Evolution of chloroplast genomes promoted adaptation to diverse ecological habitats.

The course, tempo and mode of chloroplast genome evolution remain largely unknown, resulting in limited knowledge about how plant plastome gene and genome evolve during the process of recent plant speciation. Here, we report the complete plastomes of 22 closely related species in chronologically ordered stages and generate the first precise map of genomic structural variation, to our knowledge. The occurrence rapidity was estimated on average to be ~7 insertions and ~15 deletions per Myr. Relatively fewer deletions than insertions result in an increased repeat density that causes the observed growth of chloroplast genome sizes. Genome-wide scanning identified 14 positively selected genes that are relevant to photosynthesis system, eight of which were found independently in shade-tolerant or sun-loving rice species. seemed positively selected in both shade-tolerant and sun-loving rice species. The results show that adaptive evolution of chloroplast genes makes rice species adapt to diverse ecological habitats related to sunlight preferences.