The sequence and expression of the gamma-VPE gene, one member of a family of three genes for vacuolar processing enzymes in Arabidopsis thaliana

Abstract

Vacuolar processing enzymes (VPEs) are responsible for the maturation of seed proteins. Southern blot analysis showed that a family of genes for VPEs in Arabidopsis thaliana was composed of three genes, for alpha-VPE, beta-VPE and gamma-VPE, respectively. The gene for gamma-VPE was isolated from a genomic library. It was composed of nine exons and eight introns. The positions of the introns were fully conserved among the three genes, with the exception that the alpha-VPE gene was missing the fifth intron found in the beta-VPE and gamma-VPE genes. The predicted gamma-VPE protein was 80% and 57% identical in terms of amino acid sequence to the alpha-VPE protein and beta-VPE protein, respectively. Northern blot analysis demonstrated that the gamma-VPE gene was expressed predominantly in the stems, with a lower level of expression in rosette and cauline leaves. However, the expression was not detected in roots, flowers plus buds, or green siliques, in contrast to the high-level expression of the beta-VPE gene in the flowers plus buds. Thus, gamma-VPE seems to be an isoform that is specific to vegetative organs. Members of the VPE family can be separated into two subfamilies, one that is specific to seeds and another that is specific to vegetative organs, such as leaves and stems. The members of the seed subfamily might function in the protein-storage vacuoles of seeds, while those of the vegetable subfamily might function in the lytic vacuoles of non-storage organs.