QT-GWAS:A novel method for unveiling biosynthetic loci affecting qualitative metabolic traits

Although the plant kingdom provides an enormous diversity of metabolites with potentially beneficial applications for humankind,a large fraction of these metabolites and their biosynthetic pathways remain unknown.Resolving metabolite structures and their biosynthetic pathways is key to gaining biological understanding andto allow metabolic engineering.In orderto retrieve novel biosynthetic genes involved in specialized metabolism,we developed a novel untargeted method designated as qualitative trait GWAs(QT-GWAS)that subjects qualitative metabolic traits to a genome-wide association study,while the conventional metabolite GWAS(mGWAS)mainly considers the quantitative variation of metabolites.As a proof of the validity of QT-GWAS,23 and 15of the retrieved associations identified in Arabidopsis thaliana by QTGWAS and mGWAS,respectively,were supported by previous research.Furthermore,seven genemetabolite associations retrieved by QT-GWAS were confirmed in this study through reverse genetics combined with metabolomics and/or in vitro enzyme assays.As such,we established that CYTOCHROME P450706A5(CYP706A5)is involved in the biosynthesis of chroman derivatives,UDP-GLYCOSYLTRANSFERASE 76C3(UGT76C3)is able tohexosylate guanine in vitro and in planta,and SULFOTRANSFERASE 202B1(SULT202B1)catalyzes the sulfation of neolignans in vitro.Collectively,our study demonstrates that the untargeted QT-GWAS method can retrieve valid gene-metabolite associations at the level of enzyme-encoding genes,even new associations that cannot be found by the conventional mGwAs,providing a new approach for dissecting qualitative metabolic traits.

Lignin engineering in forest trees: From gene discovery to field trials

Wood is an abundant and renewable feedstock for the production of pulp,fuels,and biobased materials.However,wood is recalcitrant toward deconstruction into cellulose and simple sugars,mainly because of the presence of lignin,an aromatic polymer that shields cell-wall polysaccharides.Hence,numerous research efforts have focused on engineering lignin amount and composition to improve wood processability.Here,we focus on results that have been obtained by engineering the lignin biosynthesis and branching pathways in forest trees to reduce cell-wall recalcitrance,including the introduction of exotic lignin monomers.In addition,we draw general conclusions from over 20 years of field trial research with trees engineered to produce less or altered lignin.We discuss possible causes and solutions for the yield penalty that is often associated with lignin engineering in trees.Finally,we discuss how conventional and new breeding strategies can be combined to develop elite clones with desired lignin properties.We conclude this review with priorities for the development of commercially relevant lignin-engineered trees.