Genomic approaches towardscharaterisationofsex linked genesin some imporantant genera ofcucurbita

Abstract

newline Sexual differentiation is a natural process for maintaining and sustaining genetic diversity in the eukaryotic system. In plants, multiple forms of sexual system are present to regulate and adopt ecological conditions. The presence of three major angiospermic sexual systems: bisexual, monoecy and dioecy and the existence of heteromorphic as well as homomorphic sex chromosomes makes the family Cucurbitaceae an ideal choice to study the mechanisms of sexual dimorphism. Momordica dioica is a perennial dioecious cucurbit with homomorphic sex chromosome and holds tactical advantage for early sex evolution. Although there are reports on the small genome size of this plant that has undergone seven transitions from dioecy to monoecy, the molecular mechanism governing its sexual development is still at its infancy. Likewise, Coccinia grandis is another important dioecious cucurbit with significant gender specific nutritional and medicinal properties besides having a small genome and heteromorphic sex chromosomes. However, studies on sexual evolution in this species is highly neglected with only little information available on its physical stage, genetic orientation and key sex determining factor. Therefore, the characterization of genetic elements responsible for sex expression and dimorphism in these dioecious cucurbits is the need of the hour. newlineIn our effort to early determination of sex in M. dioica because of its sex-specific medicinal and economic values, we used inter simple sequence repeat (ISSR) primers for developing a reliable molecular marker linked to sporophytic expression. Screening of bulked DNA pooled from male and female genotypes using 27 ISSR primers resulted in the detection of a male specific marker MdMSM. A sex-linked sequence tagged site (STS) marker MdY1 designed from MdMSM could efficiently differentiate the male and female M. dioica genotypes across different growth stages and geographical regions. Genome walking across the length of the sex-linked marker showed that MdY1 is highly homologous to the reverse transcriptase domain of a polyprotein and nested within a Copia-like retrotransposable element, MdRE1. Southern blot analysis revealed multiple copy locus and exclusive presence of MdY1 and MdRE1 only in the male genome