Genome-Wide Analyses Of The Ten Multigene Families Involved In The Eucalyptus grandis Phenylpropanoid Metabolism and Lignin Branch Pathway

The phenolic polymer lignin is a major component of wood fulfilling important biological roles in trees. Eucalyptus grandis and E. globulus hold a substantial economic importance for the wood industry. The recent availability of the full sequenced genome of Eucalyptus grandisprovided research opportunities to decipher the biosynthesis of lignin monomers which comprises ten enzymatic reactions catalyzed by enzymes encoded by ten multigene families

We performed a genome-wide survey of these E. grandis multigene families, and conducted comparative phylogenetic analyses by including bona fide lignin-biosynthetic genes from other species. We surveyed the expression profiles of all families’ members through RNAseq in six E grandis tissues and, for a subset of putative bona fide lignin-biosynthetic genes, by RT-qPCR in a large panel of 16 E. globulustissues.

We identified 174 genes scattered all over the eleven E. grandis chromosomes. In the four largest families (COMT, CAD, CCoAOMT and PAL), tandem gene duplication was found to be a preeminent mechanism explaining their significant expansion in comparison to other plant species. Expression profiling evidenced that the subset of genes exhibiting strong, preferential expression in highly lignified tissues, integrate vascular lignification bona fidephylogenetic clades which were found not expanded.

The combination of phylogeny and expression analyses allowed us to define a Eucalyptus lignin toolbox featuring 24 members, representing all ten multigene families. In addition, we identified five new genes outside the bona fide clades, highly or preferentially expressed in xylem, whose function merits to be studied through gain and loss of function studies.