Subunit of the peripheral V1 complex of vacuolar ATPase essential for assembly or catalytic function. V-ATPase is responsible for acidifying a variety of intracellular compartments in eukaryotic cells. Required for Golgi organization and vacuole function in embryogenesis. V-ATPase is a heteromultimeric enzyme composed of a peripheral catalytic V1 complex (components A to H) attached to an integral membrane V0 proton pore complex (components: a, c, c'', d and e). Expressed mainly in the endosperm and surrounding maternal tissues during seed development. Mutant embryos are lethal, displaying variably enlarged cells with multiple nuclei, large vacuoles containing inclusions, abnormal organization of Golgi stacks, and cell wall defects. Belongs to the V-ATPase E subunit family.