Dan Cosgrove, Penn State, Rethinking the architecture of growing cell walls and the mechanisms of cell wall loosening

Abstract:  For two decades the major model of primary cell walls hypothesizes that xyloglucan binds to cellulose microfibril surfaces, coating them and tethering adjacent microfibrils into a strong yet extensible network. This 'tethered network' hypothesis places xyloglucan at the center of the control of cell wall mechanics and wall extensibility. It is supported by binding data and by microscopy, yet NMR studies appear to be at odds with this concept and as does the nearly normal growth phenotype of an Arabidopsis line lacking xyloglucan. We have investigated cell wall architecture by probing cell walls with a combination of substrate-specific endoglucanases and biomechanical assays (creep, stress/strain analyses). These results, along with analyses of xyloglucan-deficient cell walls, high resolution imaging and nanomechanical mapping by atomic force microscopy of cell wall surfaces, have led us back to the blackboard to consider alternative architectures for primary cell walls.