Elucidation of the biochemical and physiological function of the vacoular annexin, VCaB42
Abstract
A calcium-dependent membrane-binding protein of the annexin family, VCaB42, has previously been shown to associate with vacuolar vesicles at physiological levels of calcium. This study has focused on dissecting VCaB42 protein accumulation in several plant systems in the continued effort at elucidating its function in plant cells. First, the association of VCaB42 with vacuoles has been confirmed in tobacco by its enrichment in isolated intact vacuoles and its depletion when protoplasts are evacuolated, a result that compares favorably with the vacuolar ATPase, but not with calnexin, a marker for the endoplasmic reticulum. As there are two types of vacuoles (lytic vacuoles and PSVs), VCaB42 was also studied during embryogenesis, a developmental system with remarkable vacuole dynamics. VCaB42 protein accumulated early in embryogenesis at a time when lytic-type vacuoles predominate and not with the development of PSVs that occurs later. This correlation was also extended by drought-treatment of cotton which alters the development fate of these two vacuole types. Because VCaB42 is an annexin linked to the developmental of lytic-type vacuoles and given the putative function of annexins in vesicle fusion, a role for this protein in the vacuolation process of expanding cells has been hypothesized. The observation that VCaB42 levels correlate with both age-associated and hormonally-induced changes in cell volume in tobacco suspension cultured cells is consistent with this hypothesis. A similar role in vacuolation has been suggested for the small Rho-type G protein, called Rop, to which VCaB42 shows partial, and short-lived co-localization. To address a causal role for VCaB42 in vacuole formation, the corresponding cDNA has now been isolated from tobacco. It encodes an annexin, but it is distinguished from previously identified tobacco cDNAs, supporting the notion that VCaB42 is a unique representative of the annexin family. Current studies are focused on understanding the relationship of VCaB42 with other related annexins and on the direct alteration (sense/overexpression, antisense/underexpression) of VCaB42 protein levels in transgenic tobacco cells using a tetracycline-inducible promoter.
Degree
Ph.D.
Advisors
Randall, Purdue University.
Subject Area
Plant pathology|Molecular biology|Biochemistry|Agronomy
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