We used family-12 endoglucanases with varying substrate specificities to probe the structure of the growing cell wall. The most popular model proposes that cellulose microfibrils are directly tethered to one another by xyloglucans (XyGs) that stick to cellulose surfaces or become entrapped during microfibril formation. Supporting this idea, we found that digestion by Cel12A, a glycosyl hydrolase family 12 endoglucanase, caused wall creep. In contrast, XEG, a XyG-specific endoglucanase, did not induce cell wall creep. From assays of wall mechanics in concert with analysis of xyloglucan oligosaccharides released by XEG and Cel12A, we see evidence for a protected form of XyG that controls cell wall mechanics. We also tested a suite of other endoglucanases with varying substrate specificities, leading to the same conclusion.  We conclude that XEG-susceptible XyG does not tether cellulose fibrils into a load-bearing network, but cellulose is somehow linked by a protected form of XyG.

Does xyloglucan really tether cellulose together in growing walls?  A study with family-12 endoglucanases

243rd National Meeting (2012)

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