Primary Study On The Boundary Formation Of Lateral Organs In Lotus Japonicus

1 Primary study on the boundary formation of lateral organs in Lotus japonicusThe morphology of leaf varies dramatically in different species, which is evolutionally and economically important. Leaf development has made good advances in the last decade. It has been uncovered that several key developmental progresses are involved in the leaf development. For example, the recruitment of founder cells, the determination of identities and the elongation and differentiation of leaf primordia. The compound leaf development also gets some advance from two model systems, tomato and pea. However, the boundary formation between leaflets is less to be known in the compound leaf development after the meristem centers form directed by the meristem identity genes.We explore the question in Legume model system Lotus japonicus. Two types of mutants, which have defect in the boundary formation between leaflets, were analyzed. The first type of mutant, ful1, show the specific fusion between the upper three leaflets. While the second type of mutant, uml, show more general fusion of lateral organs, including the leaflet fusion.Genetic analysis showed that the phenotype of ful1 is controlled by a single recessive nuclear locus. The initiation of leaflet primordial in ful1 mutants is similar with that of wild types through SEM study. It suggests that the abnormality occurs after the P3 stage. The SEM data show that the boundary formation between the lateral leaflets and the terminal leaflet in ful1 mutants is remarkably slower than that of wild type after the five leaflets initiate from the common primordia of compound leaves. We cloned this gene by the map-based cloning approach, combining the comparative genome research. The sequencing result indicates that a C to T switching in the CDS of LjCUC1 resulted in a conserved P66 to S switching in ful1-1 mutants; and also a C to T switching in the CDS of LjCUC1 resulted in an ahead of schedule translation stop codon thus made the ful1-2 a null mutant, which match well with the result of allelic tests. The transcripts of LjCUC1 can be detected in the boundary region between leaflets and lateral organs through RNA in situ hybridization. These results strongly suggest the phenotype of ful1 mutants is caused by the mutation of the LjCUC1 gene, which encodes a putative NAC (NAM/ATAF1,2/CUC2) domain...