School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv, 69978, Israel.
Plant J. 2020 Dec;104(5):1369-1381. doi: 10.1111/tpj.15006. Epub 2020 Oct 23.
The first line of plant defense occurs when a plant pattern recognition receptor (PRR) recognizes microbe-associated molecular patterns. Plant PRRs are either receptor-like kinases (RLKs), which have an extracellular domain for ligand binding, a single-pass transmembrane domain, and an intracellular kinase domain for activating downstream signaling, or receptor-like proteins (RLPs), which share the same overall structure but lack an intracellular kinase domain. The tomato (Solanum lycopersicum) LeEIX2 is an RLP that binds ethylene-inducing xylanase (EIX), a fungal elicitor. To identify LeEIX2 receptor interactors, we conducted a yeast two-hybrid screen and found a tomato protein that we termed SlRLK-like. The interaction of LeEIX2 with SlRLK-like was verified using co-immunoprecipitation and bimolecular fluorescence complementation assays. The defense responses induced by EIX were markedly reduced when SlRLK-like was overexpressed in Nicotiana benthamiana or Nicotiana tabacum, and knockout of SlRLK-like using the CRISPR/Cas9 system increased EIX-induced ethylene production and 1-aminocyclopropane-1-carboxylate synthase (SlACS2) gene expression in tomato. Co-expression of SlRLK-like with LeEIX2 led to a reduction in its abundance, apparently through an endoplasmic reticulum-associated degradation process. Notably, truncation of SlRLK-like protein revealed that the malectin-like domain is sufficient and essential for its function. Moreover, SlRLK-like associated with the RLK FLS2, resulting in its degradation and concomitantly a reduction of the flagellin 22 (flg22)-induced burst of reactive oxygen species. In addition, SlRLK-like co-expression with other RLPs, Ve1 and AtRLP23, also led to a reduction in their abundance. Our findings suggest that SlRLK-like leads to a decreased stability of various PRRs, leading to a reduction in their abundance and resulting in attenuation of defense responses.
植物防御的第一道防线是当植物模式识别受体 (PRR) 识别微生物相关分子模式时发生的。植物 PRR 要么是受体样激酶 (RLK)，其具有用于配体结合的细胞外结构域、单次跨膜结构域和用于激活下游信号转导的细胞内激酶结构域，要么是受体样蛋白 (RLP)，其具有相同的整体结构，但缺乏细胞内激酶结构域。番茄 (Solanum lycopersicum) LeEIX2 是一种结合乙烯诱导木聚糖酶 (EIX) 的 RLP，EIX 是一种真菌激发子。为了鉴定 LeEIX2 受体相互作用蛋白，我们进行了酵母双杂交筛选，发现了一种我们称之为 SlRLK-like 的番茄蛋白。使用共免疫沉淀和双分子荧光互补测定验证了 LeEIX2 与 SlRLK-like 的相互作用。当 SlRLK-like 在烟草原生质体或烟草中过表达时，EIX 诱导的防御反应明显降低，并且使用 CRISPR/Cas9 系统敲除 SlRLK-like 会增加番茄中 EIX 诱导的乙烯产生和 1-氨基环丙烷-1-羧酸合酶 (SlACS2) 基因表达。SlRLK-like 与 LeEIX2 的共表达导致其丰度降低，显然是通过内质网相关降解过程。值得注意的是，SlRLK-like 蛋白的截断表明其甘露糖结合样结构域是其功能所必需的。此外，SlRLK-like 与 RLK FLS2 相关联，导致其降解，并随之减少 flagellin 22 (flg22) 诱导的活性氧爆发。此外，SlRLK-like 与其他 RLPs，Ve1 和 AtRLP23 的共表达也导致其丰度降低。我们的研究结果表明，SlRLK-like 导致各种 PRR 的稳定性降低，导致其丰度降低，并导致防御反应减弱。
