水稻对白叶枯的感病基因多态性以及功能分析

Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is a devastating disease of many rice varieties causing huge economic losses. TAL (Transcriptional activator-like) effectors, which are secreted and translocated by Type III secretion system, are the major pathogenicity determinant of Xoo in inducing BB. TAL effectors specifically target and activate rice genes to promote disease development, which are also termed as susceptibility genes. In rice, multiple TAL effector target genes that contribute the susceptibility belong to MtN3/SWEET gene family. Five susceptibility genes in SWEET family that recognized by known or unknown TAL effectors have been reported. The sequence mutations, deletions or insertions in target gene EBE（Effector Binding Elements）region could reduce binding and activation activities, thus affect or even abolish the disease symptom. Our hypotheses are that the EBE sequence variations in SWEET genes will have a significant impact on the genes activation as well as the disease happening, and the resistance phenotype of some rice cultivars in response to specific Xoo strains is account for sequence changes in the EBE regions. In this proposed studies, we aim to detect the EBE sequence polymorphism of the five SWEET susceptibility gene between diverse rice accessions or landraces. This proposal will also statistically investigate the relationship between EBE sequences in SWEET gene promoters and gene activations or rice reactions in response to Xoo strains that contain the corresponding TAL effectors. In addition, we will also evaluate the susceptibility contributions to BB of some new SWEET genes from other rice varieties. The proposed research offers an opportunity to develop an extensive understanding of the roles of SWEET genes from diverse rice varieties in susceptibility to BB, and also will help to identify new resistance gene alleles.

由黄单胞杆菌Xanthomonas oryzae pv. oryzae (Xoo)所导致的水稻细菌性白叶枯病是水稻上非常严重的病害，它能造成巨大的产量损失。Xoo中由三型分泌系统转运的TAL效应因子是诱导白叶枯的重要因素，它们能够特异性地结合并且激活水稻基因的表达并促进病害的发生，这些基因也被称作感病基因。在水稻中，至少5个TAL效应因子靶标感病基因都属于MtN3/SWEET基因家族，而已经发现有5个SWEET基因是针对白叶枯的感病基因。TAL效应因子结合序列（EBE）的突变会减少结合和激活活性，并且影响病害的症状程度。我们预测5个SWEET基因启动子上潜在EBE序列的变化会对基因的激活表达和病害发生有很大的影响，某些对Xoo有抗性的品种也可能是由于在特定EBE序列上的改变。本项目目标是探索不同水稻种质中已知的5个SWEET感病基因在EBE序列上的多态性。此项目也将会在统计学角度阐述SWEET基因上EBE的序列和这些基因受相关TAL效应因子的激活情况以及水稻对含有相关TAL效应因子的Xoo菌株反应之间的关系。我们也将评估其他水稻品种中一些新的SWEET基因对感病的贡献程度。