青枯菌Seppx05菌株能危害芝麻却不能侵染花生和辣椒的遗传学基础

Sesame is a characteristic crop planted in Jiangxi province. The sesame industry was damaged by bacterial wilt caused by Ralstonia solanacearum. Previous investigations have shown that most of R. solanacearum strains isolated from sesame, can infect peanuts, eggplants, tobaccos, tomatoes, potatoes and peppers as well, however the Seppx05 strain isolated from infected sesame in Poyang County of Jiangxi, can not infect both peanut and pepper. In this project, we attempt to elucidate the mechanism of host specify of the Seppx05 strain by combining the methods of comparative genomics, transgenic or gene knockout. The complete genome of the Seppx05 strain will be sequenced. The pathogenicity related genes especially T3SS effector genes, being deleted in Sepps05 strain or shared between Sepps05 strain and other strains will be screened. A series of mutant strains will be constructed by introducing the deleted genes into or knocking out the shared genes from the Seppx05 strain. The virulence capacity of these mutants will be evaluated on peanut, pepper and sesame. Simultaneously GFP-labeled strains of both wild-types and genetically modified strains will be used to monitor their colonization in the rhizospheres of peanut, pepper and sesame for elucidating the pathogenic function of these genes. The study would facilitate the understanding of the host specify mechanism of the Seppx05 strain, and help to make effective control strategies for this disease.

芝麻是江西特色优势产业作物，青枯病发生严重。前期研究发现，大多数芝麻青枯菌都能侵染茄子、烟草、番茄、马铃薯、辣椒和花生，而来自江西鄱阳县的芝麻菌株Seppx05能侵染茄子、烟草、番茄和马铃薯，却不能侵染花生和辣椒。因此，本项目拟测定Seppx05菌株的全基因组序列，采用比较基因组学和泛基因组学方法，筛选出Seppx05菌株缺失的和芝麻青枯菌群共有的Ⅲ型效应子基因等致病性相关基因；分别构建导入缺失基因或敲除共有基因的一系列Seppx05突变菌株，检测突变菌株对花生、辣椒、芝麻的致病力，以揭示致病基因对寄主的专化性及对寄主的选择性。以gfp为报告基因，跟踪野生菌株和致病基因突变菌株在花生、辣椒、芝麻根围的定殖及消长动态，阐明两类芝麻菌株与植物互作的生态适应性。上述研究结果，有望明确两类芝麻青枯菌株与寄主专化性及与寄主选择性有关的遗传学基础，为芝麻青枯病的有效治理提供理论依据。

芝麻是江西特色优势产业作物，青枯病发生严重。前期研究发现，大多数芝麻青枯菌都能侵染茄子、烟草、番茄、马铃薯、辣椒和花生，而来自江西鄱阳县的芝麻菌株Seppx05 能侵染茄子、烟草、番茄和马铃薯，却不能侵染花生和辣椒。为阐明其遗传学机理，本项研究测定了Seppx05 菌株的全基因组序列。采用比较基因组学方法分析，发现菌株Seppx05缺失了RipP1、RipS1、RipS3、RipU、RipAG、RipAH、RipAX2和RS_T3E_Hyp16Ⅲ 等8个Ⅲ型分泌系统效应子，特有RipAZ2和RipAL等2个Ⅲ型分泌系统效应子。根据这些效应子编码基因在芝麻青枯病菌内的分布频率，筛选出RipAZ2、RipAL、RipP1、RipU、RipAH和RipAX2等6个效应子编码基因构建突变体，并进行致病性及根围定殖能力测定，结果表明：（1）插入RipP1基因能使Seppx05菌株对花生和辣椒具有强致病力；插入RipU能使菌株Seppx05对花生具有弱致病力；且RipP1和RipU基因均具有促进菌株在花生和辣椒根围定殖的作用。说明RipP1和RipU基因与菌株Seppx05的寄主选择性相关。（2）敲除RipAL基因，虽然菌株在芝麻根围的定殖不受影响，但减弱了菌株对芝麻的致病力。证明RipAL基因对菌株Seppx05侵染芝麻起重要作用。综上分析发现，菌株Seppx05特有的RipAL基因是青枯菌侵染芝麻重要的Ⅲ型分泌系统效应子编码基因，而RipP1和RipU 2个Ⅲ型分泌系统效应子基因的缺失导致了青枯菌菌株Seppx05不能侵染花生和辣椒。本研究探明了青枯菌Seppx05 菌株能危害芝麻却不能侵染花生和辣椒的遗传学基础，不仅为芝麻、花生和辣椒抗病品种的选育奠定了理论基础，也为青枯病的综合治理提供了新思路。