Genome-wide characterization and expression analysis of the gene family sheds light on powdery mildew resistance in .

MLO (mildew locus O) genes play a vital role in plant disease defense system, especially powdery mildew (PM). is a distinct Cucurbitaceae crop, and PM is one of the most serious diseases threatening crop production and quality. Although have been exploited in many Cucurbitaceae species, genome-wide mining of gene family in bottle gourd has not been surveyed yet. Here we identified 16 genes in our recently assembled genome. A total of 343 unique protein sequences from 20 species were characterized and compared to deduce a generally high level of purifying selection and the occurrence of regions related to candidate susceptibility factors in the evolutional divergence. were clustered in six clades containing seven conserved transmembrane domains and 10 clade-specific motifs along with deletion and variation. Three genes (, and ) in clade V showed high sequence identity with orthologues involved in PM susceptibility. The expression pattern of was tissue-specific but not cultivar-specific. Furthermore, it was indicated by qRT-PCR and RNA-seq that and were highly upregulated in response to PM stress. Subsequent sequence analysis revealed the structural deletion of and a single nonsynonymous substitution of in the PM-resistant genotype. Taken all together, it is speculated that is likely a major PM susceptibility factor. The results of this study provide new insights into family genes in bottle gourd and find a potential candidate S gene for PM tolerance breeding.