Interaction of CPR5 with cell cycle regulators UVI4 and OSD1 in Arabidopsis.

The impact of cell cycle on plant immunity was indicated by the enhancement of disease resistance with overexpressing OSD1 and UVI4 genes that are negative regulators of cell cycle controller APC (anaphase promoting complex). CPR5 is another gene that is implicated in cell cycle regulation and plant immunity, but its mode of action is not known. Here we report the analysis of genetic requirement for the function of UVI4 and OSD1 in cell cycle progression control and in particular the involvement of CPR5 in this regulation. We show that the APC activator CCS52A1 partially mediates the function of OSD1 and UVI4 in female gametophyte development. We found that the cpr5 mutation suppresses the endoreduplication defect in the uvi4 single mutant and partially rescued the gametophyte development defect in the osd1 uvi4 double mutant while the uvi4 mutation enhances the cpr5 defects in trichome branching and plant disease resistance. In addition, cyclin B1 genes CYCB1;1, CYCB1;2, and CYCB1;4 are upregulated in cpr5. Therefore, CPR5 has a large role in cell cycle regulation and this role has a complex interaction with that of UVI4 and OSD1. This study further indicates an intrinsic link between plant defense responses and cell cycle progression.