GENETIC-ANALYSIS OF CINNAMYL ALCOHOL-DEHYDROGENASE IN LOBLOLLY-PINE -SINGLE-GENE INHERITANCE, MOLECULAR CHARACTERIZATION AND EVOLUTION

The gene encoding the monolignol biosynthetic enzyme cinnamyl alcohol dehydrogenase (CAD, E.C. 1.1.1.195) can be expressed in response to di fferent developmental and environmental cues. Control of Cad gene expr ession could involve either differential regulation of more than one C ad gene or, alternatively combinatorial regulation of a single Cad gen e. In loblolly pine (Pinus taeda L.), we found several electrophoretic variants (allozymes) of CAD and a high level of heterozygosity (h(e) = 0.46). Analysis of inheritance patterns of pine CAD allozymes gave s egregation ratios that were consistent with Mendelian expectations for a single functional gene. The identity of the full-length Cad cDNA se quence was confirmed by alignment with peptide sequences obtained from purified active enzyme and by extensive similarity to Cad sequences f rom other species. Southern blot analysis of genomic DNA using the Cad cDNA as a hybridization probe gave simple patterns, consistent with o ur interpretation that pine Cad is a single-copy gene. Phylogenetic an alysis and evolution rate estimates showed that Can sequences are dive rging less rapidly in the gymnosperms than in the angiosperms. The Cad mRNA was present in both lignifying tissues and a non lignifying tiss ue (the megagametophyte) of pine. The presence of a single gene sugges ts that different regulatory mechanisms for a single Cad gene, rather than differential regulation of several genes, can account for its exp ression in response to different cues.