Root architecture has become a model for studying developmental plasticity.Recent identification of the Arabidopsis SUMO E3 ligase SR1 is necessary for primary root meristem development.However,the developmental mechanism regulating the process and its role during the elaboration of root system architecture is poorly understood.Here,we show that SR1 plays an essential role in the development of both primary root meristem and lateral roots as well as vascular development.pSR1:SR1:GUS gene-reporter fusions in transgenic roots establish the spatial expression of SR1 in primary root meristem,lateral root and root vasculature.Mutation of SR1 leads to stunted roots with defective meristems,less lateral roots and the cell numbers in the vascular system are markedly reduced.