Chromosome number evolution in dalbergioid legumes (Papilionoideae, Leguminosae)

Abstract

The dalbergioids, one of the largest clades among legumes, present significant karyotype diversity. Previous studies suggested different base chromosome numbers, hampering the understanding of karyotype evolution in dalbergioid legumes. In this study, we integrated chromosome numbers from the literature with phylogenetic data and new cytogenetic data for six species aiming to clarify the paths of karyotype evolution. We could confirm the base chromosome number of dalbergioid legumes asx = 10, which was constant for the three dalbergioid clades, namely Adesmia, Dalbergia, and Pterocarpus. However, we found alternative base chromosome numbers for some genera, which illustrate the two main mechanisms of chromosome changes found in dalbergioids: polyploidy and dysploidy. Considering the first diverging lineages in the phylogeny, polyploidy and dysploidy could be detected in seven and three nodes, respectively, with two out of the three dysploidy events associated with polyploidy. Nevertheless, considering the chromosome changes within species, the descendent dysploidy was the most common event in dalbergioid legumes. Such a high frequency of dysploidy highlights the importance of studying multiple populations from each species. In addition, the chromosome banding revealed DAPI(+)bands, which is not commonly found in plants, as a possible chromosome marker forStylosanthes. The chromosome banding analysis has taxonomic potential and could be explored in future studies to better understand the complex taxonomic groups inside dalbergioid legumes.