Regulation of genes encoding beta-D-glucan glucohydrolases in barley (Hordeum vulgare)

Expression patterns of barley beta -D-glucan glucohydrolase genes were moni tored using cDNAs encoding isoenzymes ExoI and ExoII. The cDNAs were isolat ed from 5-day-old seedling libraries. The enzymes are encoded by a small ge ne family, in which marked differences in codon usage are evident. The cDNA s can be used as specific probes for two subfamilies of beta -D-glucan gluc ohydrolase genes. Genes of both subfamilies are transcribed in the scutellu m of germinated grain, in elongating coleoptiles, and in young roots and le aves. Low levels of mRNA for the isoenzyme ExoI gene subfamily could be det ected in aleurone layers of germinated grain. Most of the beta -D-glucan gl ucohydrolase activity can be extracted from tissues with dilute aqueous buf fers. Enzyme activity is highest in young leaves and elongating coleoptiles , but is not well-correlated with mRNA levels. The expression patterns are consistent with proposed roles for beta -glucan glucohydrolases in the turn over or modification of cell-wall (1 --> 3,1 --> 4)-beta -D-glucans in elon gating coleoptiles; and in young vegetative tissues.