βVPE is involved in tapetal degradation and pollen development by activating proprotease maturation in Arabidopsis thaliana

Vacuolar processing enzyme (VPE) is responsible for the maturation and activation of vacuolar proteins in plants. We found that betaVPE was involved in tapetal degradation and pollen development by transforming proproteases into mature protease in Arabidopsis thaliana. betaVPE was expressed specifically in the tapetum from stages 5 to 8 of anther development. The betaVPE protein first appeared as a proenzyme and was transformed into the mature enzyme before stages 7-8. The recombinant betaVPE protein self-cleaved and transformed into a 27 kDa mature protein at pH 5.2. The mature betaVPE protein could induce the maturation of CEP1 in vitro. betavpe mutants exhibited delayed vacuolar degradation and decreased pollen fertility. The maturation of CEP1, RD19A, and RD19C was seriously inhibited in betavpe mutants. Our results indicate that betaVPE is a crucial processing enzyme that directly participates in the maturation of cysteine proteases before vacuolar degradation, and is indirectly involved in pollen development and tapetal cell degradation.