Protein phosphorylation is one of the most important mechanisms to control cellular functions in response to external and endogenous signals. Mitogen-activated protein kinases (MAPK) are universal signaling molecules in eukaryotes that mediate the intracellular transmission of extracellular signals resulting in the induction of appropriate cellular responses. MAPK cascades are composed of four protein kinase modules: MAPKKK kinases (MAPKKKKs), MAPKK kinases (MAPKKKs), MAPK kinases (MAPKKs) and MAPKs. In plants, MAPKs are activated in response to abiotic stresses, wounding, and hormones, and during plant pathogen interactions and cell division. In this report, we performed a complete inventory of MAPK cascades genes in Vitis vinifera, the whole genome of which has been sequenced. By comparison with MAPK, MAPK kinases, MAPK kinase kinases and MAPK kinase kinase kinase kinase members of Arabidopsis thaliana, we revealed the existence of 14 MAPKs, 5 MAPKKs, 62 MAPKKKs, and 7 MAPKKKKs in Vitis vinifera. We identified orthologs of V. vinifera putative MAPKs in different species, and ESTs corresponding to members of MAPK cascades in various tissues. This work represents the first complete inventory of MAPK cascades in V. vinifera and could help elucidate the biological and physiological functions of these proteins in V. vinifera.

The ATP-binding cassette (ABC) protein superfamily constitutes one of the largest protein families known in plants. In this report, we performed a complete inventory of ABC protein genes in Vitis vinifera, the whole genome of which has been sequenced. By comparison with ABC protein members of Arabidopsis thaliana, we identified 135 putative ABC proteins with 1 or 2 NBDs in V. vinifera. Of these, 120 encode intrinsic membrane proteins, and 15 encode proteins missing TMDs. V. vinifera ABC proteins can be divided into 13 subfamilies with 79 “full-size,” 41 “half-size,” and 15 “soluble” putative ABC proteins. The main feature of the Vitis ABC superfamily is the presence of 2 large subfamilies, ABCG (pleiotropic drug resistance and white-brown complex homolog) and ABCC (multidrug resistance-associated protein). We identified orthologs of V. vinifera putative ABC transporters in different species. This work represents the first complete inventory of ABC transporters in V. vinifera. The identification of Vitis ABC transporters and their comparative analysis with the Arabidopsis counterparts revealed a strong conservation between the 2 species. This inventory could help elucidate the biological and physiological functions of these transporters in V. vinifera.

Hexokinase catalyses the first step in the metabolism of glucose, but has also been proposed to be involved in sugar sensing and signalling in both yeasts and plants. The substrates of hexokinase such as glucose (Glc) and fructose (Fruc) are also the most important sugars during grape berry ripening. The grapevine proteome database was analysed to investigate the roles of hexokinases in grape berry growth and development. Six hexokinase genes displaying high nucleotide sequence identity (72 – 87%) with hexokinase genes in other species were identified. Most of the Vitis vinifera hexokinase (VvHXK) genes had a highly conserved genomic structure consisting of nine exons and eight introns. A search for cis–regulatory elements in the promoter regions of all six hexokinase genes revealed that most were probably regulated by light, sugar, phytohormones, or abiotic stress. The isolation and expression of a hexokinase cDNA from V. vinifera ‘Sultanine’, named VvHXK3, was also reported. Analysis of the predicted amino acid sequence of VvHXK3 suggested that the protein could be a chloroplast-stromal hexokinase with a possible transit peptide cleavage site after amino acid residue 26. The VvHXK3 gene was differentially expressed in a variety of organs including berries, leaves, roots, and pollen, but its expression was highest in berries during their early development and at the start of ripening. To determine its function, VvHXK3 cDNA was expressed in a triple mutant yeast strain that lacked the ability to phosphorylate Glc and Fru and, therefore, was unable to grow on these sugars as sole carbon source. Mutant yeast cells that expressed VvHXK3 grew on both Glc and Fru, indicating that VvHXK3 could complement this mutant and had hexokinase activity.

Bax, a multidomain pro‐apoptotic Bcl‐2 protein, localizes to the endoplasmic reticulum (ER), where it regulates ER stress‐induced apoptosis. Adaptation to ER stress depends on the activation of an integrated signal transduction pathway known as the unfolded protein response (UPR). This study examined the death‐inducing activity of Bax and its ability to induce UPR signalling pathways in yeast. We observed that inhibition of global translation in yeast cells expressing Bax correlated with Bax‐induced cell death. Using a lacZ reporter containing several UPR cis‐activating regulatory elements, we also found that Bax directly activated the UPR. Furthermore, this correlated with the splicing of HAC1 mRNA, a gene involved in UPR activation. Bax induced expression of representative UPR target genes such as KAR2, DER1 and GCN4. Finally, we found that Ire1p function is critical for Bax‐induced cell death. Copyright © 2012 John Wiley & Sons, Ltd.