Functional identification of Arabidopsis ATSIP2 (At3g57520) as an alkaline α-galactosidase with a substrate specificity for raffinose and an apparent sink-specific expression pattern.
Arabidopsis ATSIP2 has recently been suggested to be a raffinose synthase gene. However, it has high amino acid identity to functionally characterized alkaline α-galactosidases from Cucumis melo and Zea mays. Using the Sf9 insect cell expression system, we demonstrate that recombinant ATSIP2 is a genuine alkaline α-galactosidase with a distinct substrate specificity for raffinose, and not a raffinose synthase. A β-glucuronidase reporter construct using the ATSIP2 promoter shows that ATSIP2 is strongly expressed in sink tissues of Arabidopsis, i.e. sink leaves and non-xylem parts of the root stele, suggesting a physiological function in raffinose phloem unloading.
Peters
Shaun
S
Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, 8008 Zürich, Switzerland.
Egert
Aurélie
A
Stieger
Bruno
B
Keller
Felix
F
D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D018506:Gene Expression Regulation, Plant; D007313:Insecta / Q000166:cytology; D052585:Phloem / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D018749:RNA, Plant / Q000235:genetics; D011887:Raffinose / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D000519:alpha-Galactosidase / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D018749:RNA, Plant; D011994:Recombinant Proteins; D000519:alpha-Galactosidase; D011887:Raffinose