Functional Studies of a Stress Protein Family: Subcellular Localizations of AtHVA22a-e Proteins in Arabidopsis
Date Issued
2008
Date
2008
Author(s)
Lu, Yung-Yu
Abstract
HVA22 is an ABA- and stress-inducible protein that was first isolated from barley aleurone cells. Homologues of HVA22 have been found only in eukaryotes. The yeast homolog, Yop1 is proposed to be involved in vesicle trafficking, and has been shown to stabilize tubule formation to comprise ER network in vivo. As a result, these DP1/TB2/HVA22 family proteins are proposed to be involved in vesicle trafficking pathways in plant cells. There are 11 HVA22 homologues in Arabidopsis, designed as AtHVA22a-k. Among these homologues, AtHVA22a-e contain three potential transmembrane domains, and are phylogenetically closer to yeast Yop1 and barley HVA22. However, AtHVA22f, g, k are pseudogenes and AtHVA22 h-j do not contain significant potential transmembrane domains. o investigate the functions of AtHVA22a-e proteins in vivo, we generated AtHVA22a-e:GFP fusion proteins and transiently expressed them in Arabidopsis mesophyll protoplasts. By confocal microscopy, we investigated the subcellular localizations of AtHVA22a-e proteins. Our observations indicated that each of AtHVA22a, b, c, d and e had specific cellular localizations. AtHVA22b and e were localized to Golgi apparatus. AtHVA22d was localized to both endoplasmic reticulum (ER) and Golgi apparatus. The subcellular localizations of AtHVA22a and c remained unclear; however, they seemed to interact with AtHVA22b. These results indicated that each of AtHVA22a-e proteins had a specific role in vesicular trafficking. Combined with previous studies of tissue-specific and differential expression levels of AtHVA22 genes in response to ABA and abiotic stresses, we propose that AtHVA22a-e may function in stress-induced vesicular trafficking to establish stress tolerance in plants. In particular, AtHVA22b, d and e may be involved in the ER-Golgi trafficking pathways. On the other hand, AtHVA22a and c are likely not involved in the same pathway under normal condition.
Subjects
subcellular localization
GFP
stress-inducible proteins
endomembrane system
vesicle trafficking
ER (endoplasmic reticulum)
Golgi apparatus
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