Molecular analysis of the alcohol dehydrogenase gene family of barley

One partial and two complete genomic clones of the three loci specifying alcohol dehydrogenase (ADH) in barley were isolated by screening libraries with a maize Adh1 cDNA probe. Each gene is characterised by an intron arrangement similar to that of both maize Adh1 and Adh2, although two genes show an exon fusion. A comparison with the maize coding sequences unambiguously assorts the barley loci into an Adh1-like gene and two Adh2-like genes, indicating that an ancient gene duplication underlies the widespread occurrence of two Adh loci in higher plants. In the barley lineage there has been a further duplication-transposition of a progenitor "Adh2" locus to give rise to the extant three-gene system, with gene copies of different ancestry being closely linked. An Adh1 null-allele, Adh1-M9, has been cloned; the available sequence includes an intron with a missing acceptor splice signal. Two independent clones of one of the barley Adh2-like genes have an 18 bp in-frame deletion towards the 3' end of the coding sequence. The barley Adh2-like genes are extensively diverged in their 5' sequences apart from a conserved 15 bp motif in the mRNA leader region and sequences at the start of transcription. A sequence related to the hexanucleotide core of a regulatory element found in maize Adh1 and in other anaerobically induced plant genes is present in the 5' region of barley Adh2.