Submitted to: Carbohydrate International Symposium
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2006
Publication Date: 7/24/2006
Citation: Tanaka, Y., Duke, S., Henson, C.A. 2006. Alpha-glucosidases from the glycoside hydrolase family 31 in germinating seeds and seedling leaves of barley. XXIIIrd International Carbohydrate Symposium, July 23-28, 2006, Whistler, Canada. 2006 CDROM. Interpretive Summary:
Technical Abstract: Of the four starch degrading enzymes in plants, only alpha-amylase and alpha-glucosidase have been extensively studied. Both alpha-amylase and alpha-glucosidase are important in germinating seeds in direct initiation of attack on starch grains. Five different alpha-glucosidases have been found in Arabidopsis and two in potato. These proteins all have the active site “W (I/N) DMNE” which is characteristic of alpha-glucosidases in the glycoside hydrolase family 31. However, the relative roles of the different forms of the enzyme are unclear. We have found and isolated four different alpha-glucosidase like proteins, Agl1, Agl2, Agl3, and Agl4 from barley (Hordeum vulgare L.). Based on sequence analysis we have determined that all four of these alpha-glucosidases are in the glycoside hydrolase family 31. Phylogenetic analysis showed that the Agl2 gene had a high degree of homology with that of several other plant species alpha-glucosidase genes. Western blot analysis using antibodies that discriminate between Agl1 and Agl2 proteins showed that both Agl1 and Agl2 were subject to post-translational degradation in seedling leaves and that Agl2 is not detected in germinating seeds. Quantitative polymerase chain reaction studies with geometric averaging of multiple internal control genes  revealed that the Agl2 gene was expressed at the same level in germinating seeds and leaves, whereas transcripts of Agl1 in germinating seeds are significantly higher than in seedling leaves. Differences in these transcripts and in the promoters of these two alpha-glucosidase genes will be presented in detail.