Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061-0329, USAChemistry Research Unit, Center of Medical, Agricultural, and Veterinary Entomology, US Department of Agriculture, Agricultural Research Service, Gainesville, FL 32608, USAVirginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061-0329, USA.
Plant J. 2012 Dec;72(6):882-93. doi: 10.1111/j.1365-313X.2012.05079.x. Epub 2012 Oct 26.
Diverse pathogens secrete effector proteins into plant cells to manipulate host cellular processes. Oomycete pathogens contain large complements of predicted effector genes defined by an RXLR host cell entry motif. The genome of Hyaloperonospora arabidopsidis (Hpa, downy mildew of Arabidopsis) contains at least 134 candidate RXLR effector genes. Only a small subset of these genes is conserved in related oomycetes from the Phytophthora genus. Here, we describe a comparative functional characterization of the Hpa RXLR effector gene HaRxL96 and a homologous gene, PsAvh163, from the Glycine max (soybean) pathogen Phytophthora sojae. HaRxL96 and PsAvh163 are induced during the early stages of infection and carry a functional RXLR motif that is sufficient for protein uptake into plant cells. Both effectors can suppress immune responses in soybean. HaRxL96 suppresses immunity in Nicotiana benthamiana, whereas PsAvh163 induces an HR-like cell death response in Nicotiana that is dependent on RAR1 and Hsp90.1. Transgenic Arabidopsis plants expressing HaRxL96 or PsAvh163 exhibit elevated susceptibility to virulent and avirulent Hpa, as well as decreased callose deposition in response to non-pathogenic Pseudomonas syringae. Both effectors interfere with defense marker gene induction, but do not affect salicylic acid biosynthesis. Together, these experiments demonstrate that evolutionarily conserved effectors from different oomycete species can suppress immunity in plant species that are divergent from the source pathogen's host.
不同的病原体将效应蛋白分泌到植物细胞中，以操纵宿主细胞过程。卵菌病原体包含大量预测的效应基因，这些基因由一个 RXLR 宿主细胞进入基序定义。 Hyaloperonospora arabidopsidis（Hpa，拟南芥霜霉病）的基因组至少包含 134 个候选 RXLR 效应基因。这些基因中只有一小部分在来自 Phytophthora 属的相关卵菌中保守。在这里，我们描述了 Hyaloperonospora arabidopsidis（Hpa，拟南芥霜霉病）的 RXLR 效应基因 HaRxL96 和同源基因 PsAvh163 的比较功能特征，该基因来自 Glycine max（大豆）病原体 Phytophthora sojae。HaRxL96 和 PsAvh163 在感染的早期阶段被诱导，并且携带一个功能齐全的 RXLR 基序，足以将蛋白质摄取到植物细胞中。这两个效应子都可以抑制大豆中的免疫反应。HaRxL96 抑制 Nicotiana benthamiana 中的免疫，而 PsAvh163 在 Nicotiana 中诱导类似于 HR 的细胞死亡反应，该反应依赖于 RAR1 和 Hsp90.1。表达 HaRxL96 或 PsAvh163 的转基因拟南芥植物对强毒和无毒 Hpa 的敏感性增加，并且对非致病性 Pseudomonas syringae 的几丁质沉积减少。这两个效应子都干扰防御标记基因的诱导，但不影响水杨酸的生物合成。总之，这些实验表明，来自不同卵菌物种的进化上保守的效应子可以抑制与来源病原体宿主不同的植物物种的免疫。
