Chromosomal localization of 45S rDNA, sex-specific C values, and heterochromatin distribution in Coccinia grandis (L.) Voigt

Abstract

Coccinia grandis is a widely distributed dioecious cucurbit in India, with heteromorphic sex chromosomes and X-Y sex determination mode. The present study aids in the cytogenetic characterization of four native populations of this plant employing distribution patterns of 45S rDNA on chromosomes and guanine-cytosine (GC)-rich heterochromatin in the genome coupled with flow cytometric determination of genome sizes. Existence of four nucleolar chromosomes could be confirmed by the presence of four telomeric 45S rDNA signals in both male and female plants. All four 45S rDNA sites are rich in heterochromatin evident from the co-localization of telomeric chromomycin A (CMA)(+ve) signals. The size of 45S rDNA signal was found to differ between the homologues of one nucleolar chromosome pair. The distribution of heterochromatin is found to differ among the male and female populations. The average GC-rich heterochromatin content of male and female populations is 23.27 and 29.86 %, respectively. Moreover, the male plants have a genome size of 0.92 pg/2C while the female plants have a size of 0.73 pg/2C, reflecting a huge genomic divergence between the genders. The great variation in genome size is owing to the presence of Y chromosome in the male populations, playing a multifaceted role in sexual divergence in C. grandis.

The Sister Chromatid Division of the Heteromorphic Sex Chromosomes in Silene Species and Their Transmissibility towards the Mitosis

“…Although, large heteromorphic sex chromosomes have been described in only 18 plant species to date, similarly as in S. latifolia and S. dioica , there are several other species that possess large and heteromorphic sex chromosomes, as described in Coccinia grandis (the Y is 2.2× larger than the X [ 14 ]) or Rumex acetosa (the X chromosome is the largest in the genome [ 12 ]). The overall Y chromosome size variation between populations of C. grandis [ 42 ] further shows the ongoing process of non-recombining region expansion which might be limited by its spindle axis length similarly to Silene .…”

A critical review on cytogenetics of Cucurbitaceae with updates on Indian taxa

“…Presently an enzymatic maceration and air drying ( EMA ) method followed by flurochrome banding has been employed as per our previous protocols ( Bhowmick et al 2012 , 2016 ; Bhowmick and Jha 2015a , 2019 , 2021 ) to represent fresh karyotypes of seven agriculturally important cucurbit species (Table 1 ) belonging to Benincaseae and Sicyoeae . Fresh and healthy roots were used from different sources (like germinating seeds, seedlings and underground root stocks).…”

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

“…In the gourd family (Cucurbitaceae), flowers are represented by all the three major sexual patternsmonoecy, dioecy and hermaphrodite representing a distinct sexual dimorphism and evolution among the angiosperms. Although, major Cucurbitaceous genus such as Bryonia, Coccinia and Trichoxanthes have been well-documented to understand the genetics of sex determination (Volz and Renner 2008;Ming et al 2011;Bhowmick et al 2016;Mohanty et al 2017), comparatively little or no interest has been attributed to the sexual development in Momordica, a genus with multiple perennial species that has undergone seven transitions from dioecy to monoecy (Schaefer and Renner 2010). Momordica dioica (spiny gourd) is a prominent dioecious member of this genus with a small genome size and an incipient set of homomorphic sex chromosomes that could be used as a sculpt for studying sexual phenotypes.…”