First published online December 28, 2007; 10.1105/tpc.107.050609
The Plant Cell 19:4007-4021 (2007)
© 2007 American Society of Plant Biologists
The Arabidopsis MUM2 Gene Encodes a β-Galactosidase Required for the Production of Seed Coat Mucilage with Correct Hydration Properties[W]
Gillian H. Deana,
Huanquan Zhenga,1,
Jagdish Tewarib,2,
Jun Huanga,
Diana S. Younga,
Yeen Ting Hwanga,
Tamara L. Westerna,1,
Nicholas C. Carpitac,
Maureen C. McCannb,
Shawn D. Mansfieldd and
George W. Haughna,3
a Department of Botany, University of British Columbia, Vancouver, Canada V6T 1Z4
b Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
c Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907
d Department of Wood Science, University of British Columbia, Vancouver, Canada V6T 1Z4
3 Address correspondence to haughn{at}interchange.ubc.ca.
Seed coat development in Arabidopsis thaliana involves a complex pathway where cells of the outer integument differentiate into a highly specialized cell type after fertilization. One aspect of this developmental process involves the secretion of a large amount of pectinaceous mucilage into the apoplast. When the mature seed coat is exposed to water, this mucilage expands to break the primary cell wall and encapsulate the seed. The mucilage-modified2 (mum2) mutant is characterized by a failure to extrude mucilage on hydration, although mucilage is produced as normal during development. The defect in mum2 appears to reside in the mucilage itself, as mucilage fails to expand even when the barrier of the primary cell wall is removed. We have cloned the MUM2 gene and expressed recombinant MUM2 protein, which has β-galactosidase activity. Biochemical analysis of the mum2 mucilage reveals alterations in pectins that are consistent with a defect in β-galactosidase activity, and we have demonstrated that MUM2 is localized to the cell wall. We propose that MUM2 is involved in modifying mucilage to allow it to expand upon hydration, establishing a link between the galactosyl side-chain structure of pectin and its physical properties.
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