PROCUSTE1 encodes a cellulose synthase required for normal cell elongationspecifically in roots and dark-grown hypocotyls of arabidopsis

Mutants at the PROCUSTE1 (PRC1) locus show decreased cell elongation, speci fically in roots and dark-grown hypocotyls. Cell elongation defects are cor related with a cellulose deficiency and the presence of gapped walls. Map-b ased cloning of PRC1 reveals that it encodes a member (CesA6) of the cellul ose synthase catalytic subunit family, of which at least nine other members exist in Arabidopsis. Mutations in another family member, RSW1 (CesA1), ca use similar cell wall defects in all cell types, including those in hypocot yls and roots, suggesting that cellulose synthesis in these organs requires the coordinated expression of at least two distinct cellulose synthase iso forms.