A PLASMA MEMBRANE-BOUND PUTATIVE ENDO-1,4-BETA-D-GLUCANASE IS REQUIRED FOR NORMAL WALL ASSEMBLY AND CELL ELONGATION IN ARABIDOPSIS

Endo-1,4-beta-D-glucanases (EGases) form a large family of hydrolytic enzymes in prokaryotes and eukaryotes, In higher plants, potential sub strates in vivo are xyloglucan and non-crystalline cellulose in the ce ll wall. Gene expression patterns suggest a role far EGases in various developmental processes such as leaf abscission, fruit ripening and c ell expansion. Using Arabidopsis thaliana genetics, we demonstrate the requirement of a specialized member of the EGase family for the corre ct assembly of the walls of elongating cells, KORRIGAN (KOR) is identi fied by an extreme dwarf mutant with pronounced architectural alterati ons in the primary cell wall. The KOR gene was isolated and encodes a membrane-anchored member of the EGase family, which is highly conserve d between mono- and dicotyledonous plants. KOR is located primarily in the plasma membrane and presumably acts at the plasma membrane-cell w all interface. KOR mRNA was found in all organs examined, and in the d eveloping dark-grown hypocotyl, mRNA levels were correlated with rapid cell elongation. Among plant growth factors involved in the control o f hypocotyl elongation (auxin, gibberellins and ethylene) none signifi cantly influenced KOR-mRNA levels. However, reduced KOR-mRNA levels we re observed in det2, a mutant deficient for brassinosteroids. Although the in vivo substrate remains to be determined, the mutant phenotype is consistent with a central role for KOR in the assembly of the cellu lose-hemicellulose network in the expanding cell wall.