AOBPreview originally published online on May 19, 2009
Annals of Botany 2009 104(2):197-204; doi:10.1093/aob/mcp120
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BOTANICAL BRIEFING |
Re-interpreting the role of endo-β-mannanases as mannan endotransglycosylase/hydrolases in the plant cell wall
1 The New Zealand Institute for Plant and Food Research Limited, Mt. Albert Research Centre, Private Bag 92 169, Auckland, New Zealand
2 Nestlé Research Centre, Nestec Ltd, Vers-chez-les-blanc, PO Box 44, CH-1000, Lausanne 26, Switzerland
* For correspondence. E-mail rschroeder{at}hortresearch.co.nz
Received: 7 October 2008 Returned for revision: 15 December 2008 Accepted: 16 April 2009 Published electronically: 19 May 2009
Background: Mannans are hemicellulosic polysaccharides in the plant primary cell wall with two major physiological roles: as storage polysaccharides that provide energy for the growing seedling; and as structural components of the hemicellulose–cellulose network with a similar function to xyloglucans. Endo-β-mannanases are hydrolytic enzymes that cleave the mannan backbone. They are active during seed germination and during processes of growth or senescence. The recent discovery that endo-β-mannanase LeMAN4a from ripe tomato fruit also has mannan transglycosylase activity requires the role of endo-β-mannanases to be reinterpreted.
Aims: In this review, the role of endo-β-mannanases as mannan endotransglycosylase/hydrolases (MTHs) in remodelling the plant cell wall is considered by analogy to the role of xyloglucan endotransglucosylase/hydrolases (XTHs). The current understanding of the reaction mechanism of these enzymes, their three-dimensional protein structure, their substrates and their genes are reported.
Future outlook: There are likely to be more endohydrolases within the plant cell wall that can carry out hydrolysis and transglycosylation reactions. The challenge will be to demonstrate that the transglycosylation activities shown in vitro also exist in vivo and to validate a role for transglycosylation reactions during the growth and development of the plant cell wall.
Key words: Cell wall, endo-β-mannanase, endohydrolase, mannan, endotransglycosylase
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