Map-based Cloning And Functional Analysis Of A Stripe Leaf Gene SiSTL2 In Foxtail Millet

Deoxycytidine monophosphate deaminase?dCMP deaminase,DCD?is a key enzyme in the de novo 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.Setaria has been proposed as an ideal model of Panicoideae grasses,especially for C₄ photosynthesis research.Here,a Setaria italica stripe leaf mutant?sistl2?was isolated from EMS-induced lines of‘Yugu1',the wildtype parent.The sistl2 mutant exhibited semi-dwarf,striped leaves,abnormal chloroplast ultrastructure,and delayed cell cycle progression compared with Yugu1.In our study,we surveyed the agriculture traits,photosynthetic parameters,leaf anatomical structure,and chloroplast ultrastructure of sistl2,identified the causal gene SiSTL2 by high-throughput sequencing and map-based cloning,and then analyzed the gene function.The main results of our study are summarized as follows:?1?Morphological observations on sistl2 showed that the plant height,leaf area,panicle length and diameter,and setting percentage were impaired.And the mutant showed phenotypes of stripe leaves,unregular leaf veins and Kranz structure,smaller leaf cells,and undeveloped chloroplasts.?2?sistl2 showed low chlorophyll content and photosynthetic capacity.?3?High-throughput sequencing and map-based cloning identified the causal gene,Seita.9G511200,named SiSTL2,which encodes a DCD protein.The result was verified by complementary assay on the rice mutant of the homolog gene.?4?SiSTL2 encodes a DCD protein,which locates in cytoplasm.The mutation in SiSTL2 led to restraints in dTTP synthesis and chloroplast genes transcription.And SiSTL2 can influence the cell cycle progression under the control of E2F transcription factor.?5?Moreover,the loss of function of SiSTL2 resulted in a reduction of leaf ¹³C content.And SiSTL2 had a similar expression pattern to typical C₄ genes in response to a low CO₂ environment.?6?RNA-seq showed the enrichments of DEGs in photosynthetic carbon fixation,DNA replication,and cellcycle regulation.Our research provides in-depth knowledge of the role of DCD in the C₄ photosynthesis model S.italica and proposed new directions for further study of the function of DCD.