Abstract
Endoreduplication involves a doubling of chromosomal DNA without corresponding cell division. In plants many cell types transit from the mitotic cycle to the endoreduplication cycle or endocycle, and this transition is often coupled with the initiation of cell expansion and differentiation. In spite of the importance of the cell cycle transition, it is still largely unknown how this process is developmentally regulated. We recently found that a SUMO E3 ligase, HIGH PLOIDY2 (HPY2), functions as a repressor of endocycle onset in Arabidopsis meristems. Loss of HPY2 results in a premature transition from the mitotic cycle to the endocycle, leading to severe dwarfism with defective meristems. HPY2 functions as a SUMO E3 ligase in vivo and in vitro through an SP-RING domain characteristic of MMS21-type SUMO E3 ligases. HPY2 is predominantly expressed in proliferating cells of root meristems and acts downstream of meristem patterning transcription factors PLETHORA1 (PLT1) and PLT2. These results establish that HPY2-mediated sumoylation modulates the cell cycle progression and meristem development in the auxin-PLT-dependent signaling pathway.
