Chromosome Segregation Defects in Meiosis II

In Arabidopsis, sister chromatid cohesion is maintained by the Shugoshin AtSGO1 in meiosis I, whereas AtSGO2 is not required for protection of cohesion in meiosis and mitosis (Zamariola et al., 2013). Here, we demonstrate that both AtSGOs act redundantly to protect sister chromatid cohesion in meiosis I, and SISHO, a gene with unknown function, is necessary for protection at a later stage, in conjunction with AtSGOs. Furthermore, SISHO is required for appropriate microtubule organization at the end of meiosis I and in meiosis II. This additional role does not seem to be linked to premature loss of sister chromatid cohesion since atsgo1/atsgo2 mutants do not display similar microtubules defects as sisho.

In addition to a function in meiosis, we show that SISHO plays a role in the regulation of mitotic cell division, unlike AtSGOs proteins that seem not required for mitosis. Indeed, we detect growth defects in sisho plants and aneuploidy in sisho somatic cells, suggesting that SISHO mediates sister chromatid cohesion also in mitosis.