Two a-L-arabinofuranosidase genes in Arabidopsis thaliana are differentially expressed during vegetative growth and ̄ower development*

Glycosyl hydrolases are important mediators of plant cell wall modi®cation during plant development. These enzymes catalyse the hydrolytic release of speci®c sugars, such as L-arabinose, from the polysaccharide-rich cell wall matrix. The cloning and expression analysis of two genes, AtASD1 and AtASD2, encoding putative a-L-arabinofuranosidases in Arabidopsis thaliana are reported here. AtASD1 and AtASD2 identities were assigned on the basis of homology to plant and microbial family 51 glycoside hydrolases. Using RT-PCR, RNA gel blot analysis and reporter gene expression analysis, AtASD1 and AtASD2 were shown to have different developmental expression pro®les. High levels of AtASD1 promoter activity are present in multiple tissues during vegetative and reproductive growth. AtASD1 expression is particularly intense in zones of cell proliferation, the vascular system, developing and regressing ̄oral tissues, and ̄oral abscission zones. By comparison, AtASD2 expression is limited to the vasculature of older root tissue and to some ̄oral organs and ̄oral