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

The genus Savi (Leguminosae Juss.) comprises approximately 150 species, classified into five subgenera, most of which exhibit a diploid chromosome number of 2 = 22. However, the wild species (Benth) Verdc. (. subg. ) is notable for its dysploid chromosome number of 2 = 20. This study aimed to elucidate the chromosomal events involved in the karyotype evolution of (). We used oligopainting probes from chromosomes 1, 2, 3, and 5 of L. and two barcode probes from the genome of (L.) Walp. Additionally, bacterial artificial chromosomes (BACs) from and , along with a telomeric probe from (L.) Heynh., were hybridized to metaphase chromosomes to characterize 3, 7/5, and 9. Our findings revealed conserved oligo-FISH patterns on chromosomes 2, 6, 8, 10, and 11 between and Paracentric and pericentric inversions were identified for 3 and 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 , providing new insights into the evolutionary dynamics of the genus.