Nutrient depletion as a key factor for manipulating gene expression and product formation in different branches of the flavonoid pathway

Abstract

The content of flavonoids increases in response to nitrogen and phosphorus depletion in plants. Manipulation of these macronutrients may therefore be used to control the levels of desirable compounds and improve plant quality. Key enzymes in the shikimate pathway, which feeds precursors into the flavonoid pathway, are regulated post-translationally by feedback from aromatic amino acids, and possibly by redox control through photosynthesis. Use of microarrays for global transcript analysis in Arabidopsis has revealed that transcript levels are less influenced by mineral nutrients in the shikimate pathway compared with the flavonoid pathway. The responses in the shikimate pathway appear complex, whereas in the flavonoid pathway, a single gene often responds similarly to mineral depletion, high light intensity and sucrose. MYB [production of anthocyanin pigment 1 (PAP1)/production of anthocyanin pigment 2 (PAP2)] and bHLH [GLABRA3 (GL3)] transcription factors are important for the nutrient depletion response. PAP1/2 stimulate gross activation of the flavonoid pathway, and different investigations support merging signal transduction chains for various abiotic treatments on PAP1/2. Flavonol synthase is not part of the PAP1/2 regulon, and expression is mainly enhanced by high light intensity and sucrose, not mineral depletion. Nevertheless, both cyanidin and flavonol derivatives increase in response to nitrogen depletion. Kaempferols are the dominating flavonols in Arabidopsis leaves under normal cultivation conditions, but quercetin accumulation can be triggered by nitrogen depletion in combination with other abiotic factors.

Metabolomic and genetic analyses of flavonol synthesis in Arabidopsis thaliana support the in vivo involvement of leucoanthocyanidin dioxygenase

“…6a) indicates that LDOX can indeed exert FLS activity in the seedling. Thus, this is the Wrst direct evidence of in planta FLS activity of LDOX as suggested recently (Lillo et al 2008;Owens et al 2008a). The origin of the remaining very low amounts of Xavonol glycosides in the ldox Xs1-2 mutant remains unclear and the physiological relevance of these traces (undetectable with HPTLC, PDA-and UV-detectors) is questionable.…”

Integrating Plant Nutrients and Elicitors for Production of Secondary Metabolites, Sustainable Crop Production and Human Health: A Review

“…Nitrogen influences growth and morphological development (Gifford et al, 2008), primary and secondary plant metabolism (Giorgi et al, 2009). The link between primary and secondary metabolic pathways in plants is considered to occur through phenylalanine ammonia-lyase (PAL), which explains the concurrent increase of flavonoid activity with increased PAL activity (Lillo et al, 2008). Nitrogen is highly consumed by plants, and non-optimal concentrations of N can lead to losses of yield.…”

Is polyphenol induction simply a result of altered carbon and nitrogen accumulation?

“…[14][15][16] The relationship between nitrogen availability and phenolic synthesis is regulated at the transcriptional level. 17,18 A localized carbon excess relative to nutrient availabilities could result from many causes, including the impact of elevated light levels or CO 2 concentrations on photosynthesis, heterogeneous vascular connections or changing carbohydrate transport as leaves mature. 17,19,20 Since invertase activity is generally influenced by the same factors, 3 varying sink strength probably underlies such constitutive variation, which can be ecologically important.…”