AtVAM3, a homolog of Q_a-SNARE VAM3, is involved in development of myrosin cells in Arabidopsis

Abstract

Yeast VAM3 is a Q_a-SNARE that is involved in vacuolar transport of proteins and vacuolar assembly. Previously, we showed that atvam3 mutants accumulate large amounts of thioglucoside glucohydrolase (TGG), which hydrolyze glucosinolates to produce toxic compounds for repelling pests. Myrosin cells in Capparales plants are idioblasts that accumulate TGG. An immunogold revealed TGGs were specifically localized in the vacuole of myrosin cells in atvam3 mutants. This result indicates that TGGs are normally transported to vacuoles in these mutants and that AtVAM3 is not essential for vacuolar transport of TGG. Myrosin cells were scattered along leaf veins in wild-type leaves, while they were abnormally distributed in atvam3 leaves. The mutants developed a network of myrosin cells throughout the leaves: myrosin cells were not only distributed continuously along leaf veins, but were also observed independent of leaf veins. Our results suggest that AtVAM3 has a plant-specific function in development of myrosin cells.