A CDKB/KRP/FB3 cell cycle core complex functions in rice gametes and zygotes

Abstract

The cell cycle controls division and proliferation of all eukaryotic cells and is tightly regulated at multiple checkpoints by complexes of core cell cycle proteins. Due to the difficulty in accessing female gametes and zygotes of flowering plants, little is known about the molecular mechanisms underlying initiation embryogenesis despite the crucial importance of this process for seed crops. In this study, we reveal four levels of factors involved in rice zygotic cell cycle control and characterize their functions and regulation. Protein-protein interaction studies, including within zygote cells, and in vitro biochemical analyses delineate a model of the zygotic cell cycle core complex for rice. In this model, CDKB1, a major regulator of plant mitosis, is a cyclin (CYCD5)-dependent kinase; its activity is coordinately inhibited by two cell cycle inhibitors, KRP4 and KRP5; and both KRPs are regulated via F-box protein 3 (FB3)-mediated proteolysis. Supporting their critical role in controlling the rice zygotic cell cycle, mutations in KRP4, KRP5, and FB3 result in the compromised function of sperm cells and abnormal organization of female germ units, embryo and endosperm, thus significantly reducing seed-set rates. This work helps reveal regulatory mechanisms controlling the zygotic cell cycle toward seed formation in angiosperms.

Cell cycle‐dependent kinase inhibitor GhKRP6, a direct target of GhBES1.4, participates in BR regulation of cell expansion in cotton

“…In prior studies, ICK or KRP was typically studied as a type A or type B CDK inhibitor (Wang et al., 1998; Xu et al., 2022). The major drivers of the plant cell cycle, A‐type CDKs control the G1‐S and G2‐M transition points in the cell cycle, while CDKB is plant specific and accumulates in a cell cycle phase‐dependent manner, reaching its highest level during G2‐M transition (Boudolf et al., 2006; Dewitte & Murray, 2003).…”