In plants, high disease resistance often results in a reduction of yield. Therefore, breeding crops with balanced yield and disease resistance has become a major challenge. Recently, microRNA (miRNA)-mediated R gene turnover has been shown to be a protective mechanism used by plants to prevent autoimmunity in the absence of pathogens. However, whether these miRNAs play a role in plant growth and how miRNA-mediated R gene turnover responds to pathogen infection have rarely been explored. Here, we found that a Brassica miRNA, miR1885, targets both an immune receptor gene and a development-related gene for negative regulation through distinct modes of action. MiR1885 directly silences the TIR-NBS-LRR class of R gene BraTNL1 but represses the expression of the photosynthesis-related gene BraCP24 by targeting the Trans-Acting Silencing (TAS) gene BraTIR1 for trans-acting small interfering RNAs (tasiRNAs)-mediated silencing. We found that, under natural conditions, miR1885 was kept at low levels to maintain normal development and basal immunity but peaked during the floral transition to promote flowering. Interestingly, upon Turnip mosaic virus (TuMV) infection, miR1885-dependent trans-acting silencing of BraCP24 was enhanced to speed up the floral transition, whereas miR1885-mediated R gene turnover was overcome by TuMV-induced BraTNL1 expression, reflecting precise regulation of the arms race between plants and pathogens. Collectively, our results demonstrate that a single Brassica miRNA dynamically regulates both innate immunity and plant growth and responds to viral infection, revealing that Brassica plants have developed a sophisticated mechanism in modulating the interplay between growth, immunity, and pathogen infection.

在植物中，高抗病性通常导致产量降低。因此，育种具有平衡产量和抗病性的农作物已经成为主要挑战。最近，微小RNA（miRNA）介导的R基因更新已被证明是植物用于在没有病原体的情况下防止自身免疫的保护机制。然而，很少探讨这些miRNA是否在植物生长中起作用以及miRNA介导的R基因更新如何响应病原体感染。在这里，我们发现芸苔属miRNA miR1885既针对免疫受体基因，又针对与发育相关的基因，通过不同的作用方式进行负调控。MiR1885直接沉默R基因BraTNL1的TIR-NBS-LRR类但压制光合作用相关的基因的表达BraCP24通过靶向反式作用沉默（TAS）基因BraTIR1为反式作用小干扰RNA（tasiRNAs）介导的沉默。我们发现，在自然条件下，miR1885保持在较低水平以维持正常发育和基础免疫，但在花期过渡期间达到高峰以促进开花。有趣的是，在芜菁花叶病毒（芜菁花叶病毒）感染，miR1885依赖性反式的式作用沉默BraCP24得到增强，加速花转变，而miR1885介导řTuMV诱导的BraTNL1表达克服了基因更新，这反映了植物与病原体之间军备竞赛的精确调节。总体而言，我们的结果表明，单个芸苔属miRNA可动态调节先天免疫力和植物生长并响应病毒感染，这表明芸苔属植物已开发出一种复杂的机制来调节生长，免疫力和病原体感染之间的相互作用。