Biological Function Analysis Of HEADLESS From WOX Family In Medicago Truncatula

The growth of plants needs the normal development of shoot apex meristem and floral meristems.The studies in Arabidopsis thaliana show that WUSCHEL(WUS)gene is mainly involved in the maintenance of stem cells,which plays an important role in the development of ovule and pollen as well.WUS can regulate meristems by inducing cytokinin response regulators,and can also form a negative feedback regulatory loops with CLAVATA(CLV)to determine the dynamic balance between stem cell division and cell differentiation.Also WUS can interact with AGAMOUS(AG)gene to regulate the exchange of flower meristems to floral organs.However,there is no clear research on how this gene regulates and affects the maintenance and development of stem cells in legumes.Medicago truncatula is a model organism for the study of functional genomics in legumes.Its genome is small,and its genetic transformation system is relatively mature.We successfully cloned the HDL gene based on three headless(hdl)mutants with the abnormal shoot apical meristem.By analyzing the phenotype of the hdl-1 mutant and the function of HDL gene,we preliminary clear the role of HDL gene in shoot apical meristem regulation and leaf development.The main findings are as follows:Using forward genetic approaches,we identified that HDL,a homologue of Arabidopsis WUSCHEL,is required for M.truncatula SAM maintenance and leaf development.Disruption of HDL led to disorganized specification and arrest of the SAM and axillary meristems resulting in the hdl mutant being locked in the vegetative phase without apparent stem elongation.hdl mutant leaves are shorter in the proximal-distal axis due to reduced tip elongation,which lead to higher blade width/length ratio and altered leaf shape,uncovering novel phenotypes undescribed in the Arabidopsis wus mutant.HDL functions as a transcriptional repressor by recruiting TOPLESS(TPL)through its conserved WUS-box and EAR-like motif.Further genetic analysis revealed that HDL and STENOFOLIA(STF),a key regulator of M.truncatula lamina outgrowth,acted independently in leaf development although HDL could recruit TPL in the same manner as STF does.Our results indicate that HDL performs conserved and novel functions in regulating shoot meristems and leaf shape in M.truncatula,which provide new avenues for understanding meristem biology and plant development.