The Regulatory Mechanism Of Vegetative Phase Change By CDC73 In Arabidopsis Thaliana

Plant life cycle can be divided into an embryonic,a juvenile,an adult,and a reproductive phase.The process of the juvenile to adult transition is referred to as vegetative phase change.Here,we used the model plant,Arabidopsis thaliana,to study the molecular mechanism of vegetative phase change.It is of great theoretical and practical significance to study the mechanism of vegetative phase change because this process regulates a series of economically and agronomically important traits,such as plant biomass,biosynthesis of the secondary metabolite,tiller number,biotic/abiotic response,adventitious root production,etc.All these traits are key determinants of crop yield and quality.The adult leaves usually can be distinguished from juvenile leaves by morphological difference: adult leaves are usually associated with the production of abaxial trichomes,elongated leave shape,increased degree of leaf margin serration.Here,we used the candidate gene method to study the function of Arabidopsis Paf1(Polymerase-ssociated factor 1)complex component CDC73(Cell Division Cycle 73)in regulating vegetative phase change in Arabidopsis thaliana.Compared with that in yeast and animal,CDC73 is only shown to be involved in the regulation of flowering in Arabidopsis,whether it is involved in the regulation of vegetative phase change in Arabidopsis remains unknown.Under short-day conditions,we characterized the phenotype of CDC73 T-DNA insertional mutants(cdc73)and over-expressing plants,and studied the molecular mechanism of CDC73 to regulate vegetative phase change in Arabidopsis using molecular and genetic approaches.The main results are as follows:1.Compared with wild type(Col-0),cdc73 exhibited an accelerated vegetative phase change phenotype,implying that CDC73 functions to delay the juvenile-to-adult transition.cdc73 plants produced significantly earlier abaxial trichomes,elongated leaves,and increased leaf margin serration.In contrast,plants overexpressing CDC73 had no significant effect on vegetative phase change.Loss-of-function mutations in other components of the Paf1 complex did not exhibit any obvious vegetative phase change phenotype,suggesting that other components of the complex might not be involved in vegetative phase change in Arabidopsis thaliana;2.GUS staining of a CDC73 transcriptional reporter,p CDC73::GUS,indicated that CDC73 was mainly expressed in the shoot apical meristem and upper part of the hypocotyl of Arabidopsis thaliana;3.Quantitative analysis of gene expression indicated that mi R156,pri-miRNA156 A and pri-miRNA156 C were significantly down-regulated in cdc73 compared with those in wild type,while miRNA172 was significantly up-regulated.This suggests that CDC73 is involved in the miRNA156-SPL pathway by regulating pri-miRNA156 A and pri-miRNA156 C expression;4.Yeast two-hybrid experiment indicated that there was no physical interaction between CDC73 and the histone H3K4me3 methyltransferase ATXR7 at the protein level.Genetic analysis between CDC73 and ATXR7 suggests that they act in the same genetic pathway;In conclusion,CDC73 functions to delay vegetative phase change by promoting the transcription of pri-miRNA156 A and pri-miRNA156 C,thus increasing the level of mi R156.How CDC73 functions to promote the expression of pri-miRNA156 A and pri-miRNA156 C remains to be explored in the future.