Nucleotide diversity and linkage disequilibrium in Populus nigra cinnamyl alcohol dehydrogenase (CAD4) gene

Cinnamyl alcohol dehydrogenase (CAD) is involved in the biosynthesis of lignin, a component of plant cell wall which negatively impacts paper pulp processing and biomass fermentation to ethanol. Transgenic poplars with depressed CAD activity show structural alterations of lignin. Natural CAD mutants have been identified in several plants; however, no natural CAD mutants have been identified in poplar. We surveyed the natural genetic variation in CAD4, a gene coding for CAD, in 360 poplar trees from Western Europe. We measured linkage disequilibrium (LD) between single-nucleotide polymorphisms (SNPs), performed neutrality tests and estimated diversity indexes, and investigated their dependence from sample size. We identified 45 SNPs, six of which caused an amino acid substitution. Our results suggest a short span of LD in Populus nigra CAD4 gene. We identified carriers of different nonsynonymous SNPs in CAD4; those subjects are candidate to be used in classical breeding programs to obtain carriers of different combinations of functional polymorphisms. We showed that use of small sample size might lead to biased estimates of LD, neutrality tests, and diversity indexes. © 2011 Springer-Verlag.