Dynamics of sex expression and chromosome diversity in Cucurbitaceae: a story in the making

Abstract

The family Cucurbitaceae showcases a wide range of sexual phenotypes being variedly regulated by biological and environmental factors. In the present context, we have tried to assemble reports of cytogenetic investigations carried out in cucurbits accompanied by information on sex expression diversities and chromosomal or molecular basis of sex determination in dioecious (or other sexual types, if reported) taxa known so far. Most of the Cucurbitaceae tribes have mixed sexual phenotypes with varying range of chromosome numbers and hence, ancestral conditions become difficult to probe. Occurrence of polyploidy is rare in the family and has no influence on sexual traits. The sex determination mechanisms have been elucidated in some well-studied taxa like Bryonia,Coccinia and Cucumis showing interplay of genic, biochemical, developmental and sometimes chromosomal determinants. Substantial knowledge about genic and molecular sex differentiation has been obtained for genera like Momordica, Cucurbita and Trichosanthes. The detailed information on sex determination schemes, genomic sequences and molecular phylogenetic relationships facilitate further comprehensive investigations in the tribe Bryonieae. The discovery of organ identity genes and sex-specific sequences regulating sexual behaviour in Coccinia,Cucumis and Cucurbita opens up opportunities of relevant investigations to answer yet unaddressed questions pertaining to floral unisexuality, dioecy and chromosome evolution in the family. The present discussion brings the genera in light, previously recognized under subfamily Nhandiroboideae, where the study of chromosome cytology and sex determination mechanisms can simplify our understanding of sex expression pathways and its phylogenetic impacts.

Draft genome sequence of bitter gourd (Momordica charantia), a vegetable and medicinal plant in tropical and subtropical regions

“…Cucurbit crops are suitable models for elucidating sex determination in monoecious plant species 42 . Since genes for sex determination have been identified in melon and cucumber, their orthologous genes were further explored in other Cucurbitaceae crops by BLAST searching, including bitter gourd.…”

Molecular cloning, characterization and expression analysis of MADS-box genes associated with reproductive development in Momordica dioica Roxb.

“…This suggest that the M. dioica MADS-box genes do not have duplicated loci as evident in other members of the Cucurbitaceae family (Hu and Liu 2012;Hao et al 2016). A possible reason for this could be the presence of a diploid genome (2n = 28), asymmetric karyotypes and autopolyploid origin of the cultivated populations in M. dioica (Bhowmick and Jha 2015). Besides, a previously reported tetraploid nature of M. dioica genome has been recently negated due to misrepresentation of a related species (Bharathi et al 2011).…”

Cucurbit Genomics Database (CuGenDB): a central portal for comparative and functional genomics of cucurbit crops

“…Moreover, several species such as pumpkin and bottle gourd have been used as rootstocks for other cucurbit crops in order to enhance tolerance to soil-borne diseases and abiotic stresses and to improve fruit yield and quality (2). Furthermore, the cucurbit species have long served as model systems for studies of fundamental biological processes such as fruit ripening (3), sex determination (4), and vascular development (5). In addition, both xylem and phloem sap of cucurbits can be readily collected for studies on long-distance signaling events (6).…”