In living organisms cells divide and reproduce in two ways, mitosis and meiosis. Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells.
During mitotic and meiotic cell divisions, the spindle fibers bind chromosomes via a special region called centromere to pull sister chromatids apart. The centromere consists of centromeric DNA and a multi-protein complex, the kinetochore.
The kinetochore ensures the correct segregation (distribution) of the chromosomes between the two daughter cells and hence maintains genome stability in eukaryotic organisms.
In plants, defects in centromere (kinetochore) function often result in the formation of cells with an abnormal number of chromosomes (poly- and/or aneuploidy) leading to abnormal plant development. In animals and human, defects in centromere (kinetochore) function result either in apoptosis and cell death or in initiation and progression of cancer as well as in various genetic disorders.
The histone CenH3 is essential for the formation and function of the kinetochore. It is incorporated into the centromere in a multi-step process which is largely determined by a specific protein, called KINETOCHORE NULL2 (KNL2), in addition to several other factors.
By manipulating KNL2, it has already been possible to produce double haploids in the model plant Arabidopsis thaliana. This is very important because it makes it possible to generate homozygous lines in only one generation instead of five or more, as has usually been the case in conventional breeding.
To gain insight into the origin and diversification of the KNL2 gene, an international team of scientists led by the IPK Leibniz Institute reconstructed its evolutionary history in the plant kingdom. "Our results indicate that the KNL2 gene in plants has undergone three independent ancient duplications in ferns, grasses and eudicotyledons," said Dr. Inna Lermontova, head of the Kinetochore Biology research group at IPK. "In addition, we were able to show that previously unclassified KNL2 genes can be divided into two groupes: αKNL2 and βKNL2 in eudicotyledons, and γKNL2 and δKNL2 in grasses."
“We also confirmed that the recently identified βKNL2 variant of Arabidopsis plays a role in centromeric localisation of CenH3 and in control of cell division as it has been shown for the αKNL2 variant. We therefore consider a βKNL2 as a new candidate for use in haploid induction approaches.”
Overall, the study provides a new understanding of the evolutionary diversification of the KNL2 gene and suggests that plant-specific duplicated KNL2 genes have a significant impact on the centromere and kinetochore and are thus also involved in the maintenance of genome stability.
Molecular Biology and Evolution
Recurrent Plant-Specific Duplications of KNL2 and Its Conserved Function as a Kinetochore Assembly Factor
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