Ubc13 is required for Lys63-linked polyubiquitination and innate immune responses in mammals, but its functions in plant immunity still remain largely unknown. Here, we used molecular biological, pathological, biochemical, and genetic approaches to evaluate the roles of rice OsUbc13 in response to pathogens. The OsUbc13-RNA interference (RNAi) lines with lesion mimic phenotypes displayed a significant increase in the accumulation of flg22- and chitin-induced reactive oxygen species, and in defence-related genes expression or hormones as well as resistance to Magnaporthe oryzae and Xanthomonas oryzae pv oryzae. Strikingly, OsUbc13 directly interacts with OsSnRK1a, which is the α catalytic subunit of SnRK1 (sucrose non-fermenting-1-related protein kinase-1) and acts as a positive regulator of broad-spectrum disease resistance in rice. In the OsUbc13-RNAi plants, although the protein level of OsSnRK1a did not change, its activity and ABA sensitivity were obviously enhanced, and the K63-linked polyubiquitination was weaker than that of wild-type Dongjin (DJ). Overexpression of the deubiquitinase-encoding gene OsOTUB1.1 produced similar effects with inhibition of OsUbc13 in affecting immunity responses, M. oryzae resistance, OsSnRK1a ubiquitination, and OsSnRK1a activity. Furthermore, re-interfering with OsSnRK1a in one OsUbc13-RNAi line (Ri-3) partially restored its M. oryzae resistance to a level between those of Ri-3 and DJ. Our data demonstrate OsUbc13 negatively regulates immunity against pathogens by enhancing the activity of OsSnRK1a.

中文翻译：

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水稻泛素结合酶 OsUbc13 通过增强 OsSnRK1a 的活性负向调节针对病原体的免疫力

Ubc13 是哺乳动物中 Lys63 连接的多聚泛素化和先天免疫反应所必需的，但其在植物免疫中的功能仍然很大程度上未知。在这里，我们使用分子生物学、病理学、生化和遗传学方法来评估水稻 OsUbc13 在应对病原体中的作用。具有模拟病变表型的 OsUbc13 - RNA 干扰 (RNAi) 系显示出 flg22 和几丁质诱导的活性氧的积累、防御相关基因表达或激素以及对稻瘟病菌和米黄单胞菌的抗性显着增加。稻瘟病菌。引人注目的是，OsUbc13 直接与 OsSnRK1a 相互作用，OsSnRK1a 是 SnRK1（蔗糖非发酵 1 相关蛋白激酶 1）的 α 催化亚基，并作为水稻广谱抗病性的正调节因子。在OsUbc13 -RNAi植株中，虽然OsSnRK1a的蛋白水平没有变化，但其活性和ABA敏感性明显增强，且K63连接的多泛素化作用弱于野生型东金（DJ）。去泛素酶编码基因OsOTUB1.1的过度表达在影响免疫反应方面产生了与抑制OsUbc13类似的效果，M。米曲霉抗性、OsSnRK1a 泛素化和 OsSnRK1a 活性。此外，在一个OsUbc13 -RNAi 系 (Ri-3)中重新干扰OsSnRK1a部分恢复了其M。米曲霉的抗性水平介于 Ri-3 和 DJ 之间。我们的数据表明 OsUbc13 通过增强 OsSnRK1a 的活性来负向调节针对病原体的免疫力。