SiSTL2 Is Required for Cell Cycle, Leaf Organ Development, Chloroplast Biogenesis, and Has Effects on C Photosynthesis in (L.) P. Beauv.

Deoxycytidine monophosphate deaminase (DCD) is a key enzyme in the dTTP biosynthesis pathway. Previous studies have indicated that DCD plays key roles in the maintenance of the balance of dNTP pools, cell cycle progression, and plant development. However, few studies have elucidated the functions of the DCD gene in Panicoideae plants. has been proposed as an ideal model of Panicoideae grasses, especially for C photosynthesis research. Here, a stripe leaf mutant () was isolated from EMS-induced lines of "Yugu1," the wild-type parent. The mutant exhibited semi-dwarf, striped leaves, abnormal chloroplast ultrastructure, and delayed cell cycle progression compared with Yugu1. High-throughput sequencing and map-based cloning identified the causal gene , which encodes a DCD protein. The occurrence of a single-base G to A substitution in the fifth intron introduced alternative splicing, which led to the early termination of translation. Further physiological and transcriptomic investigation indicated that plays an essential role in the regulation of chloroplast biogenesis, cell cycle, and DNA replication, which suggested that the gene has conserved functions in both foxtail millet and rice. Remarkably, in contrast to DCD mutants in C rice, showed a significant reduction in leaf cell size and affected C photosynthetic capacity in foxtail millet. qPCR showed that had a similar expression pattern to typical C genes in response to a low CO environment. Moreover, the loss of function of resulted in a reduction of leaf C content and the enrichment of DEGs in photosynthetic carbon fixation. Our research provides in-depth knowledge of the role of DCD in the C photosynthesis model and proposed new directions for further study of the function of DCD.