ArabidopsisULTRAVIOLET-B-INSENSITIVE4 Maintains Cell Division Activity by Temporal Inhibition of the Anaphase-Promoting Complex/Cyclosome  

Abstract

The anaphase-promoting complex/cyclosome (APC/C) is a multisubunit ubiquitin ligase that regulates progression through the cell cycle by marking key cell division proteins for destruction. To ensure correct cell cycle progression, accurate timing of APC/C activity is important, which is obtained through its association with both activating and inhibitory subunits. However, although the APC/C is highly conserved among eukaryotes, no APC/C inhibitors are known in plants. Recently, we have identified ULTRAVIOLET-B-INSENSITIVE4 (UVI4) as a plant-specific component of the APC/C. Here, we demonstrate that UVI4 uses conserved APC/C interaction motifs to counteract the activity of the CELL CYCLE SWITCH52 A1 (CCS52A1) activator subunit, inhibiting the turnover of the A-type cyclin CYCA2;3. UVI4 is expressed in an S phase-dependent fashion, likely through the action of E2F transcription factors. Correspondingly, uvi4 mutant plants failed to accumulate CYCA2;3 during the S phase and prematurely exited the cell cycle, triggering the onset of the endocycle. We conclude that UVI4 regulates the temporal inactivation of APC/C during DNA replication, allowing CYCA2;3 to accumulate above the level required for entering mitosis, and thereby regulates the meristem size and plant growth rate.

SAMBA, a plant-specific anaphase-promoting complex/cyclosome regulator is involved in early development and A-type cyclin stabilization

“…Recently, APC10 had been shown to regulate the CYCB1;1 abundance (28), and the two APC/ C inhibitors UVI4 and UVI-like/OSD1/GIG1 stabilize CYCA2;3 and CYCB1;2, respectively (22,23). Therefore, we tested whether SAMBA interacts with mitotic cyclins and affect their stability.…”

“…Recently, ULTRAVIOLET-B-INSENSITIVE4 (UVI4) and UVI4-like/OMISSION OF SECOND DIVISION1/GIGAS CELL1 (UVI4/OSD1/GIG1) were identified as plant-specific inhibitors of the APC/C that are required for proper mitotic progression in Arabidopsis (22,23).…”

DELLA Signaling Mediates Stress-Induced Cell Differentiation in Arabidopsis Leaves through Modulation of Anaphase-Promoting Complex/Cyclosome Activity

“…Possibly, this is due to functional redundancy with UVI4. Overexpression of UVI4 is most likely lethal, however (Heyman et al, 2011), so this could not be tested.…”

“…Another major pathway is the control of anaphase-promoting complex/cyclosome (APC/C) activity through its activating CELL CYCLE SWITCH PROTEIN52A (CCS52A) subunits, which positively regulate endoreduplication (Lammens et al, 2008) by targeting mitotic cyclins for destruction (Boudolf et al, 2009;Kasili et al, 2010). Activation of APC/C by CCS52A proteins is counteracted by UVI4 (Hase et al, 2006;Heyman et al, 2011;Iwata et al, 2011). Upstream, the atypical E2F-like protein dimerization partner-E2F-LIKE1/E2Fe (DEL1/E2FE) represses the expression of CCS52A genes, thereby delaying the developmental onset of endoreduplication (Lammens et al, 2008).…”

“…Upstream, the atypical E2F-like protein dimerization partner-E2F-LIKE1/E2Fe (DEL1/E2FE) represses the expression of CCS52A genes, thereby delaying the developmental onset of endoreduplication (Lammens et al, 2008). The regulation of DEL1 transcription is less clear, although recently it was shown that the classical E2Fs E2Fb and E2Fc antagonistically regulate DEL1 transcription, thereby controlling endoreduplication in the hypocotyl in response to light , whereas UVI4 expression is also activated by E2Fa and E2Fb (Heyman et al, 2011). Endoreduplication generally correlates with cell expansion and differentiation, but its physiological role is still under debate and is likely tissue and stimulus specific .…”