Characterization of a maize beta-amylase cDNA clone and its expression during seed germination.

摘要

A cDNA clone (pZMB2) encoding beta-amylase was isolated from a cDNA library prepared from the aleurone RNA of germinating maize cv. TN351 kernels. The cDNA encodes a predicted product of 488 amino acids with significant similarity to known beta-amylases from barley, rye, and rice. Glycine-rich repeats found in the carboxyl terminus of the endosperm-specific beta-amylase of barley and rye were absent from the maize gene product. The N-terminal sequence of the first 20 amino acids of a beta-amylase peptide derived from purified protein was identical from the 5th to the 24th amino acids of the predicted cDNA product, indicating the absence of a conventional signal peptide in the maize protein. Recombinant inbred mapping data indicate that the cDNA clone is a single-copy gene that maps to chromosome 7L at position 83 centimorgans. Northern blot analysis and in vitro translation-immunoprecipitation data indicate that the maize beta-amylase is synthesized de novo in the aleurone cells but not in the scutellum during seed germination. The maize beta-amylase cDNA sequence reported can be found under GenBank accession number Z25871.