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. 2016 Aug 6;35(19):2068–2086. doi: 10.15252/embj.201593083

Figure 8. Division of labor model of the regulation of cell proliferation and DNA damage response in Arabidopsis .

Figure 8

DNA damage, for example induced by chemical mutagens, is followed by the activation of the checkpoint kinase ATM (ataxia‐telangiectasia mutated) that activates the transcription factor SOG1 (SUPPRESSOR OF GAMMA RESPONSE 1). On the one hand, SOG1 represses, directly or indirectly, the expression CDKB2 and possible other CDKs as the major driving force of mitosis to allow a cell time for DNA repair. On the other hand, SOG1 directly binds to the promoter of CYCB1;1 and activates its expression. CYCB1;1 builds an active complex together with CDKB1. This complex phosphorylates the DNA binding protein RAD51 (RADIATION SENSITIVE 1) that gets recruited to the DNA damage site. This cascade is required for HR in S and G2 phases of the cell cycle in meristematic cells. To trigger this response, the action of all four B1‐type cyclins is necessary, possibly by providing a threshold of mitotic CDK activity that then gets amplified through SOG1‐dependent stimulation of CYCB1;1 expression.