Jj. Mackay et al., INHERITANCE, GENE-EXPRESSION, AND LIGNIN CHARACTERIZATION IN A MUTANTPINE DEFICIENT IN CINNAMYL ALCOHOL-DEHYDROGENASE, Proceedings of the National Academy of Sciences of the United Statesof America, 94(15), 1997, pp. 8255-8260
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.