A soybean lectin-GFP fusion labels the vacuoles in developing Arabidopsis thaliana embryos

We report the use of a derivative of the green fluorescent protein (GFP) to directly label the plant vacuole in live, unfixed tissues of stably transformed transgenic plants. We used the developmentally regulated soybean seed lectin promoter and the 32 amino acids of the soybean lectin amino terminal signal sequence to create an in-frame fusion polypeptide with GFP (pLGFP5). This construct was transferred into Arabidopsis thaliana by vacuum infiltration, and the transformed lines were characterized by DNA blotting and immunoblotting to detect the presence and expression of the GFP gene. GFP fluorescence was detected in the protein storage vacuoles of developing Arabidopsis embryos as imaged by fluorescence microscopy. Very little signal was detected in any other compartments including the cell wall. Thus, despite the absence of vacuolar sorting signals in GFP and other foreign proteins fused to the lectin sequence, the 32-amino-acid lectin signal sequence has general utility to direct foreign proteins to the protein storage vacuoles in seeds.