The phase transition in sweet potato root during tuber differentiationis a complex developmental process that involves changes in gene expression andmorphogenesis. Among the three kinds of root in sweet potato (white fibrousroot, thick-pigmented root and lateral root), ADP-glucose pyrophosphorylase(AGPase) and chalcone synthases (CHS) are expressed only in thick-pigmentedroots after 3 weeks, and this also depends on the developmental stage. Sinceexposing roots to the light or culturing under hydroponic conditions inhibitstuber formation in sweet potato, the expression of AGPase and CHS was studiedunder light and dark conditions. AGPase and CHS expression in sweet potatorootswas suppressed very sensitively by light or water stress, similar to rootdevelopmental patterns. Based on an analysis of AGPase and CHS expression indifferent kinds of root tissues and in different developmental stages, thesegenes were shown to be closely associated with the differentiation ofthickeningpigmented roots.