Christopher S. Bond Life Sciences Center, University of Missouri,
Columbia, MO, USA
ORCiD: 0000-0003-1092-9393
Keywords: Populus trichocarpa , GWAS, lignin, laccase,
saccharification, cell wall recalcitrance.
Lignin is a major biopolymer found in nature, especially in woody plant
cell walls, with important economic implications for papermaking and
biorefining industries. Natural genetic diversity within plant species
can be used as a valuable resource in genome-wide association studies
(GWAS) for identifying genes that contribute to phenotypic variation in
physiological traits. In this study, we measured lignin amount and
composition by thioacidolysis GC-MS in developing xylem samples from 433
individuals of a Populus trichocarpa population distributed along
the Northwest coast of North America. Whole-genome resequencing data of
these trees, coupled with multitrait association analyses, were used to
detect genes underlying the variation in lignin amount and monomer
composition. A subgroup of individuals with phenotypically extreme
lignin composition was selected for further gene expression analyses and
saccharification assays. Our results show a wide variation in the two
major monolignols (G and S) among natural poplar variants. In addition
to association with the biosynthetic gene Ferulate-5-Hydroxylase (F5H),
we found that the polymerization of lignin by laccases (Lac) has a major
role driving the lignin composition changes observed, with PtLac4 and
PtLac17 displaying higher affinity for sinapyl alcohol as substrate.
Furthermore, trees with extreme S/G ratios displayed different gene
expression patterns and cell wall saccharification efficiency for
biofuel production. Our work expands our knowledge on the regulation of
lignin composition in trees and paves the way to generate natural
biopolymers and high value chemicals from poplar.