ALR encoding dCMP deaminase is critical for DNA damage repair, cell cycle progression and plant development in rice

: Deoxycytidine monophosphate deaminase (dCMP deaminase, DCD) is crucial to the production of dTTP needed for DNA replication and damage repair. However, the effect of DCD deficiency and its molecular mechanism are poorly understood in plants. Here, we isolated and characterized a rice albinic leaf and growth retardation (alr) mutant that is manifested by albinic leaves, dwarf stature and necrotic lesions. Map-based cloning and complementation revealed that ALR encodes a DCD protein. OsDCD was expressed ubiquitously in all tissues. Enzyme activity assays showed that OsDCD catalyses conversion of dCMP to dUMP, and the ΔDCD protein in the alr mutant is a loss-of-function protein that lacks binding ability. We report that alr plants have typical DCD-mediated imbalanced dNTP pools with decreased dTTP; exogenous dTTP recovers the wild-type phenotype. A comet assay and Trypan Blue staining showed that OsDCD deficiency causes accumulation of DNA damage in the alr mutant, sometimes leading to cell apoptosis. Moreover, OsDCD deficiency triggered cell cycle checkpoints and arrested cell progression at the G1/S-phase. The expression of nuclear and plastid genome replication genes was down-regulated under decreased dTTP, and together with decreased cell proliferation and defective chloroplast development in the alr mutant this demonstrated the molecular and physiological roles of DCD-mediated dNTP pool balance in plant development.