RESUMO
Genome integrity is continuously threatened by external stresses and endogenous hazards such as DNA replication errors and reactive oxygen species. The DNA damage checkpoint in metazoans ensures genome integrity by delaying cell-cycle progression to repair damaged DNA or by inducing apoptosis. ATM and ATR (ataxia-telangiectasia-mutated and -Rad3-related) are sensor kinases that relay the damage signal to transducer kinases Chk1 and Chk2 and to downstream cell-cycle regulators. Plants also possess ATM and ATR orthologs but lack obvious counterparts of downstream regulators. Instead, the plant-specific transcription factor SOG1 (suppressor of gamma response 1) plays a central role in the transmission of signals from both ATM and ATR kinases. Here we show that in Arabidopsis, endoreduplication is induced by DNA double-strand breaks (DSBs), but not directly by DNA replication stress. When root or sepal cells, or undifferentiated suspension cells, were treated with DSB inducers, they displayed increased cell size and DNA ploidy. We found that the ATM-SOG1 and ATR-SOG1 pathways both transmit DSB-derived signals and that either one suffices for endocycle induction. These signaling pathways govern the expression of distinct sets of cell-cycle regulators, such as cyclin-dependent kinases and their suppressors. Our results demonstrate that Arabidopsis undergoes a programmed endoreduplicative response to DSBs, suggesting that plants have evolved a distinct strategy to sustain growth under genotoxic stress.
Assuntos
Arabidopsis/genética , Quebras de DNA de Cadeia Dupla/efeitos dos fármacos , Dano ao DNA , Replicação do DNA/efeitos dos fármacos , DNA de Plantas/genética , Arabidopsis/citologia , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Proteínas Mutadas de Ataxia Telangiectasia , Bleomicina/toxicidade , Proteínas de Ciclo Celular/genética , Células Cultivadas , Cisplatino/toxicidade , Quebras de DNA de Cadeia Dupla/efeitos da radiação , Replicação do DNA/efeitos da radiação , Raios gama , Perfilação da Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Regulação da Expressão Gênica no Desenvolvimento/efeitos da radiação , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Metanossulfonato de Metila/toxicidade , Mutagênicos/toxicidade , Mutação , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Ploidias , Proteínas Serina-Treonina Quinases/genética , Transdução de Sinais/genética , Fatores de Transcrição/genética , Raios UltravioletaRESUMO
Endoreduplication involves a doubling of chromosomal DNA without corresponding cell division. In plants, many cell types transit from the mitotic cycle to the endoreduplication cycle or endocycle, and this transition is often coupled with the initiation of cell expansion and differentiation. Although a number of cell cycle regulators implicated in endocycle onset have been identified, it is still largely unknown how this transition is developmentally regulated at the whole organ level. Here, we report that a nuclear-localized SUMO E3 ligase, HIGH PLOIDY2 (HPY2), functions as a repressor of endocycle onset in Arabidopsis thaliana meristems. Loss of HPY2 results in a premature transition from the mitotic cycle to the endocycle, leading to severe dwarfism with defective meristems. HPY2 possesses an SP-RING domain characteristic of MMS21-type SUMO E3 ligases, and we show that the conserved residues within this domain are required for the in vivo and in vitro function of HPY2. HPY2 is predominantly expressed in proliferating cells of root meristems and it functions downstream of meristem patterning transcription factors PLETHORA1 (PLT1) and PLT2. These results establish that HPY2-mediated sumoylation modulates the cell cycle progression and meristem development in the PLT-dependent signaling pathway.
