Chromosomal localization of 45S rDNA, sex-specific C values, and heterochromatin distribution in Coccinia grandis (L.) Voigt
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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.
KeywordsCoccinia grandis 45S rDNA FISH CMA Flow cytometry Genome size
BKB is thankful to Department of Science and Technology, Govt. of India, for the award of INSPIRE Fellowship. We are grateful to Drs. T. Yamamoto and S. Terakami of the National Institute of Fruit Tree Science, Japan for providing rDNA fragment for FISH. We thank Prof. Jaroslav Doležel, Institute of Experimental Botany, Olomouc, Czech Republic for the provision of seeds for reference standard. BKB expresses sincere gratitude to Prof. Timir Baran Jha for his help and guidance in fluorescence banding technique. We also thank CU- BD CoE for Nanobiotechnology, CRNN, University of Calcutta for instrument facilities. Financial assistance from Department of Biotechnology (GOI, Sanction No BT/ PR3919/PBD/16/959/2011) is gratefully acknowledged.
Conflict of interest
The authors declare that they have no conflict of interest.
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