1 Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, U.S.A.
2 Department of Biology, Indiana University, Bloomington, IN, U.S.A.
Mol Plant Microbe Interact. 2019 May;32(5):550-565. doi: 10.1094/MPMI-07-18-0202-FI. Epub 2019 Apr 1.
The cysteine protease AvrPphB activates the resistance protein RPS5 by cleaving a second host protein, PBS1. AvrPphB induces defense responses in other plant species, but the genes and mechanisms mediating AvrPphB recognition in those species have not been defined. Here, we show that AvrPphB induces defense responses in diverse barley cultivars. We also show that barley contains two orthologs, that their products are cleaved by AvrPphB, and that the barley AvrPphB response maps to a single locus containing a nucleotide-binding leucine-rich repeat (NLR) gene, which we termed (). Transient coexpression of PBR1 with wild-type AvrPphB but not with a protease inactive mutant triggered defense responses, indicating that PBR1 detects AvrPphB protease activity. Additionally, PBR1 coimmunoprecipitated with barley and PBS1 proteins, suggesting mechanistic similarity to detection by RPS5. Lastly, we determined that wheat cultivars also recognize AvrPphB protease activity and contain two putative orthologs. Phylogenetic analyses showed, however, that is not orthologous to . Our results indicate that the ability to recognize AvrPphB evolved convergently and imply that selection to guard PBS1-like proteins occurs across species. Also, these results suggest that PBS1-based decoys may be used to engineer protease effector recognition-based resistance in barley and wheat.
半胱氨酸蛋白酶 AvrPphB 通过切割第二个宿主蛋白 PBS1 来激活抗性蛋白 RPS5。AvrPphB 在其他植物物种中诱导防御反应，但介导这些物种中 AvrPphB 识别的基因和机制尚未确定。在这里，我们表明 AvrPphB 在不同的大麦品种中诱导防御反应。我们还表明，大麦含有两个同源物，它们的产物被 AvrPphB 切割，并且大麦 AvrPphB 反应映射到一个包含核苷酸结合富含亮氨酸重复 (NLR) 基因的单一基因座，我们将其命名为 (). 野生型 AvrPphB 与瞬时共表达的 PBR1 而不是与蛋白酶失活突变体共表达会触发防御反应，表明 PBR1 检测到 AvrPphB 蛋白酶活性。此外，PBR1 与大麦和 PBS1 蛋白共免疫沉淀，表明与 RPS5 的检测具有机制相似性。最后，我们确定小麦品种也能识别 AvrPphB 蛋白酶活性，并含有两个推定的 同源物。然而，系统发育分析表明， 与 不是同源的。我们的结果表明，识别 AvrPphB 的能力是趋同进化的，并暗示针对 PBS1 样蛋白的选择发生在不同物种之间。此外，这些结果表明，基于 PBS1 的诱饵可能用于在大麦和小麦中工程化基于蛋白酶效应子识别的抗性。
