Function of a Plant Stress-Induced Gene, HVA22. Synthetic Enhancement Screen with Its Yeast Homolog Reveals Its Role in Vesicular Traffic

Abstract

Expression of the barley (Hordeum vulgare) HVA22 gene is induced by environmental stresses, such as dehydration, salinity, and extreme temperatures, and by a plant stress hormone, abscisic acid. Genes sharing high level of sequence similarities with HVA22 exist in diverse eukaryotic organisms, including animals, plants, and fungi, but not in any prokaryotic organisms. The yeast (Saccharomyces cerevisiae) HVA22 homolog, Yop1p, has been shown to interact with the GTPaseinteracting protein, Yip1p. Deletion of YOP1 led to only a modest reduction of the stationary phase titer at 37C. A synthetic enhancement mutant screen was performed in the yop1 deletion background to identify genes interacting with YOP1. The open reading frame YOR165W (renamed SEY1 for synthetic enhancement of YOP1) was identified as a YOP1-dependent complementation gene. The yeast SEY1 is a homolog of the Arabidopsis RHD3 gene whose mutations cause the accumulation of transport vesicles near the tips of defective root hairs. The yeast double mutant of yop1 and sey1 is defective in vesicular traffic as evidenced by the accumulation of transport vesicles and the decrease in invertase secretion. Based on these observations, we suggest that Yop1p/HVA22 regulates vesicular traffic in stressed cells either to facilitate membrane turnover, or to decrease unnecessary secretion.Sessile organisms such as plants and fungi have developed sophisticated responses to environmental stresses that allow them to tolerate adverse conditions (Hohmann and Willem, 1997;Hoekstra et al., 2001). One approach to understanding these responses is through the identification of genes that are up-regulated during abiotic stress, followed by functional analyses of the corresponding gene products. In plants, stress stimulates the production of the phytohormone abscisic acid (ABA) (Zeevaart and Creelmann, 1988; Bray, 2002), which induces the expression of a variety of genes (Chandler and Robertson, 1994; Bray, 2002). Furthermore, elevated levels of ABA are correlated with late embryogenesis and the onset and maintenance of seed dormancy (Zeevaart and Creelmann, 1988). Because the dehydration of the seed during late embryogenesis is a normal part of the developmental program, these tissues provide a valuable resource for the identification of genes that are involved in desiccation tolerance.In cereals, a metabolically active tissue, the aleurone layer, surrounds the starchy endosperm of the seed. Upon germination, the embryo produces the phytohormone GA, which induces the production of hydrolytic enzymes by the aleurone tissue. These enzymes are secreted into the endosperm, where they liberate sugars and amino acids for the growing embryo. ABA blocks the production of these enzymes at the transcriptional level (Lovegrove and Hooley, 2000). The gene HVA22 was originally identified as a transcript that accumulates in barley (Hordeum vulgare) aleurone tissue upon treatment with ABA, and was later found to be induced in vegetative tissues exposed to ABA, drought, or cold stress (Shen et...

Expression Analysis of Genes Associated with the Induction of the Carbon-Concentrating Mechanism in Chlamydomonas reinhardtii

“…It has been reported that the expression of barley (Hordeum vulgare) HVA22 is induced by several environmental stresses, such as dehydration, salinity, and extreme temperatures, as well as by a plant stress hormone, abscisic acid (Brands and Ho, 2002).…”

The Transcription Factors HvABI5 and HvVP1 Are Required for the Abscisic Acid Induction of Gene Expression in Barley Aleurone Cells

“…Although both genes encode proteins with unknown functions, it has been shown that constitutive expression of HVA1 , which encodes a group 3 LEA protein, can confer drought resistance to transgenic plants (Xu et al, 1996). On the other hand, HVA22 probably is involved in intracellular vesicular trafficking (Brands and Ho, 2002). Promoter analyses of these two genes have demonstrated that two cis elements, an ACGT-box and a coupling element (together constituting ABA response complexes: ABRC3 in HVA1 and ABRC1 in HVA22 ), are necessary and sufficient for their induction by ABA (Shen and Ho, 1997).…”

Cloning of the Full-length cDNA of the Wheat Involved in Salt Stress: Root Hair Defective 3 Gene (RHD3)

“…The yeast homologue of RHD3, Sey1p, is a synthetic enhancer of Yop1p, whereas Yop1p and its conjunction protein Yip1p are integral membrane proteins that play a role in membrane traffic and endoplasmic reticulum-Golgi vesicle fusion. The protein Yip1p interacts with the Rab GTPases Ypt1p and Ypt31p/32p to regulate vesicle traffic in yeast (Yang et al 1998;Calero et al 2001;Brands and Ho 2002;Ortiz et al 2002;Barrowman et al 2003). Therefore, this implies that a role for RHD3 in facilitating Rab GTPase function in the Golgi in Arabidopsis could account for the diverse phenotypes in cell growth, endoplasmic reticulum-Golgi traffic, and vacuole organization (Zheng et al 2004).…”