Accurate chromosome segregation is essential for cell division and plant reproduction. During cell division, cells must carefully control the transition from metaphase, when chromosomes are aligned, to anaphase, when chromosomes begin to separate.
A key regulator of this transition is Cell Division Cycle 20 (CDC20), which activates the anaphase-promoting complex/cyclosome (APC/C). Although CDC20 is well known as a cell-cycle regulator, plants often contain multiple CDC20 genes, and how these genes work together during mitosis and meiosis remains poorly understood.
Researchers from Yangzhou University and collaborating institutions used CRISPR/Cas9 to generate a series of mutants affecting the three CDC20 genes in rice. The study showed that the three rice CDC20 genes function redundantly in cell-cycle progression. When CDC20 activity was severely disrupted, gametophytic mitosis was impaired, leading to gametophyte lethality. This finding demonstrates that CDC20 is essential for mitotic progression in rice.
They also identified mutant alleles that retained normal mitotic development but caused defects during meiosis. Two mutants, cdc20-triple-1 and cdc20-triple-2 , arrested at metaphase I and failed to enter anaphase I normally, despite having normal chromosome alignment. In contrast, cdc20-triple-3 and cdc20-triple-4 completed meiosis I but showed defects during the second meiotic division, including abnormal chromosome segregation.
The different mutant phenotypes reveal that CDC20 activity is required at distinct stages of meiotic progression. Analysis of chromosome cohesion and SGO1 dynamics further provided clues to the relationship between CDC20-dependent cell-cycle progression and chromosome cohesion during meiosis.
Together, these findings establish CDC20 as a central regulator of the metaphase-to-anaphase transition in both mitosis and meiosis in rice. They also show how an allelic series can reveal stage-specific requirements for an essential cell-cycle regulator.
Science China Life Sciences