Expression and protein localization analyses of Arabidopsis GLABRA3 (GL3) in tomato (Solanum lycopersicum) root epidermis

Abstract

The arrangement of root hair and non-hair cells in the root epidermis provides a useful model for understanding the cell fate determination system in plants. A network of related transcription factors, including GLABRA3 (GL3), influences the patterning of cell types in Arabidopsis. GL3 is expressed primarily in root hair cells and encodes a bHLH transcription factor, which inhibits root hair differentiation in Arabidopsis root epidermis. By transforming the GL3 promoter::GFP into tomato, we demonstrated that the Arabidopsis GL3 promoter can function in tomato root epidermis. GFP fluorescence was observed in almost all root epidermal cells in the GL3::GFP transgenic tomato plants, indicating that all root epidermal cells of tomato possess root hair cell identity similar to that of Arabidopsis root hair cells. This is consistent with the phenotype of the tomato root, in which all epidermal cells produce root hairs. Moreover, we observed the localization of a GL3:GFP fusion protein in GL3::GL3:GFP transgenic tomato; although GL3 is known to exclusively localize in non-hair cell nuclei in Arabidopsis root epidermis, GL3:GFP fluorescence was detected not in the nuclei but in the cytoplasm of transgenic tomato epidermal cells. These results suggest that the nuclear localization mechanism differs between tomato and Arabidopsis.