Recurrent Plant-Specific Duplications of KNL2 and its Conserved Function as a Kinetochore Assembly Factor

KINETOCHORE NULL2 (KNL2) plays key role in the recognition of centromeres and new CENH3 deposition. To gain insight into the origin and diversification of the KNL2 gene, we reconstructed its evolutionary history in the plant kingdom. Our results indicate that the KNL2 gene in plants underwent three independent ancient duplications in ferns, grasses, and eudicots. Additionally, we demonstrated that previously unclassified KNL2 genes could be divided into two clades alpha KNL2 and beta KNL2 in eudicots and gamma KNL2 and delta KNL2 in grasses, respectively. KNL2s of all clades encode the conserved SANTA domain, but only the alpha KNL2 and gamma KNL2 groups additionally encode the CENPC-k motif. In the more numerous eudicot sequences, signatures of positive selection were found in both alpha KNL2 and beta KNL2 clades, suggesting recent or ongoing adaptation. The confirmed centromeric localization of beta KNL2 and mutant analysis suggests that it participates in loading of new CENH3, similarly to alpha KNL2. A high rate of seed abortion was found in heterozygous beta knl2 plants and the germinated homozygous mutants did not develop beyond the seedling stage. Taken together, our study provides a new understanding of the evolutionary diversification of the plant kinetochore assembly gene KNL2, and suggests that the plant-specific duplicated KNL2 genes are involved in centromere and/or kinetochore assembly for preserving genome stability.

Automated summary

The evolutionary history of the KNL2 gene in plants has been reconstructed, revealing three ancient duplications and differentiation among different plant groups. The study also suggests that the KNL2 gene is involved in centromere and/or kinetochore assembly for preserving genome stability.