Genomic stability in Cenostigma Tul., (Caesalpinioideae, Fabaceae): causes and consequences

The Pantropical Caesalpinia group includes 225 species distributed in 27 monophyletic genera, among which Cenostigma stands out by taxonomic and phylogenetic complexity. The genus includes trees and shrubs with interspecific hybridization and high diversity in north-eastern Brazil (Caatinga domain). Detailed cytogenomic characterizations have been performed only in C. microphyllum revealing enrichment of long terminal repeats (LTR) Ty3/gypsy transposable elements (TEs) and satellite DNA (satDNA) in the heterochromatin. Here, we aimed to perform a comparative analysis of seven Northeast Brazilian species of Cenostigma using cytogenomic and genomic approaches. The comparative genomic analysis revealed repeats stability with similar TE abundance, composition, and chromosomal localization in all species. On the other hand, satDNA were highly variable in abundance, in some cases species-specific. Cytogenomic data confirmed the karyotype stability with the TE elements Athila and Tekay enriching the proximal heterochromatin. Moreover, the satDNA CemiSat163 appeared to be exclusively located on acrocentric chromosomes of the analysed species. The genomic stability in Cenostigma may be related to their relatively recent age (13.59 Mya), long-life cycle, and/ or similarity in ecological niche among this species. We propose that the genomic stability found in Cenostigma may facilitate the natural interspecific gene flow reported in sympatric species, complicating the interpretation of its systematics and evolution.