OSD1 promotes meiotic progression via APC/C inhibition and forms a regulatory network with TDM and CYCA1;2/TAM

Cell cycle control is modified at meiosis compared to mitosis,because two divisions follow a single dna replication event. cyclin-dependent kinases (cdks) promote progression through both meiosis and mitosis,and a central regulator of their activity is the apc/c (anaphase promoting complex/cyclosome) that is especially required for exit from mitosis. we have shown previously that osd1 is involved in entry into both meiosis i and meiosis ii in arabidopsis thaliana; however,the molecular mechanism by which osd1 controls these transitions has remained unclear. here we show that osd1 promotes meiotic progression through apc/c inhibition. next,we explored the functional relationships between osd1 and the genes known to control meiotic cell cycle transitions in arabidopsis. like osd1,cyca1;2/tam mutation leads to a premature exit from meiosis after the first division,while tdm mutants perform an aberrant third meiotic division after normal meiosis i and ii. remarkably,while tdm is epistatic to tam,osd1 is epistatic to tdm. we further show that the expression of a non-destructible cyca1;2/tam provokes,like tdm,the entry into a third meiotic division. finally,we show that cyca1;2/tam forms an active complex with cdka;1 that can phosphorylate osd1 in vitro. we thus propose that a functional network composed of osd1,cyca1;2/tam,and tdm controls three key steps of meiotic progression,in which osd1 is a meiotic apc/c inhibitor. © 2012 cromer et al.