Mixed-linkage β-glucan : xyloglucan endotransglucosylase, a novel wall-remodelling enzyme from Equisetum (horsetails) and charophytic algae
Article first published online: 4 APR 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
The Plant Journal
Volume 55, Issue 2, pages 240–252, July 2008
How to Cite
Fry, S. C., Mohler, K. E., Nesselrode, B. H.W.A. and Franková, L. (2008), Mixed-linkage β-glucan : xyloglucan endotransglucosylase, a novel wall-remodelling enzyme from Equisetum (horsetails) and charophytic algae. The Plant Journal, 55: 240–252. doi: 10.1111/j.1365-313X.2008.03504.x
- Issue published online: 8 JUL 2008
- Article first published online: 4 APR 2008
- Received 2 January 2008; revised 25 February 2008; accepted 11 March 2008.
Vol. 55, Issue 6, 1062, Article first published online: 5 SEP 2008
- mixed-linkage β-glucan;
- cell wall
Mixed-linkage (13,14)-β-d-glucan (MLG), a hemicellulose long thought to be confined to certain Poales, was recently also found in Equisetum; xyloglucan occurs in all land plants. We now report that Equisetum possesses MLG:xyloglucan endotransglucosylase (MXE), which is a unique enzyme that grafts MLG to xyloglucan oligosaccharides (e.g. the heptasaccharide XXXGol). MXE occurs in all Equisetum species tested (Equisetum arvense, Equisetum fluviatile, Equisetum hyemale, Equisetum scirpoides, Equisetum telmateia and Equisetum variegatum), sometimes exceeding xyloglucan endotransglucosylase (XET) activity. Charophytic algae, especially Coleochaete, also possess MXE, which may therefore have been a primordial feature of plant cell walls. However, MXE was negligible in XET-rich extracts from grasses, dicotyledons, ferns, Selaginella and bryophytes. This and the following four additional observations indicate that MXE activity is not the result of a conventional xyloglucan endotransglucosylase/hydrolase (XTH): (i) XET, but not MXE, activity correlates with the reaction rate on water-soluble cellulose acetate, hydroxyethylcellulose and carboxymethylcellulose, (ii) MXE and XET activities peak in old and young Equisetum stems, respectively, (iii) MXE has a higher affinity for XXXGol (Km ∼ 4 μM) than any known XTH, (iv) MXE and XET activities differ in their oligosaccharide acceptor-substrate preferences. High-molecular-weight (Mr) xyloglucan strongly competes with [3H]XXXGol as the acceptor-substrate of MXE, whereas MLG oligosaccharides are poor acceptor-substrates. Thus, MLG-to-xyloglucan grafting appears to be the favoured activity of MXE. In conclusion, Equisetum has evolved MLG plus MXE, potentially a unique cell wall remodelling mechanism. The prominence of MXE in mature stems suggests a strengthening/repairing role. We propose that cereals, which possess MLG but lack MXE, might be engineered to express this Equisetum enzyme, thereby enhancing the crop mechanical properties.