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Biochemical and genetic analyses have previously identified caffeoyl shikimate esterase ( CSE) as an enzyme in the monolignol biosynthesis pathway in Arabidopsis thaliana, although the generality of this finding has been questioned. Here we show the presence of CSE genes and associated enzyme activity in barrel medic ( Medicago truncatula, dicot, Leguminosae), poplar ( Populus deltoides, dicot, Salicaceae), and switchgrass ( Panicum virgatum, monocot, Poaceae). Loss of function of CSE in transposon insertion lines of M. truncatula results in severe dwarfing, altered development, reduction in lignin content, and preferential accumulation of hydroxyphenyl units in lignin, indicating that the CSE enzyme is critical for normal lignification in this species. However, the model grass Brachypodium distachyon and corn ( Zea mays) do not possess orthologs of the currently characterized CSE genes, and crude protein extracts from stems of these species exhibit only a weak esterase activity with caffeoyl shikimate. Our results suggest that the reaction catalyzed by CSE may not be essential for lignification in all plant species. [ABSTRACT FROM AUTHOR]

It is necessary to overcome recalcitrance of the biomass to saccharification (sugar release) to make switchgrass (Panicum virgatum) economically viable as a feedstock for liquid biofuels. Lignin content correlates negatively with sugar release efficiency in switchgrass, but selecting the right gene candidates for engineering lignin biosynthesis in this tetraploid outcrossing species is not straightforward. To assist this endeavor, we have used an inducible switchgrass cell suspension system for studying lignin biosynthesis in response to exogenous brassinolide. By applying a combination of protein sequence phylogeny with whole-genome microarray analyses of induced cell cultures and developing stem internode sections, we have generated a list of candidate monolignol biosynthetic genes for switchgrass. Several genes that were strongly supported through our bioinformatics analysis as involved in lignin biosynthesis were confirmed by gene silencing studies, in which lignin levels were reduced as a result of targeting a single gene. However, candidate genes encoding enzymes involved in the early steps of the currently accepted monolignol biosynthesis pathway in dicots may have functionally redundant paralogues in switchgrass and therefore require further evaluation. This work provides a blueprint and resources for the systematic genome-wide study of the monolignol pathway in switchgrass, as well as other C4 monocot species. [ABSTRACT FROM AUTHOR]

Abstract: (Iso)flavonoids are a diverse group of plant secondary metabolites with important effects on plant, animal and human health. They exist in various glycosidic forms. Glycosylation, which may determine their bioactivities and functions, is controlled by specific plant uridine diphosphate glycosyltransferases (UGTs). We describe a new multifunctional (iso)flavonoid glycosyltransferase, UGT85H2, from the model legume Medicago truncatula with activity towards a number of phenylpropanoid-derived natural products including the flavonol kaempferol, the isoflavone biochanin A, and the chalcone isoliquiritigenin. The crystal structure of UGT85H2 has been determined at 2.1 Å resolution, and reveals distinct structural features that are different from those of other UGTs and related to the enzyme''s functions and substrate specificities. Structural and comparative analyses revealed the putative binding sites for the donor and acceptor substrates that are located in a large cleft formed between the two domains of the enzyme, and indicated that Trp360 may undergo a conformational change after sugar donor binding to the enzyme. UGT85H2 has higher specificity for flavonol than for isoflavone. Further substrate docking combined with enzyme activity assay and kinetic analysis provided structural insights into this substrate specificity and preference. [Copyright &y& Elsevier]