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.

中文翻译：

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SlRLK-like 是一种类似 malectin 的结构域蛋白，影响 LeEIX2 受体的定位和丰度，从而抑制 EIX 诱导的免疫反应


当植物模式识别受体（PRR）识别微生物相关分子模式时，植物防御的第一道防线就会出现。植物 PRR 要么是受体样激酶 (RLK)，其具有用于配体结合的胞外结构域、单次跨膜结构域和用于激活下游信号传导的胞内激酶结构域，要么是受体样蛋白 (RLP)，其共享整体结构相同，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)（一种真菌激发子）的 RLP。为了识别 LeEIX2 受体相互作用蛋白，我们进行了酵母双杂交筛选，发现了一种我们称为 SlRLK 样的番茄蛋白。使用免疫共沉淀和双分子荧光互补测定验证了 LeEIX2 与 SlRLK 样的相互作用。当 SlRLK-like 在本塞姆氏烟草或烟草中过表达时，EIX 诱导的防御反应显着降低，并且使用 CRISPR/Cas9 系统敲除SlRLK-like增加了 EIX 诱导的乙烯产生和 1-氨基环丙烷-1-羧酸合酶（ SlACS2 ) 番茄中的基因表达。 SlRLK 样与 LeEIX2 的共表达导致其丰度减少，显然是通过内质网相关的降解过程。值得注意的是，SlRLK 样蛋白的截短表明，malectin 样结构域对其功能来说是足够且必需的。此外，SlRLK 样与 RLK FLS2 相关，导致其降解，并同时减少鞭毛蛋白 22 (flg22) 诱导的活性氧爆发。 此外，SlRLK 与其他 RLP、Ve1 和 AtRLP23 的共表达也导致其丰度减少。我们的研究结果表明，SlRLK 样会导致各种 PRR 的稳定性降低，从而导致其丰度减少并导致防御反应减弱。