Cell wall alterations in the Arabidopsis emb30 mutant

The Arabidopsis EMB30 gene is essential for controlling the polarity of cel l growth and for normal cell adhesion during seedling development. In this article, we show that emb30 mutations also affect the growth of undifferent iated plant cells and adult tissues. EMB30 possesses a Sec7 domain and, bas ed on similarities to other proteins, presumably functions in the secretory pathway. The plant cell wall depends on the secretory pathway to deliver i ts complex polysaccharides. We show that emb30 mutants have a cell wall def ect that sometimes allows material to be deposited into the interstitial sp ace between cells instead of being restricted to cell corners. In addition, pectin, a complex polysaccharide important for cell adhesion, appears to b e abnormally localized in emb30 plants. In contrast, localization of epitop es associated with xyloglucan or arabinogalactan was similar in wild-type a nd emb30 tissues, and the localization of a marker molecule to vacuoles app eared normal. Therefore, emb30 mutations do not cause a general defect in t he secretory pathway. Together, these results suggest that emb30 mutations result in an abnormal cell wall, which in turn may account for the defects in cell adhesion and polar cell growth control observed in the mutants.