Instituto de Hortofruticultura Subtropical y Mediterránea 'La Mayora', Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Depto. Biología Celular, Genética y Fisiología , Málaga, Spain.
Molecular Reprogramming and Evolution (MoRE) Lab, Centre for Research in Agricultural Genomics (CRAG), Carrer Vall Moronta Edifici CRAG, 08193, Barcelona, Spain.
J Exp Bot. 2021 Oct 26;72(20):7316-7334. doi: 10.1093/jxb/erab354.
Plants encode numerous intracellular receptors known as nucleotide-binding leucine-rich repeat receptors (NLRs) that recognize pathogen-derived effectors or their activity to activate defenses. miRNAs regulate NLR genes in many species, often triggering the production of phased siRNAs (phasiRNAs). Most such examples involve genes encoding NLRs carrying coiled-coil domains, although a few include genes encoding NLRs carrying a Toll/interleukin-1 domain (TNL). Here, we characterize the role of miR825-5p in Arabidopsis, using a combination of bioinformatics, transgenic plants with altered miRNA levels and/or reporters, small RNAs, and virulence assays. We demonstrate that miR825-5p down-regulates the TNL MIST1 by targeting for endonucleolytic cleavage the sequence coding for TIR2, a highly conserved amino acid motif, linked to a catalytic residue essential for immune function. miR825-5p acts as a negative regulator of basal resistance against Pseudomonas syringae. miR825-5p triggers the production from MIST1 of a large number of phasiRNAs that can mediate cleavage of both MIST1 and additional TNL gene transcripts, potentially acting as a regulatory hub. miR825-5p is expressed in unchallenged leaves and transcriptionally down-regulated in response to pathogen-associated molecular patterns (PAMPs). Our results show that miR825-5p, which is required for full expression of PAMP-triggered immunity, establishes a link between PAMP perception and expression of uncharacterized TNL genes.
植物编码了许多称为核苷酸结合亮氨酸重复受体（NLRs）的细胞内受体，这些受体可以识别病原体衍生的效应子或其活性，从而激活防御机制。miRNA 在许多物种中调节 NLR 基因，通常会触发相分离 siRNA（phasiRNA）的产生。大多数此类例子涉及编码带有卷曲螺旋结构域的 NLR 基因的例子，尽管有少数例子涉及编码带有 Toll/白细胞介素-1 结构域（TNL）的 NLR 基因的例子。在这里，我们使用生物信息学、改变 miRNA 水平和/或报告基因的转基因植物、小 RNA 和毒力测定的组合，来表征拟南芥中 miR825-5p 的作用。我们证明 miR825-5p 通过靶向编码 TIR2 的序列来下调 TNL MIST1，该序列编码高度保守的氨基酸基序，与免疫功能所必需的催化残基相连。miR825-5p 作为拟南芥对丁香假单胞菌基础抗性的负调节剂。miR825-5p 触发来自 MIST1 的大量 phasiRNA 的产生，这些 phasiRNA 可以介导 MIST1 和其他 TNL 基因转录本的切割，可能作为一个调节枢纽。miR825-5p 在未受挑战的叶片中表达，并在响应病原体相关分子模式（PAMP）时转录下调。我们的研究结果表明，miR825-5p 是 PAMP 触发免疫的完全表达所必需的，它在 PAMP 感知和未鉴定的 TNL 基因表达之间建立了联系。
