The Control of Arabidopsis thaliana Growth by Cell Proliferation and Endoreplication Requires the F-Box Protein FBL17

Abstract

A key step of the cell cycle is the entry into the DNA replication phase that typically commits cells to divide. However, little is known about the molecular mechanisms regulating this transition in plants. Here, we investigated the function of FBL17 (F BOX-LIKE17), an Arabidopsis thaliana F-box protein previously shown to govern the progression through the second mitosis during pollen development. Our work reveals that FBL17 function is not restricted to gametogenesis. FBL17 transcripts accumulate in both proliferating and postmitotic cell types of Arabidopsis plants. Loss of FBL17 function drastically reduces plant growth by altering cell division activity in both shoot and root apical meristems. In fbl17 mutant plants, DNA replication is severely impaired and endoreplication is fully suppressed. At the molecular level, lack of FBL17 increases the stability of the CDK (CYCLIN-DEPENDENT KINASE) inhibitor KIP-RELATED PROTEIN2 known to switch off CDKA;1 kinase activity. Despite the strong inhibition of cell proliferation in fbl17, some cells are still able to enter S phase and eventually to divide, but they exhibit a strong DNA damage response and often missegregate chromosomes. Altogether, these data indicate that the F-box protein FBL17 acts as a master cell cycle regulator during the diploid sporophyte phase of the plant.

SIAMESE-RELATED1 Is Regulated Posttranslationally and Participates in Repression of Leaf Growth under Moderate Drought

“…S construct in the fbl17 mutant background and selected 8-day-old fbl17 321 mutants as explained in Noir et al, 2015. Surprisingly, the SMR1-GFP protein was 322 not stabilized in fbl17, but was almost completely degraded ( Figure S9).…”

“…We have previously shown (Noir et al, 2015) that the Arabidopsis 316 FBL17 protein plays an important role in leaf development and cell division and is 317 involved in the degradation of the CKI KRP2. Since the fbl17 phenotype resembles 318 that of seedlings strongly accumulating SMR1-GFP, FBL17 is a candidate F-box 319 protein that may direct SMR1 degradation.…”

“…As illustrated by the higher-order 591 krp mutants and the smr2 mutant with larger shoots (Cheng et al, 2013;Kumar et 592 al., 2015), CKI proteins restrict cell proliferation during leaf growth even under non-593 stress conditions. SMR1 is also expressed under non-stress conditions and 594 participates in the regulation of leaf and root growth, since smr1 mutants show a 595 slight increase in leaf area and root length, which is most pronounced at the cellular 596 De Veylder et al, 2001;Weinl et al, 2005;Churchman et al, 2006;Liu et al, 601 2008;Jun et al, 2013;Noir et al, 2015). An even stronger growth inhibitory 602 phenotype is observed when plants express a more stable form of SMR1.…”

“…This suggests that additional motif(s) 622 necessary for SMR1 degradation are also present in the C-terminal part of the 623 protein. Finally, based on the resemblance in phenotype between the mutant of 624 FBL17 (the F-box targeting KRP2 protein for degradation (Noir et al, 2015)) and the 625 SMR1-stabilizing plants, we speculated that FBL17 would be a suitable candidate F-626 box protein to target SMR1 for degradation, but this was not the case. Another 627 candidate CRL-type E3 ubiquitin-ligase is SCF SKP2b , which is involved in KRP1 628 degradation (Ren et al, 2008 progression.…”

The Arabidopsis RING-Type E3 Ligase TEAR1 Controls Leaf Development by Targeting the TIE1 Transcriptional Repressor for Degradation

“…The ubiquitin (Ub)-proteasome system is a major protein degradation system that flexibly regulates the activity of transcription regulators and is important in hormone, stress, and other signaling pathways (Potuschak et al, 2003;Chen and Hellmann, 2013;Duplan and Rivas, 2014;Shabek and Zheng, 2014;Noir et al, 2015). Plants utilize the Ub-proteasome system for morphological plasticity and altering physiological states in response to internal and external stimuli via the rapidly changing proteome (Chen and Hellmann, 2013).…”