Analysis of Expression, Mutation, and Alternative Splice Variants of Candidate Genes, MLO2 and MLO6A, Involved in Powdery Mildew Susceptibility in Mulberry (Morus spp.)

Mulberry is a fast-growing perennial crop commercially exploited as the sole source of food for the mulberry silkworm, Bombyx mori, for the production of silk. Powdery mildew disease is a major foliar disease that greatly affects the sericulture industry. Understanding the genetic basis of powdery mildew disease resistance and its utilization for developing resistant varieties is the primary approach to mulberry crop improvement. Both natural and induced mutations impairing the function of the Mildew resistance Locus O (MLO) gene leading to powdery mildew resistance have been identified in different crop plants. However, more studies are required focusing on MLO gene-based resistance in natural germplasm. In this study, previously identified candidate genes, MLO2 and MLO6A, involved in powdery mildew susceptibility in mulberry were analyzed for gene expression, mutation, and alternative splice variants. In some tolerant accessions, MLO2 and MLO6A show either reduced or no elevated expression under infected conditions. Publicly available whole genome re-sequenced data analysis from mulberry accessions identified single amino acid substitutions in the MLO2 and MLO6A genes. Further, alternative splice variants of intron retention and exon skipping resulted in premature stop codon leading to the production of truncated MLO2 protein which were detected in tolerant mulberry accessions. This study will pave for better understanding of powdery mildew disease resistance and for breeding program.