FZR2/CCS52A1Expression Is a Determinant of Endoreduplication and Cell Expansion in Arabidopsis    

Abstract

Endoreduplication, a modified cell cycle that allows cells to increase ploidy without subsequent cell division, is a key component of plant growth and development. In this work, we show that some, but not all, of the endoreduplication of Arabidopsis (Arabidopsis thaliana) is mediated by the expression of a WD40 gene, FIZZY-RELATED2 (FZR2). Loss-of-function alleles show reduced endoreduplication and reduced expansion in trichomes and other leaf cells. Misexpression of FZR2 is sufficient to drive ectopic or extra endoreduplication in leaves, roots, and flowers, leading to alteration of cell sizes and, sometimes, organ size and shape. Our data, which suggest that reduced cell size can be compensated by increased cell proliferation to allow normal leaf morphology, are discussed with respect to the so-called compensation mechanism of plant development.

CULLIN 4-RING FINGER-LIGASE plays a key role in the control of endoreplication cycles in Arabidopsis trichomes

“…As recently shown, CCS52 cooperates with SIM to abolish mitotic CDK activity, and we postulate that the function of CCS52 is needed only during the entry phase into an endocycle (31). This is supported by the observation that ccs52a1 mutants have reduced but still significant levels of endoreplication (30). Although SIM overexpression was found only to block mitosis leading to large endoreplicated cells (25), overexpression of KRPs can block S-phase (47,48).…”

“…Mutants in ccs52a1 were found to exhibit only a moderate reduction in endoreplication levels, indicating that reduced APC/C activity is largely compatible with progression of endoreplication cycles (30,31). Initially therefore we tested whether APC/C is active during the endoreplication cycles in trichomes.…”

“…Conversely, overexpression of a N-terminally truncated B-type cyclin, CYCLIN B1;2 (CYCB1;2), or a D-type cyclin, CYCLIN D3;1 (CYCD3;1), gave rise to multicellular trichomes (27)(28)(29). In addition, CCS52A1 has recently been implicated in endoreplication control in trichomes, as ccs52a1 mutants displayed one endoreplication round fewer than WT trichomes and ccs52a1-sim double mutants displayed a strongly enhanced sim mutant phenotype (30,31). These data suggest that the APC/C plays a role in endoreplication control in trichomes.…”

Regulating DNA Replication in Plants

“…In Arabidopsis, homologs of both Cdc20/Fzy and Cdh1/Fzr APC/C activators exist and participate in controlling the onset of endocycles by targeting various cyclins (Gutierrez 2009). The Arabidopsis homolog of Cdh1/Fzr is known as CCS52A (CELL CYCLE SWITCH 52A), and its loss of function produces a reduction in ploidy (Cebolla et al 1999;Larson-Rabin et al 2009). Interestingly, CCS52A is a target of E2FE/DEL1, one of the three atypical E2F encoded in the Arabidopsis genome (Ramirez-Parra et al 2007;Lammens et al 2008) and homolog of the human E2F7-9.…”

Perturbation of cell cycle regulation triggers plant immune response via activation of disease resistance genes

“…Arabidopsis has five CDC20 homologs (CDC20.1-CDC20.5), as well as three CDH1 homologs (CCS52A1/ FZR2, CCS52A2/FZR1, and CCS52B/FZR3). Both CCS52A1 and CCS52A2 reportedly regulate the onset of endoreduplication (4)(5)(6)(7). APC/C activity is essential for cell cycle transition, and total loss of APC/C activity results in lethality.…”