Glucosinolate and phenylpropanoid biosynthesis are linked by proteasome‐dependent degradation of PAL

Abstract

Summary Plants produce several hundreds of thousands of secondary metabolites that are important for adaptation to various environmental conditions. Although different groups of secondary metabolites are synthesized through unique biosynthetic pathways, plants must orchestrate their production simultaneously. Phenylpropanoids and glucosinolates are two classes of secondary metabolites that are synthesized through apparently independent biosynthetic pathways. Genetic evidence has revealed that the accumulation of glucosinolate intermediates limits phenylpropanoid production in a Mediator Subunit 5 (MED5)‐dependent manner. To elucidate the molecular mechanism underlying this process, we analyzed the transcriptomes of a suite of Arabidopsis thaliana glucosinolate‐deficient mutants using RNAseq and identified misregulated genes that are rescued by the disruption of MED5. The expression of a group of Kelch Domain F‐Box genes (KFBs) that function in PAL degradation is affected in glucosinolate biosynthesis mutants and the disruption of these KFBs restores phenylpropanoid deficiency in the mutants. Our study suggests that glucosinolate/phenylpropanoid metabolic crosstalk involves the transcriptional regulation of KFB genes that initiate the degradation of the enzyme phenylalanine ammonia‐lyase, which catalyzes the first step of the phenylpropanoid biosynthesis pathway. Nevertheless, KFB mutant plants remain partially sensitive to glucosinolate pathway mutations, suggesting that other mechanisms that link the two pathways also exist.

Aldoxime Metabolism Is Linked to Phenylpropanoid Production in Camelina sativa

“…In Arabidopsis, the accumulation of IAOx or its derivatives enhances the expression of these four KFBs and in turn, results in reduced PAL activity and phenylpropanoid production (Kim et al, 2019). When AtKFBs are disrupted in high aldoximecontaining mutants, phenylpropanoid deficiency is restored (Kim et al, 2019). Thus, we hypothesized that a similar mechanism may function in the repression of PAL in C. sativa.…”

“…These KFBs are components of ubiquitin E3 ligase, and AtKFB1, AtKFB20, AtKFB39, and AtKFB50 facilitate ubiquitination of PAL redundantly (Zhang et al, 2013;Zhang et al, 2015). In Arabidopsis, the accumulation of IAOx or its derivatives enhances the expression of these four KFBs and in turn, results in reduced PAL activity and phenylpropanoid production (Kim et al, 2019). When AtKFBs are disrupted in high aldoximecontaining mutants, phenylpropanoid deficiency is restored (Kim et al, 2019).…”

“…Although each metabolite is produced through its respective biosynthetic pathway, plants orchestrate multiple biosynthetic pathways simultaneously. Recent studies have shown the influence of glucosinolate intermediates on phenylpropanoid production (Hemm et al, 2003;Kim et al, 2015;Kim et al, 2019).…”

“…The steady state phenylalanine pools in ref5 mutants were higher than that in the wild type suggesting that the inhibition may occur at or downstream of PAL in the phenylpropanoid biosynthetsis pathway (Kim et al, 2015). A transcriptome study with a set of glucosinolate-deficient mutants identified that there are MED5-dependent and MED5-independent mechanisms behind the crosstalk, and that the increased levels of aldoximes up-regulate kelch-domain containing F-box genes functioning in the ubiquitination of PALs (Kim et al, 2019).…”

A noninvasive, machine learning–based method for monitoring anthocyanin accumulation in plants using digital color imaging

“…RMSE = root mean squared error; MAE = mean average error. stability of phenylalanine ammonia lyase (PAL) functioning at the first step of the phenylpropanoid pathway in these mutants; as a result, ref2 contains a reduced level of phenylpropanoids, including anthocyanin, while b2b3 accumulates more phenylpropanoids than the wild type (Kim et al, 2015(Kim et al, , 2019. Because the Col-0, pap1-D, ref2, and b2b3 genotypes accumulate different levels of anthocyanin under nonstressed conditions, we were able to consistently generate Arabidopsis plants with a broad range of anthocyanin contents without the use of additional stress treatments ( Fig.…”