Molecular cloning and characterisation of a cDNA encoding a putative alkaline alpha-galactosidase from grapevine (Vitis vinifera L.) that is differentially expressed under osmotic stress

The expression of a gene originally identified by means of a salt-stress-associated partial cDNA showing a genotype-dependent response, was studied upon exposure to salt and drought stress and during seed development of grapevines. The complete open reading frame has been cloned and the corresponding untranslated regions have been characterized by 5′- and 3′-RACE leading to a refinement and correction of the predicted gene model in the recent 12× Vitis genome assembly. The open reading frame of the single copy gene designated Vv-α-gal/SIP encodes for a polypeptide of 774 amino acids with a calculated molecular mass of 84.9 kDa. Protein sequence comparisons suggest that the gene belongs to a growing family of plant-specific alkaline α-galactosidases. 5′-RACE identified a not yet documented transcript species derived from the same gene locus, which does not lead to the formation of a full-length transcript. The “aberrant” transcript harbours an alternative 5′-UTR and originates from an internal transcriptional start site 1.4 kb downstream of the predominant transcriptional start site. Levels of transcripts containing the different 5′-UTRs were compared under salt stress conditions.