Powdery mildew (PM) disease is one of the most serious threats to Momordica charantia. Specific mildew resistance locus O (MLO) genes associated with PM susceptibility have been explored in some plant species for mlo-based PM resistance. However, MLO has not been surveyed globally for candidate susceptibility factors in M. charantia. In this study, 15 MLO genes, designated McMLO1∼15, were identified in the recently reported M. charantia genome. Phylogenetic analysis clustered McMLOs into five clades. In clade V, McMLO3, McMLO4, McMLO6, and McMLO11 co-clustered with the known PM susceptibility (PMS) factors of dicotyledonous plants, making them putative PMS factors in M. charantia (McPMS). Three of the four McPMS candidates, McMLO4, McMLO6, and McMLO11, showed much higher sequence identity with PMS-related orthologues than with paralogues. Structure modelling and alignment revealed significant structural similarity between McMLO11 and McMLO4 and the functionally characterized PMS CsMLO8, CmMLO2, and CsMLO11. High structural similarity was also found between McMLO11 and McMLO6 but not between McMLO3 and any other MLO homologs. RNA-seq indicated that the four McPMS candidates were all specifically expressed at the highest level in leaves compared with other tissues. Furthermore, among the expressed McMLOs in leaves, McMLO6 was expressed at the lowest level, McMLO11, McMLO3 and McMLO4 were expressed at the first, second and fourth highest levels, respectively. During PM infection, McMLO11 was moderately induced but highly expressed at the highest level. McMLO4 and McMLO6 were significantly upregulated, but there was no significant differential expression of McMLO3. Consistent with the different expression profiles of the four McPMSs, different types and amounts of cis-acting regulatory elements were found in their promoters. Taken together, we speculate that in M. charantia McMLO4 is a minor PMS factor, and that McMLO11 is the major PMS factor and is functionally redundant with McMLO6. McMLO3 seems to be a unique PMS factor with a different functional mechanism. The results of the study provide valuable information for further study of mlo-based PM resistance improvement in M. charantia.

白粉病是对苦瓜的最严重威胁之一。在某些植物物种中，已经发现了与PM易感性相关的特定霉菌抗性基因座O（MLO）基因对基于mlo的PM抗性。但是，尚未在全球范围内针对M. charantia中的候选易感因素对MLO进行过调查。在这项研究中，在最近报道的M. charantia基因组中鉴定出15个MLO基因，命名为McMLO1-15。系统发育分析将McMLOs分为五个进化枝。在进化枝V，McMLO3，McMLO4，McMLO6和McMLO11与已知的双子叶植物的PM易感性（PMS）因子共同聚类，使它们在M. charantia（McPMS）中被推定为PMS因子。四三名McPMS候选人，McMLO4，McMLO6和McMLO11，显示出高得多的序列相同PMS-相关直向比旁系同源物。结构建模和比对揭示了McMLO11和McMLO4与功能上已表征的PMS CsMLO8，CmMLO2和CsMLO11之间的显着结构相似性。在McMLO11和McMLO6之间也发现了高度的结构相似性，但在McMLO3和任何其他MLO同源物之间没有发现。RNA-seq表示四个McPMS与其他组织相比，所有候选植物均在叶片中最高表达。此外，在叶片中表达的McMLO中，McMLO6以最低水平表达，McMLO11，McMLO 3和McMLO4分别以第一，第二和第四高水平表达。在PM感染期间，McMLO11被中等程度诱导，但在最高水平上高表达。McMLO 4和McMLO6被显着上调，但是McMLO3没有明显的差异表达。与四个McPMS的不同表达谱一致，在其启动子中发现了不同类型和数量的顺式作用调节元件。两者合计，我们推测在M. charantia中， McMLO4是次要的PMS因子，而McMLO11是主要的PMS因子，并且在功能上与McMLO6无关。McMLO3似乎是具有不同功能机制的独特PMS因子。该研究结果为进一步研究的有价值的信息MLO在下午基于性的提高苦瓜。