Expression of a Zeatin-O-Glucoside-Degrading [beta]-Glucosidase in Brassica napus

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Abstract
A [beta]-glucosidase was purified from seeds of Brassica napus L. (oilseed rape). The 130-kD native enzyme consisted of a disulfide-linked dimer of 64-kD monomers. Internal amino acid sequences were used to construct degenerate primers for polymerase chain reaction-mediated cloning of cDNA for the enzyme. One nearly full-length and one partial [beta]-glucosidase-encoding cDNA clone were isolated and sequenced. Southern hybridization showed that [beta]-glucosidase is encoded by a small gene family in B. napus. Northern hybridization showed that the genes are expressed in the seed, with a low degree of expression in other tissues. In the seed, the expression started at 30 days after pollination (DAP), with the highest expression at 40 DAP. The size of the transcript was approximately 1900 nucleotides. In situ hybridization to developing seeds of B. napus showed that the [beta]-glucosidase expression started at 30 DAP around the provascular tissue in the embryo axis. In the cotyledons, mRNA initially accumulated around the provascular tissues but was detected first at 35 DAP. At 40 DAP, expression occurred in most parts of the seed. In situ hybridization also detected [beta]-glucosidase mRNA in shoots, young roots, and the basal part of the hypocotyls. Zeatin-O-glucoside was identified as a natural substrate for B. napus [beta]-glucosidase.