Journal Article

Functional Identification of Arabidopsis <i>ATSIP2</i> (At3g57520) as an Alkaline α-Galactosidase with a Substrate Specificity for Raffinose and an Apparent Sink-Specific Expression Pattern

Shaun Peters, Aurélie Egert, Bruno Stieger and Felix Keller

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 10, pages 1815-1819
Published in print October 2010 | ISSN: 0032-0781
Published online August 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq127
Functional Identification of Arabidopsis ATSIP2 (At3g57520) as an Alkaline α-Galactosidase with a Substrate Specificity for Raffinose and an Apparent Sink-Specific Expression Pattern

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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.

Keywords: Alkaline α-galactosidase; Phloem unloading; Raffinose; Sf9 insect cells; Sink metabolism

Journal Article.  2522 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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