Differential Expression under Podosphaera xanthii and Abiotic Stresses Reveals Candidate MLO Family Genes in Cucumis melo L

Abstract

Mildew Locus O (MLO) gene family members have significant functions in plant responses to biotic and abiotic stresses. Here, we retrieved 14 MLO sequences designated as Cucumis melo MLO (CmMLO) from the melon genome database ‘Melonomics’. Phylogenetic analysis distributed the 14 predicted CmMLO proteins into five of the six distinct MLO clades. Tissue-specific reverse-transcription quantitative PCR (RT-qPCR) analysis using the C. melo ‘SCNU1154’ line revealed that 14 CmMLO genes were differentially expressed, suggesting their probable roles in specific processes of growth and development. Analysis of stress-induced expression revealed that five of the CmMLO genes were upregulated at 6 h post inoculation (dpi) with Podosphaera xanthii Race 1 or DH487, indicating a possible role for MLO proteins in the host cell as an initial step of disease progress. Seven CmMLO genes were upregulated at 10 d post inoculation (dpi) with both races, timing that corresponds to disease appearance at the later stage of infection. RT-qPCR analysis also revealed that all 14 CmMLO genes were up-regulated under drought stress, 13 were upregulated under salt stress, 10 were upregulated under heat stress, 4 were upregulated under cold, and 12 were upregulated under abscisic acid (ABA) treatment. This information regarding the stress-responsive behavior of CmMLO genes creates a window for developing stress-resistant cultivars in the Cucurbitaceae.