The plant extracellular matrix: in a new expansive mood.

Plant cell expansion requires the integration of local wall loosening and the controlled deposition of new wall materials. Although we still know little of the latter process, two new classes of proteins have been discovered that may function in the former. Evidence is increasing that the plant extracellular matrix can exert a regulatory effect over cell behaviour. New approaches, in particular a molecular genetic analysis of cell wall mutants, are likely to speed up our understanding of wall biosynthesis, structure and function.