In a study published in BMC Plant Biology, researchers have discovered pervasive degradation and repeated complete loss of a key set of plastid genes in the widespread genus Cymbidium.
The research focused on the Cymbidium genus, renowned for its varied life forms—from tree-dwelling epiphytes to ground-growing terrestrials—and its evolutionary shift toward mycoheterotrophy, a mode of deriving nutrients from fungi. This makes it an ideal natural laboratory for studying the interplay between ecological adaptation and genomic change.
By analyzing complete plastid genomes and nuclear DNA data from 56 species—representing about 90% of known Cymbidium species—the researchers employed advanced evolutionary tools to trace genomic changes. They identified four distinct types of plastome structure, with repeated DNA region contractions linked to the loss of the ndhF gene, especially prevalent in terrestrial lineages.
Central to the study was the fate of the ndh gene family, crucial for photosynthetic function. Analysis revealed that while these genes were functional in the ancestor of all Cymbidium, they have undergone progressive degeneration across both epiphytic and terrestrial evolutionary lines. Notably, the fully mycoheterotrophic, leafless species Cymbidium macrorhizon still retains four ndh genes, indicating its recent evolutionary shift (around 2.5 million years ago) and a delayed genomic degradation.
Evolutionary pressure analysis showed relaxed selection on some plastid genes and intensified selection on others, particularly within the ndh group. While some phylogenetic signals conflicted between plastid and nuclear genomes, ancestral reconstruction consistently supported the overall evolutionary narrative.
By integrating comparative genomics, this study systematically reveals the multiple drivers of plastome evolution in Cymbidium, highlighting the roles of photoprotective needs, photosynthetic pathway shifts, and mycorrhizal dependence.
" The work not only deepens our understanding of diversification in Cymbidium but also provides new empirical evidence on early genomic signatures in plant heterotrophic evolution,” said YU Wenbin of XTBG.
Contact
YU Wenbin Ph.D Principal Investigator
Xishuangbanna Tropical Botanical Garden
E-mail:yuwenbin@xtbg.ac.cn
Published: 22 December 2025
