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Inheritance, gene expression, and lignin characterization in a mutant pine deficient in cinnamyl alcohol dehydrogenase

MacKay, J.J., O'Malley, D.M., Presnell, T., Booker, F.L., Campbell, M.M., Whetten, R.W., Sederoff, R.R.
Proceedings of the National Academy of Sciences of the United States of America 1997 v.94 no.15 pp. 8255-8260
Pinus taeda, mutants, alleles, alcohol oxidoreductases, loci, gene expression, messenger RNA, chromosome mapping, genetic markers, wood, color, lignin, phenolic compounds, enzyme activity, inheritance (genetics), random amplified polymorphic DNA technique, phenotype, chemical constituents of plants
We have discovered a mutant loblolly pine (Pinus taeda L.) in which expression of the gene encoding cinnamyl alcohol dehydrogenase (CAD; EC is severely reduced. The products of CAD, cinnamyl alcohols, are the precursors of lignin, a major cell wall polymer of plant vascular tissues. Lignin composition in this mutant shows dramatic modifications, including increased incorporation of the substrate of CAD (coniferaldehyde), indicating that CAD may modulate lignin composition in pine. The recessive cad-n1 allele, which causes this phenotype, was discovered in a tree heterozygous for this mutant allele. It is inherited as a simple Mendelian locus that maps to the same genomic region as the cad locus. In mutant plants, CAD activity and abundance of rod RNA transcript are low, and free CAD substrate accumulates to a high level. The wood of the mutant is brown, whereas the wood in wild types is nearly white. The wood phenotype resembles that of brown midrib (bm) mutants and some transgenic plants in which xylem is red-brown due to a reduction in CAD activity. However, unlike transgenics with reduced CAD, the pine mutant has decreased lignin content. Wood in which the composition of lignin varies beyond previous expectations still provides vascular function and mechanical support.