weather, such as high temperature, is one of the main causes of grain yield reduction. However, the mechanism of high temperature tolerance in plants is still largely unclear. Our previous studies have found that big grain gene BG3, encoding a purine permease (PUP), regulate growth and development via modulating cytokinin transport in rice. In addition to enlarged grain size, bg3-D, the BG3 activated mutant, has significantly enhanced high temperature tolerance. However, overexpression of BG3-like1 (BG3L1), a homologous gene of BG3，led to reduced grain size and high sensitivity to high temperature. Unlike the location of BG3 on plasma membrane, BG3L1 was localized to the endoplasmic reticulum. Quantitative real time PCR (qRT-PCR) analysis indicated that expression of rice cytokinin type-A response regulator (OsRR) genes was significantly reduced in the shoots of the BG3L1 overexpression plants. These results strongly indicated that BG3 and BG3L1, as homologous proteins, regulate high temperature tolerance through co-controlling cytokinin transport in rice. Based on the previous results, in this proposed study, phenotype identification of high temperature tolerance, cytokinin content determination and treatment, genetic hybridization analysis, and RNA-seq analysis will be conducted on BG3- and BG3L1- related rice materials; the role of cytokinin in high temperature tolerance will be analyzed. Through these studies, we aim to elucidate the opposite regulation mechanisms of BG3 and BG3L1 on high temperature tolerance, and provide theoretical support and genetic resources for high temperature tolerance breeding of rice.