Phytohormones in regulation of the cell division and endoreduplication process in the plant cell cycle†
The present review suggests the significance of various phytohormones in the regulation of cell division and the endoreduplication process in plant cells. Here, molecular pathways are designed that clearly elucidate the role of phytohormones in the regulation of the cell division and endoreduplication process. This determines the stages at which the cell division cycle diverts towards the endoreduplication process. Phytohormones manage the activity of CDK/CYC complexes and RBR proteins at various stages of the cell cycle by controlling the transcription and destruction of E2F proteins. For example, cytokinin stimulates the G1 phase by activating the CDKA/CYCD complex, ABA regulates the activity of CDKA in the G1 and G2 phase using CDK inhibitor proteins, GA stimulates activation of CDK/CYC complexes using CAKs, auxin regulates the progress of the cell cycle from the G1/S transition to the G2/M transition, JA regulates the signaling of GA using DELLA proteins and ethylene regulates the activity of CDK B. Hyperphosphorylation or hypophosphorylation of RBR protein by the CDK/CYC complex will determine whether the cell cycle shifts towards cell division or endoreduplication. The activity of the E2F transcription factors is most significant during these processes, which is in turn regulated by phytohormones. Accumulation of E2F A in the G1 phase will drive the cell cycle towards the S phase. E2FB will give a signal to the mitotic inducing factor CDKB/CYCD complex, which will lead the cell cycle towards mitosis. E2FB is a key target of auxin, in determining whether the cell with undergo mitosis or endoreduplication. Auxin also regulates the activity of E2FC using a RUB–cullin signaling pathway, whose over-expression leads the cell cycle towards the endocycling process.