Plant mildew-resistance locus O (MLO) proteins influence susceptibility to powdery mildew. However, their roles in plant responses to other pathogens and heat stress remain unclear. Here, we showed that CaMLO6, a pepper (Capsicum annuum) member of MLO clade V, is a protein targeted to plasma membrane and probably endoplasmic reticulum. The transcript expression level of CaMLO6 was upregulated in the roots and leaves of pepper plants challenged with high-temperature-high-humidity (HTHH), and was upregulated in leaves but downregulated in roots of plants infected with the bacterial pathogen Ralstonia solanacearum. CaMLO6 was also directly upregulated by CaWRKY40 upon HTHH but downregulated by CaWRKY40 upon R. solanacearum infection. Virus-induced gene silencing of CaMLO6 significantly decreased pepper HTHH tolerance and R. solanacearum susceptibility. Moreover, CaMLO6 overexpression enhanced the susceptibility of Nicotiana benthamiana and pepper plants to R. solanacearum and their tolerance to HTHH, effects that were associated with the expression of immunity- and thermotolerance-associated marker genes, respectively. These results suggest that CaMLO6 acts as a positive regulator in response to HTHH but a negative regulator in response to R. solanacearum. Moreover, CaMLO6 is transcriptionally affected by R. solanacearum and HTHH; these transcriptional responses are at least partially regulated by CaWRKY40.

中文翻译：

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胡椒 CaMLO6 负向调节青枯菌抗性，正向调节高温和高湿反应。


植物抗霉基因座 O (MLO) 蛋白影响白粉病的易感性。然而，它们在植物对其他病原体和热应激反应中的作用仍不清楚。在这里，我们证明 CaMLO6 是 MLO 进化枝 V 的辣椒 (Capsicum annuum) 成员，是一种靶向质膜并可能靶向内质网的蛋白质。在受到高温高湿（HTHH）攻击的辣椒植物的根和叶中，CaMLO6的转录物表达水平上调；而在感染细菌病原体青枯菌的植物中，叶子中的CaMLO6转录物表达水平上调，但在根部中下调。 HTHH 后 CaWRKY40 直接上调 CaMLO6，但青枯菌感染后 CaWRKY40 下调 CaMLO6。病毒诱导的 CaMLO6 基因沉默显着降低了辣椒 HTHH 耐受性和青枯菌敏感性。此外，CaMLO6 过表达增强了本塞姆氏烟草和辣椒植物对青枯菌的敏感性及其对 HTHH 的耐受性，这些效应分别与免疫相关标记基因和耐热相关标记基因的表达相关。这些结果表明，CaMLO6 作为响应 HTHH 的正调节因子，但作为响应青枯菌的负调节因子。此外，CaMLO6 的转录受到青枯菌和 HTHH 的影响。这些转录反应至少部分受到 CaWRKY40 的调节。