AUXIN BINDING PROTEIN1(ABP1)has long been proposed as a candidate of auxin receptor to mediate auxin action in plants,including early auxin response at the plasma membrane,cell division and expansion,and auxin regulated gene expression.It is important throughout the life of plants,such as embryogenesis and postembryonic shoot and root development.However,the function of ABP1 in the development of ramie(Boehmeria nivea L.)remains unclear.Here,we examined the role of the ABP1 gene in the development of shoot in ramie,especially in leaf venation ontogeny,by transforming ABP1 antisense construct into the plants.We showed that ABP1 expression was repressed in ABP1 antisense transgenic plantlets.The suppression of ABP1 expression led to defects in plant growth including dwarf plant,and decreased apical dominance in the intact plant.In addition,ABP1 antisense lines exhibited a serious retard of leaf development involving small and twisted leaves,sparse trichomes,and a decreased cell expansion.Moreover,ABP1 antisense lines developed an incomplete leaf venation,which became smaller and lacked in some leaf tissues.Though the cell arrangement was normal in midrib and lateral vein,cell size was decrease and some cell layers were missing in midrib.The abnormal phenotype of leaf venation was attributed to the decrease in cell number and cell size.Our data support that ABP1 is necessary for shoot growth in ramie.More importantly,it plays a key role for the development of ramie leaf venation by regulating both cell expansion and division.