Plant Genome III Conference

MOLECULAR CHARACRERIZATION OF UBIQUITOUS B-AMYLASE IN BARLEY (Hordeum vulgare L.)

B-amylase activity is an important component of barley malting quality. Malting quality QTL effects were mapped to chromosomes 2 and 4, in the vicinity of two B-amylase loci. In an effort to characterize the molecular basis of the observed QTL effects, we have isolated a 1812-bp cDNA clone that encodes ubiquitous B-amylase from an ovary cDNA library of the malting cultivar 'Morex'. Unlike the previously-reported barley B-amylase clones (Kreis et al., 1987; Yoshigi et al., 1994), the ubiquitous B-amylase has no glycine-rich repeats in the C-terminus. An 80% homology was observed between the ubiquitous B-amylase clone and the previously-reported clones at the amino acid level. Using transcript-specific probes derived from the non-homologous sequences in the 3'regions we have determined that the ubiquitous B-amylase is encoded by the B-amylase locus in barley chromosome 2 and the previously-reported B-amylase is encoded by the locus in the minus arm of chromosome 4. More restriction fragment length polymorphisms were detected in the chromosome 4 locus. Elevated transcript levels of the ubiquitous B-amylase were observed in early embryogenesis. Transcripts of the previously reported B-amylase were detected only at a late stage of seed maturation in Northern blots. Therefore the previously reported clones may represent the late endosperm-specific B-amylase in barley.