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Free Content Vacuolar processing enzyme is up-regulated in the lytic vacuoles of vegetative tissues during senescence and under various stressed conditions

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Summary

Vacuolar processing enzyme (VPE) has been shown to be responsible for maturation of various seed proteins in protein-storage vacuoles. Arabidopsis has three VPE homologues; VPE is specific to seeds and αVPE and VPE are specific to vegetative organs. To investigate the activity of the vegetative VPE, we expressed the VPE in a pep4 strain of the yeast Saccharomyces cerevisiae and found that VPE has the ability to cleave the peptide bond at the carbonyl side of asparagine residues. An immunocytochemical analysis revealed the specific localization of the VPE in the lytic vacuoles of Arabidopsis leaves that had been treated with wounding. These findings indicate that VPE functions in the lytic vacuoles as the VPE does in the protein-storage vacuoles. The VPE promoter was found to direct the expression of the -glucuronidase reporter gene in seeds and the root tip of transgenic Arabidopsis plants. On the other hand, both the αVPE and VPE promoters directed the expression in senescent tissues, but not in young intact tissues. The mRNA levels of both αVPE and VPE were increased in the primary leaves during senescence in parallel with the increase of the mRNA level of a senescence-associated gene (SAG2). Treatment with wounding, ethylene and salicylic acid up-regulated the expression of αVPE and VPE, while jasmonate slightly up-regulated the expression of VPE. These gene expression patterns of the VPEs were associated with the accumulation of vacuolar proteins that are known to respond to these treatments. Taken together, the results suggest that vegetative VPE might regulate the activation of some functional proteins in the lytic vacuoles.
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Document Type: Original Article

Affiliations: Department of Cell Biology, National Institute for Basic Biology, Okazaki 444, Japan, and

Publication date: July 1, 1999

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