Ralstonia solanacearum Type III Effector RipAL Targets Chloroplasts and Induces Jasmonic Acid Production to Suppress Salicylic Acid-Mediated Defense Responses in Plants
Ralstonia solanacearum Type III Effector RipAL Targets Chloroplasts and Induces Jasmonic Acid Production to Suppress Salicylic Acid-Mediated Defense Responses in Plants
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DOI：
10.1093/pcp/pcy177
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发表时间：
2018-12-01
影响因子：
4.9
通讯作者：
Mukaihara, Takafumi
中科院分区：
文献类型：
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作者：
Nakano, Masahito;Mukaihara, Takafumi
青枯菌是引起植物青枯病的病原菌。这种病原体将70多种被称为RIPS(Ralstonia-Injected Proteins)的III型效应蛋白注入植物细胞，以成功感染。其中一个RIPP，RipAL，含有一个与拟南芥花药缺陷DHISCENCE1(DAD1)有同源性的脂肪酶结构域。RipAL显著抑制了烟草叶片的模式触发免疫。亚细胞定位分析表明，RipAL定位于叶绿体，并以植物细胞中的叶绿体脂为靶标。值得注意的是，RipAL的表达显著增加了植物叶片中茉莉酸(JA)和茉莉酸-异亮氨酸的水平，并诱导了茉莉酸信号标记基因的表达。同时，RipAL显著降低了水杨酸(SA)水平，降低了SA信号标记基因的表达水平。DAD1样脂酶结构域上两个假定的催化残基的突变取消了RipAL诱导JA产生和抑制SA信号转导的能力。青枯菌侵染还诱导了辣椒叶片中茉莉酸的产生，同时也降低了感病辣椒叶片中水杨酸的水平。沉默CaICS1基因可促进青枯病菌在植物中的生长，CaICS1编码SA合成酶1。这些结果表明SA信号参与了对青枯病菌的防御反应，青枯病菌利用RipAL诱导植物细胞产生JA并抑制SA信号。
Ralstonia solanacearum is the causal agent of bacterial wilt disease of plants. This pathogen injects more than 70 type III effector proteins called Rips (Ralstonia-injected proteins) into plant cells to succeed in infection. One of the Rips, RipAL, contains a putative lipase domain that shared homology with Arabidopsis DEFECTIVE IN ANTHER DEHISCENCE1 (DAD1). RipAL significantly suppressed pattern-triggered immunity in leaves of Nicotiana benthamiana. Subcellular localization analyses suggest that RipAL localizes to chloroplasts and targets chloroplast lipids in plant cells. Notably, the expression of RipAL markedly increased the jasmonic acid (JA) and JA-isoleucine levels, and induced the expressions of JA-signaling marker genes in plant leaves. Simultaneously, RipAL greatly reduced the salicylic acid (SA) level and decreased the expression levels of SA-signaling marker genes. Mutations in two putative catalytic residues in the DAD1-like lipase domain abolished the ability of RipAL to induce JA production and suppress SA signaling. Infection of R. solanacearum also induced JA production and simultaneously decreased the SA level in susceptible pepper leaves in a ripAL-dependent manner. The growth of R. solanacearum enhanced in plants with silenced CaICS1, which encodes the SA synthesis enzyme isochorismate synthase 1. These results indicate that SA signaling is involved in the defense response against R. solanacearum and that R. solanacearum uses RipAL to induce JA production and suppress SA signaling in plant cells.