INHERITANCE, GENE-EXPRESSION, AND LIGNIN CHARACTERIZATION IN A MUTANTPINE DEFICIENT IN CINNAMYL ALCOHOL-DEHYDROGENASE

We have discovered a mutant loblolly pine (Pinus taeda L.) in which ex pression of the gene encoding cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) is severely reduced, The products of CAD, cinnamyl alcohols , are the precursors of lignin, a major cell wall polymer of plant vas cular tissues, Lignin composition in this mutant shows dramatic modifi cations, including increased incorporation of the substrate of CAD (co niferaldehyde), indicating that CAD may modulate lignin composition in pine. The recessive cad-n1 allele, which causes this phenotype, was d iscovered in a tree heterozygous for this mutant allele, It is inherit ed as a simple Mendelian locus that maps to the same genomic region as the end locus, In mutant plants, CAD activity and abundance of end RN A transcript are low, and free CAD substrate accumulates to a high lev el, 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 c omposition of lignin varies beyond previous expectations still provide s vascular function and mechanical support.