Abstract
Vacuolar processing enzymes (VPEs) are responsible for the maturation of vacuolar proteins. Previous our studies of three Arabidopsis VPEs have shown their differential expression and physiological functions. Here we report that a fourth Arabidopsis VPE, δVPE, which was recently found in the database, is involved in seed coat formation. δVPE was specifically and transiently expressed in the two cell layers of the testa (ii2 and ii3) at an early stage of seed development. Electron microscopy reveled that at this stage, cell death accompanying cell shrinkage occurs in the layers. In a δVPE-deficient mutant, cell death of the two layers of the testa was delayed. Immunocytochemical analysis localized δVPE to electron-dense structures inside and outside cell walls in the layers in association of cell death. Our results suggest that δVPE is involved in programmed cell death of limited cell layers, the purpose of which is to a form seed coat.
