Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom.
Plant Cell. 2012 Mar;24(3):859-74. doi: 10.1105/tpc.111.095380. Epub 2012 Mar 9.
Analysis of tomato (Solanum lycopersicum) small RNA data sets revealed the presence of a regulatory cascade affecting disease resistance. The initiators of the cascade are microRNA members of an unusually diverse superfamily in which miR482 and miR2118 are prominent members. Members of this superfamily are variable in sequence and abundance in different species, but all variants target the coding sequence for the P-loop motif in the mRNA sequences for disease resistance proteins with nucleotide binding site (NBS) and leucine-rich repeat (LRR) motifs. We confirm, using transient expression in Nicotiana benthamiana, that miR482 targets mRNAs for NBS-LRR disease resistance proteins with coiled-coil domains at their N terminus. The targeting causes mRNA decay and production of secondary siRNAs in a manner that depends on RNA-dependent RNA polymerase 6. At least one of these secondary siRNAs targets other mRNAs of a defense-related protein. The miR482-mediated silencing cascade is suppressed in plants infected with viruses or bacteria so that expression of mRNAs with miR482 or secondary siRNA target sequences is increased. We propose that this process allows pathogen-inducible expression of NBS-LRR proteins and that it contributes to a novel layer of defense against pathogen attack.
对番茄（Solanum lycopersicum）小 RNA 数据集的分析揭示了一个影响抗病性的调控级联的存在。级联的启动子是 miRNA，它们属于一个异常多样化的超家族，其中 miR482 和 miR2118 是突出的成员。这个超家族的成员在不同物种中的序列和丰度是可变的，但所有变体都靶向具有核苷酸结合位点（NBS）和富含亮氨酸重复（LRR）基序的抗病蛋白 mRNA 序列中的 P 环基序编码序列。我们通过在 Nicotiana benthamiana 中的瞬时表达证实，miR482 靶向 N 端具有卷曲螺旋结构域的 NBS-LRR 抗病蛋白的 mRNA。这种靶向导致 mRNA 降解，并以依赖 RNA 依赖的 RNA 聚合酶 6 的方式产生次级 siRNA。这些次级 siRNA 中的至少一种靶向防御相关蛋白的其他 mRNA。在感染病毒或细菌的植物中，miR482 介导的沉默级联受到抑制，因此具有 miR482 或次级 siRNA 靶序列的 mRNA 的表达增加。我们提出，这个过程允许 NBS-LRR 蛋白的病原体诱导表达，并且它有助于对病原体攻击的防御的新层次。
