Impact of polyploidization on genome evolution and phenotypic diversity in oil-tea Camellia

Oil-tea Camellia (OTC) is a valuable oil crop with diverse applications across the food, cosmetics, and medicine sectors. However, understanding the impact of chromosome polyploidization on genome evolution and phenotypic diversity in OTC remains challenging. This study addressed this knowledge gap by focusing on the origins and impacts of OTC polyploidization. The chromosomal karyotypes of 10 representative samples were examined, and their relationships were elucidated through hierarchical clustering analysis of karyotype parameters. Based on the phylogeny of the genus Camellia, the ancestral 1 C-value and 1 Cx-value were reconstructed, revealing an increase in the 1 C-value and a reduction in the 1 Cx-value associated with polyploidization. Notable positive correlations between ploidy level, genome size, and fruit size were highlighted by phylogenetic generalized least squares analysis. The phenotypic characteristics and chromosomal evolution of OTC were reconstructed. It was inferred that the genus Camellia, which was originally diploid, underwent 11 chromosomal duplication events. With the emergence of polyploidization, phenotypic traits transitioned from small fruits, autumn-winter flowering, and white flowers to larger fruits, spring flowering, and red flowers. Biogeographically, it is suggested that OTC first appeared in the Lingnan region, and subsequent species dispersion and hybridization significantly influenced the emergence of polyploid species. In conclusion, evidence has shown that OTC polyploidization increases genome size and enhances phenotypic diversity. This research enhances our understanding of the complex genetic mechanisms that drive species evolution, influence genome changes, and contribute to the domestication of Camellia plants. Furthermore, these findings offer insights that can inform future breeding and cultivation strategies for OTC.