MicroRNA (miRNA)-mediated post-transcriptional regulation plays a vital role in the response of plants to pathogens. Although the microRNA397 family has been implicated in physiological processes as an important regulator, little is known about its function in the resistance of plants to pathogens. Here, Malus hupehensis miR397, which was induced by Botryosphaeria dothidea infection, was identified to directly target M. hupehensis Laccase7 (MhLAC7). The expression analysis of mature Mh-miR397 and MhLAC7 revealed their partly opposite expression patterns. The coexpression of Mh-miR397b in MhLAC7 overexpressing Nicotiana benthamiana suppressed the accumulation of exogenous MhLAC7 and endogenous NbLAC7, which led to decreased lignin content and reduced plant resistance to Botrytis cinerea. As reflected by increasing disease severity and pathogen growth, overexpression of miR397b in both the resistant M. hupehensis and susceptible M. domestica 'Gala' resulted in an increased sensitivity to B. dothidea infection, owing to reduced LAC7 expression and lignin content; however, the inhibition of miR397 had opposite effects. MicroRNA397 functions as a negative regulator in the resistance of Malus to B. dothidea by modulating the LAC7 expression and lignin biosynthesis.

中文翻译：

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MicroRNA397b 通过调节参与木质素生物合成的 MhLAC7 负调控湖北苹果对 Botryosphaeria dothidea 的抗性

MicroRNA (miRNA) 介导的转录后调控在植物对病原体的反应中起着至关重要的作用。尽管 microRNA397 家族作为一个重要的调节因子参与了生理过程，但对其在植物抵抗病原体方面的功能知之甚少。在这里，由 Botryosphaeria dothidea 感染诱导的 Malus hupehensis miR397 被鉴定为直接靶向 M. hupehensis Laccase7 (MhLAC7)。成熟 Mh-miR397 和 MhLAC7 的表达分析揭示了它们部分相反的表达模式。Mh-miR397b 在过表达本氏烟草的 MhLAC7 中的共表达抑制了外源 MhLAC7 和内源 NbLAC7 的积累，从而导致木质素含量降低和植物对灰葡萄孢的抗性降低。正如疾病严重程度和病原体生长的增加所反映的那样，由于 LAC7 表达和木质素含量降低，miR397b 在抗性湖北 M. hupehensis 和易感 M.domestica 'Gala' 中的过表达导致对 B. dothidea 感染的敏感性增加；然而，抑制 miR397 具有相反的效果。MicroRNA397 通过调节 LAC7 表达和木质素生物合成，在 Malus 对 B. dothidea 的抗性中起负调节作用。