Identification of novel sex determination loci in Japanese weedy melon

Abstract

AbstractSex expression contributes to fruit quality and yield in the Cucurbitaceae. In melon, orchestrated regulation by sex determination genes explains the mechanism of sex expression, resulting in a great variety of sexual morphologies. In this study, we examined the Japanese weedy melon UT1, which does not follow the reported model of sex expression. We conducted QTL analysis using F2plants for flower sex on the main stem and the lateral branch and mapped a “femaleness” locus on Chr. 3 (Fem3.1) and a “type of flower femaleness” (female or bisexual) locus on Chr. 8 (tff8.1).Fem3.1included the known sex determination geneCmACS11. Sequence comparison ofCmACS11between parental lines revealed three nonsynonymous SNPs. A CAPS marker developed from one of the SNPs was closely linked to femaleness in two F2populations with different genetic backgrounds. The femaleness allele was dominant in F1lines from crosses between UT1 and diverse cultivars and breeding lines. This study suggests that the identity oftff8.1isCmCPR5, a recently reported bisexual flower control gene. We found that the Japanese weedy melon UT1 does not follow the conventional sex expression model because of the interaction of the lociFem3.1andtff8.1with the previously reported sex determination genes. The results of this study provide new insights into the molecular mechanisms of sex determination in melons and considerations for the application of femaleness in melon breeding.Key messageJapanese weedy melon exhibits unique sex expression with interactions between previously reported sex determination genes and two novel loci.