The Arabidopsis At1g45130 and At3g52840 genes encode beta-galactosidases with activity toward cell wall polysaccharides.

The Arabidopsis genes At1g45130 and At3g52840 encode the beta-galactosidase isozymes Gal-5 and Gal-2 that belong to Glycosyl Hydrolase Family 35 (GH 35). The two enzymes share 60% sequence identity with each other and 38-81% with other plant beta-galactosidases that are reported to be involved in cell wall modification. We studied organ-specific expression of the two isozymes. According to our western blot analysis using peptide-specific antibodies, Gal-5 and Gal-2 are most highly expressed in stem and rosette leaves. We show by dot-immunoblotting that Gal-5 and Gal-2 are associated with the cell wall in Arabidopsis. We also report expression of the recombinant enzymes in P. pastoris and describe their substrate specificities. Both enzymes hydrolyze the synthetic substrate para-nitrophenyl-beta-d-galactopyranoside and display optimal enzyme activity between pH 4.0 and 4.5, similar to the pH optimum reported for other well-characterized plant beta-galactosidases. Both Gal-5 and Gal-2 show a broad specificity for the aglycone moiety and a strict specificity for the glycone moiety in that they prefer galactose and its 6-deoxy analogue, fucose. Both enzymes cleave beta-(1,4) and beta-(1,3) linkages in galacto-oligosaccharides and hydrolyze the pectic fraction of Arabidopsis cell wall. These findings suggest that Gal-5 and Gal-2 could be involved in the modification of cell wall polysaccharides.

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