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...

Abscisic acid (ABA) induces the expression of a battery of genes in mediating plant responses to environmental stresses. Here we report one of the early ABA-inducible genes in barley (Hordeum vulgare L.), HVA22, which shares little homology with other ABA-responsive genes such as LEA (late embryogenesis-abundant) and RAB (responsive to ABA) genes. In grains, the expression of HVA22 gene appears to be correlated with the dormancy status. The level of HVA22 mRNA increases during grain development, and declines to an undetectable level within 12 h after imbibition of non-dormant grains. In contrast, the HVA22 mRNA level remains high in dormant grains even after five days of imbibition. Treatment of dormant grains with gibberellin (GA) effectively breaks dormancy with a concomitant decline of the level of HVA22 mRNA. The expression of HVA22 appears to be tissue-specific with the level of its mRNA readily detectable in aleurone layers and embryos, yet undetectable in the starchy endosperm. The expression of HVA22 in vegetative tissues can be induced by ABA and environmental stresses, such as cold and drought. Apparent homologues of this barley gene are found in phylogenetically divergent eukaryotic organisms, including cereals, Arabidopsis, Caenorhabditis elegans, man, mouse and yeast, but not in any prokaryotes. Interestingly, similar to barley HVA22, the yeast homologue is also stress-inducible. These observations suggest that the HVA22 and its homologues encode a highly conserved stress-inducible protein which may play an important role in protecting cells from damage under stress conditions in many eukaryotic organisms.

In eukaryotic cells, faithful chromosome segregation depends upon the physical pairing, or cohesion, between sister chromatids. Budding yeast CTF7/ECO1 (herein termed CTF7) encodes an essential protein required to establish cohesion during S-phase and associates with DNA replication factors [1-10]. However, the molecular mechanism by which Ctf7p establishes cohesion remains unknown. In vitro characterization of Ctf7p as an acetyltransferase led to the model that this activity provides for Ctf7p's essential function [11]. However, in vivo Ctf7p substrates have yet to be documented, nor has an in vivo acetyltransferase activity been demonstrated even when Ctf7p is overexpressed [11] (A. Brands and R.V. Skibbens, unpublished data). In fact, the effects of acetylationdefective Ctf7p (ctf7 ack-) in yeast remain to be rigorously tested, leaving unanswered the critical questions of whether Ctf7p acetyltransferase activity is essential for cell viability and to what extent this activity is required for the establishment of cohesion. Here, we show that yeast strains harboring acetyltransferasedefective alleles [11] as the sole source of Ctf7p function exhibit robust growth and high fidelity chromosome transmission. We first used a plasmid loss assay to test whether ctf7 ackalleles could support cell viability. CEN TRP1 plasmids containing wild-type CTF7 or ctf7 ackalleles exhibiting abrogated or greatly diminished acetyltransferase activity in vitro [11] were transformed into an ade2;ade3

High-fidelity chromosome segregation requires that the sister chromatids produced during S phase also become paired during S phase. Ctf7p (Eco1p) is required to establish sister chromatid pairing specifically during DNA replication. However, Ctf7p also becomes active during G 2 /M in response to DNA damage. Ctf7p is a phosphoprotein and an in vitro target of Cdc28p cyclin-dependent kinase (CDK), suggesting one possible mechanism for regulating the essential function of Ctf7p. Here, we report a novel synthetic lethal interaction between ctf7 and cdc28. However, neither elevated CDC28 levels nor CDC28 Cak1p-bypass alleles rescue ctf7 cell phenotypes. Moreover, cells expressing Ctf7p mutated at all full-and partial-consensus CDKphosphorylation sites exhibit robust cell growth. These and other results reveal that Ctf7p regulation is more complicated than previously envisioned and suggest that CDK acts in sister chromatid cohesion parallel to Ctf7p reactions.