Identification and Expression Analysis of Wheat Vacuolar Processing Enzymes (VPEs)

Vacuolar proteins are associated with various functions, such as germination and programmed cell death (PCD) activity. Precursors of most vacuolar proteins are synthesized in the rough endoplasmic reticulum (rough ER). They are transported to the vacuoles, and converted into the mature forms. Vacuolar processing enzyme (VPE) is responsible for maturation of vacuolar proteins. Intensive studies revealed that VPE-mediated system is important for vacuolar functions in plant. However, the role and mechanism of VPE still remain to be elucidated, especially in wheat. Here, we isolated three putative wheat VPE genes which were designated as TaVPE2, 3 and 4. To investigate the expression of TaVPEs, RT-PCR was conducted using RNAs extracted from caryopsis, pericarp, leaf and/or stem tissues at seed development stage and leaf, stem and/or root of seedling with phytohormone or abiotic stress treatment. Transcript accumulation of TaVPEs including TaVPE1 was displayed in caryopsis during seed development stage. TaVPE1, TaVPE2 and TaVPE3 were expressed in root under abiotic stress whereas they showed no or very weak expression pattern in other tissue. Promoter region of TaVPEs contain many environmental-associated and tissue-specific cis-elements. In fact, VPEs sensitively responded to certain treatment condition. TaVPEs belong to seed type VPE in phylogenetic grouping. However, expression pattern of TaVPEs is different from other seed type VPEs. The classification into vegetative and seed type VPE according to gene expression patterns cannot be applied to TaVPEs.