A novel α-amylase gene is transiently upregulated during low temperature exposure in apple fruit

Abstract

An α-amylase gene product was isolated from apple fruit by reverse- transcriptase PCR using redundant primers, followed by 5' and 3' RACE. The gene is a member of a small gene family. It encodes a putative 46.9 kDa protein that is most similar to an α-amylase gene from potato (GenBank accession M79328). In apple fruit this new gene was expressed at low levels, as detected by reverse-transcriptase PCR, in a number of plant tissues and during fruit development. Highest levels of mRNA for this transcript were observed 3 to 9 days after placing apple fruit at 0.5 °C. Phylogenetic analysis of amino acid sequence places the potato and apple proteins as a distinct and separate new subgroup within the plant α-amylases, which appears to have diverged prior to the split between monocotyledonous and dicotyledonous plants. These two divergent α-amylases lack the standard signal peptide structures found in all other plant α-amylases, and have sequence differences within the B-domain and C-domain. However, comparisons with structures of known starch hydrolases suggest that these differences are unlikely to affect the enzymatic α-1,4-amylase function of the protein. This is the first report of upregulation of a dicotyledonous α-amylase in response to low temperature, and confirms the presence of a new family of α- amylases in plants.