“End-to-End Chromosome Fusion” as the Main Driver of Descending Dysploidy in Vigna lasiocarpa (Mart. ex Benth.) Verdc. (Leguminosae Juss.)

The genus <i>Vigna</i> Savi (Leguminosae Juss.) comprises approximately 150 species, classified into five subgenera, most of which exhibit a diploid chromosome number of 2<i>n</i> = 22. However, the wild species <i>Vigna lasiocarpa</i> (Benth) Verdc. (<i>V</i>. subg. <i>Lasiospron</i>) is notable for its dysploid chromosome number of 2<i>n</i> = 20. This study aimed to elucidate the chromosomal events involved in the karyotype evolution of <i>V. lasiocarpa</i> (<i>Vla</i>). We used oligopainting probes from chromosomes 1, 2, 3, and 5 of <i>Phaseolus vulgaris</i> L. and two barcode probes from the genome of <i>V. unguiculata</i> (L.) Walp. Additionally, bacterial artificial chromosomes (BACs) from <i>V. unguiculata</i> and <i>P. vulgaris</i>, along with a telomeric probe from <i>Arabidopsis thaliana</i> (L.) Heynh., were hybridized to <i>V. lasiocarpa</i> metaphase chromosomes to characterize <i>Vla</i>3, <i>Vla</i>7/5, and <i>Vla</i>9. Our findings revealed conserved oligo-FISH patterns on chromosomes 2, 6, 8, 10, and 11 between <i>V. unguiculata</i> and <i>V. lasiocarpa.</i> Paracentric and pericentric inversions were identified for <i>Vla</i>3 and <i>Vla</i>9, respectively. Our integrative approach revealed that the dysploid chromosome originated from an "end-to-end fusion" of homoeologous chromosomes 5 and 7. This is the first report on the chromosomal mechanisms underlying descending dysploidy in <i>Vigna</i>, providing new insights into the evolutionary dynamics of the genus.