Genetic Framework of Cyclin-Dependent Kinase Function in Arabidopsis

Abstract

Cyclin-dependent kinases (CDKs) are at the heart of eukaryotic cell-cycle control. The yeast Cdc2/CDC28 PSTAIRE kinase and its orthologs such as the mammalian Cdk1 have been found to be indispensable for cell-cycle progression in all eukaryotes investigated so far. CDKA;1 is the only PSTAIRE kinase in the flowering plant Arabidopsis and can rescue Cdc2/CDC28 mutants. Here, we show that cdka;1 null mutants are viable but display specific cell-cycle and developmental defects, e.g., in S phase entry and stem cell maintenance. We unravel that the crucial function of CDKA;1 is the control of the plant Retinoblastoma homolog RBR1 and that codepletion of RBR1 and CDKA;1 rescued most defects of cdka;1 mutants. Our work further revealed a basic cell-cycle control system relying on two plant-specific B1-type CDKs, and the triple cdk mutants displayed an early germline arrest. Taken together, our data indicate divergent functional differentiation of Cdc2-type kinases during eukaryote evolution.

The plant‐specific CDKB 1‐ CYCB 1 complex mediates homologous recombination repair in Arabidopsis

“…Among the five CDKs in Arabidopsis that have been implicated in direct regulation of cell‐cycle progression (i.e. CDKA;1, CDKB1;1, CDKB1;2; CDKB2;1, and CDKB2;2), CDKA;1 has been found to be of central importance controlling both the G1‐S and G2‐M transition (Nowack et al , 2012). Although homozygous cdka;1 mutants exist, they are so severely compromised that an analysis, especially under stress conditions, faces the danger of giving ambiguous results due to pleiotropic and indirect effects (Nowack et al , 2012).…”

“…CDKA;1, CDKB1;1, CDKB1;2; CDKB2;1, and CDKB2;2), CDKA;1 has been found to be of central importance controlling both the G1‐S and G2‐M transition (Nowack et al , 2012). Although homozygous cdka;1 mutants exist, they are so severely compromised that an analysis, especially under stress conditions, faces the danger of giving ambiguous results due to pleiotropic and indirect effects (Nowack et al , 2012). We therefore made use of a previously described weak loss‐of‐function allele, designated CDKA;1 T14D;Y15E or short DE (Dissmeyer et al , 2009), to address whether CDKA;1 plays a role in the response to cisplatin.…”

“…In addition, it was shown that CYCB1;2 has kinase activity in complex with CDKB1s in vitro (Harashima & Schnittger, 2012). Since CDKB1;1 and CDKB1;2 were found to have overlapping functions (Xie et al , 2010; Cruz‐Ramirez et al , 2012; Nowack et al , 2012; Weimer et al , 2012), we used the previously generated double mutant cdkb1;1 cdkb1;2 in the following studies, referred to as cdkb1 . We first tested cdkb1 mutants on HU but the single as well as the double mutants grew indistinguishably from the wild type (Fig 4D, E and K).…”

“…Arabidopsis has only one Cdk1/Cdk2 homolog, namely CDKA;1, which also contains functional aspects of both CDKs in metazoans, that is, CDKA;1 function in S and M phase control (Nowack et al , 2012). Here, we have shown that plants with a reduced activity level of CDKA;1 are neither hypersensitive to BLM nor cisplatin.…”

“…However, due to the lack of mutants, a detailed analysis of B2‐type kinases is still pending. In contrast, B1‐type CDKs have been functionally analyzed, but these studies revealed so far that they apparently act as axillary kinases to A1‐type kinases contributing to the refinement of developmental decisions (Xie et al , 2010; Cruz‐Ramirez et al , 2012; Nowack et al , 2012; Weimer et al , 2012). …”