Cell wall modifications triggered by the down-regulation of Coumarate 3-hydroxylase-1 in maize

Abstract

Coumarate 3-hydroxylase (C3H) catalyzes a key step of the synthesis of the two main lignin subunits, guaiacyl (G) and syringyl (S) in dicotyledonous species. As no functional data are available in regards to this enzyme in monocotyledonous species, we generated C3H1 knockdown maize plants. The results obtained indicate that C3H1 participates in lignin biosynthesis as its down-regulation redirects the phenylpropanoid flux: as a result, increased amounts of phydroxyphenyl (H) units, lignin-associated ferulates and the flavone tricin were detected in transgenic stems cell walls. Altogether, these changes make stem cell walls more degradable in the most C3H1-repressed plants, despite their unaltered polysaccharide content. The increase in H monomers is moderate compared to C3H deficient Arabidopsis and alfalfa plants. This could be due to the existence of a second maize C3H protein (C3H2) that can compensate the reduced levels of C3H1 in these C3H1-RNAi maize plants. The reduced expression of C3H1 alters the macroscopic phenotype of the plants, whose growth is inhibited proportionally to the extent of C3H1 repression. Finally, the down-regulation of C3H1 also increases the synthesis of flavonoids, leading to the accumulation of anthocyanins in transgenic leaves.

Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

“…Such a redirection of the flux would have a particularly strong effect in the C2 background that has a high flux toward flavonoids. Recently, it was reported that stems of C3H1-RNAi (for RNA interference) maize plants (which produce less lignin) have increased levels of tricin, consistent with a redirection of the carbon flux to the synthesis of flavonoids instead of the canonical monolignols (Fornalé et al, 2015). In the leaves of maize C2-Idf mutants, the reverse takes place: a substantial redirection of the carbon flux from the biosynthesis of flavonoids to the biosynthesis of the canonical monolignols.…”

Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility

“…5E). It has been reported that disruptions in the monolignol biosynthetic pathway redirect the metabolic flux in the phenylpropanoid pathway and occasionally affect accumulations of flavonoids (Abdulrazzak et al, 2006;Besseau et al, 2007;Fornalé et al, 2010;Li et al, 2010;Vanholme et al, 2012;Fornalé et al, 2015). Therefore, it is conceivable that a blockage in a flavonoid pathway may, in turn, affect the generation of monolignols and their lignin polymers.…”

“…Subsequently, extensive surveys have revealed that tricin-bound lignins exist abundantly, particularly in the monocot family Poaceae, which comprises grasses including cereals. They also have been found in some commelinid monocot families outside Poaceae, such as Arecaceae (palms) and Bromeliaceae (pineapples and relatives), the noncommelinid family Orchidaceae (the orchids), particularly in the genus Vanilla, and also in certain dicots (Rencoret et al, 2013;Wen et al, 2013;Del Río et al, 2015;Lan et al, 2015Lan et al, , 2016aLan et al, , 2016bKoshiba et al, 2017).…”

Transcriptome Profiling of Tomato Uncovers an Involvement of Cytochrome P450s and Peroxidases in Stigma Color Formation

“…Moreover, the two CYP450 genes were also involved in the “Flavonoid biosynthesis” pathway (Supplementary Table S8). In these pathways, the two CYP450 genes encoded the C3H which catalyze the p -coumaric acid, p -coumaroyl-CoA and p -coumaraldehyde to caffeic acid, caffeoyl-CoA and caffeyl aldehyde, respectively ( Figure 6 and Supplementary Figure S2) (Xue et al, 2014; Fornaléa et al, 2015), so, we named these two genes as SlC3H1 ( Solyc10g078220 ) and SlC3H2 ( Solyc10g078230 ). In addition, the six POD genes were involved in the last step of biosynthesis of lignin, an insoluble cell wall-associated polymer ( Figure 6 ) (Quiroga et al, 2000; Higuchi, 2006).…”