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. 2012 Sep 1;7(9):1079-81.
doi: 10.4161/psb.21133. Epub 2012 Aug 17.

Roles of GIG1 and UVI4 in genome duplication in Arabidopsis thaliana

Eriko Iwata  1 , Saki Ikeda, Natsumi Abe, Asuka Kobayashi, Mariko Kurata, Sachihiro Matsunaga, Yasushi Yoshioka, Marie-Claire Criqui, Pascal Genschik, Masaki Ito
Affiliations

Roles of GIG1 and UVI4 in genome duplication in Arabidopsis thaliana

Eriko Iwata et al. Plant Signal Behav. .

Abstract

Endomitosis and endoreplication are atypical modes of cell cycle that results in genome duplication in single nucleus. Because the cell size of given cell type is generally proportional to the nuclear DNA content, endoreplication and endomitosis are effective strategy of cell growth, which are widespread in multicellular organisms, especially those in plant kingdom. We found that these processes might be differently regulated by GIGAS CELL1 (GIG1) and its paralog UV-INSENSITIVE4 (UVI4) in Arabidopsis thaliana. GIG1 and UVI4 may negatively regulate activities of anaphase-promoting complex or cyclosome (APC/C) ubiquitin ligase that acts as an important mitotic regulator. The gig1 mutation induced ectopic occurrence of endomitosis during somatic cell division, while it has been reported that uvi4 mutation resulted in premature occurrence of endoreplication during organ development. Overexpression of GIG1 and UVI4 dramatically increased the amount of mitotic cyclin, CYCB1;1, a well-known substrate of APC/C. Ectopic endomitosis in gig1 was enhanced by mutation in CYCB2;2 and suppressed by downregulation of APC10 encoding a core subunit of APC/C. Overexpression of CDC20.1, an activator protein of APC/C, further promoted the ectopic endomitosis in gig1. These findings suggest that endomitosis and endoreplication are regulated by similar molecular mechanisms, in which two related proteins, GIG1 and UVI4, may inhibit APC/C in different ways.

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Figures

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Figure 1.gig1 phenotype is variously affected by genetic manipulations of MYB3R4, CYCB2;2, CDC20 and APC10. (A) Quantitative analysis of gigas cell phenotype in various genetic backgrounds. Seedlings at 7 d were cleared and observed with differential interference contrast microscopy to count the number of gigas cells in abaxial epidermis of one cotyledon. (B-E) Fluorescent images were taken for abaxial epidermis of cotyledons from 5 d-old seedlings with the indicated genetic backgrounds. GFP fluorescence of proTMM:GUS-GFP marker, specific to stomatal lineage cells, is shown in green color. CDC20.1OE represents overexpression construct of CDC20.1 that is driven by promoter from EPF2 gene (proEPF2:CDC20.1), whereas APC10KD represents APC10 knockdown that was caused by pro35S:APC10-mediated co-suppression.
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Figure 2. Overexpression of GIG1 causes accumulation of CYCB1;1-GUS. Seedlings were grown for 6 d in the absence (A) or presence (B) of 10 μM DEX, and were stained with X-Gluc.
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