Behind the Scenes: The Impact of Bioactive Phenylpropanoids on the Growth Phenotypes of Arabidopsis Lignin Mutants

Abstract

The phenylpropanoid pathway converts the aromatic amino acid phenylalanine into a wide range of secondary metabolites. Most of the carbon entering the pathway incorporates into the building blocks of lignin, an aromatic polymer providing mechanical strength to plants. Several intermediates in the phenylpropanoid pathway serve as precursors for distinct classes of metabolites that branch out from the core pathway. Untangling this metabolic network in Arabidopsis was largely done using phenylpropanoid pathway mutants, all with different degrees of lignin depletion and associated growth defects. The phenotypic defects of some phenylpropanoid pathway mutants have been attributed to differentially accumulating phenylpropanoids or phenylpropanoid-derived compounds. In this perspectives article, we summarize and discuss the reports describing an altered accumulation of these bioactive molecules as the causal factor for the phenotypes of lignin mutants in Arabidopsis.

Non-specific effects of a CINNAMATE-4-HYDROXYLASE inhibitor on auxin homeostasis

“…Accordingly, plants are equipped with a range of enzymes that mediate the conjugation and/or sequestration of these compounds, such as UDP-glycosyltransferases (UGTs), glutathione-S-transferases (GSTs) and amido synthetases (Schröder and Collins 2002;Casanova-Sáez et al 2021). For example, the glycosylation of several phenylpropanoids allows for the regulation of their endogenous levels via sequestration to the vacuole (Dima et al 2015;Le Roy et al 2016), a mechanism which is proposed to mitigate the toxicity of bioactive phenylpropanoid accumulation (Le Roy et al 2016;Vanholme et al 2019;El Houari et al 2021a;Steenackers et al 2019).…”

Friends in Arms: Flavonoids and the Auxin/Cytokinin Balance in Terrestrialization

“…p -coumaryl-CoA is also converted into p -coumaraldehyde by the enzyme cinnamoyl-CoA reductase or into caffeic acid by p -coumarate 3-hydroxylase. Both compounds are precursors for the phenylpropanoid monomers that make up lignin [ 31 ]. Several gold-standard reviews comprehensively discuss phenylpropanoid and flavonoid biosynthetic pathways, their regulation, and species-specific distributions of different phenylpropanoid species [ 27 , 30 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ].…”

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

“…For example, the Arabidopsis ref3 mutant accumulates high levels of cinnamate-derived compounds owing to its reduced C4H activity. Cinnamate hyperaccumulation in ref3 mutants impairs auxin signaling, which might underlie the observed yield penalty ( Schilmiller et al., 2009 ; Steenackers et al., 2019 ; El Houari et al., 2021 ). Arabidopsis and Medicago HCT -deficient plants accumulate high levels of the stress hormone salicylic acid (SA), which negatively influences stem height in the transgenic plants ( Gallego-Giraldo et al., 2011a ).…”