1.
Suppression of UV-B stress induced flavonoids by biotic stress: Is there reciprocal crosstalk?
Schenke, D, Utami, HP, Zhou, Z, Gallegos, MT, Cai, D
Plant physiology and biochemistry : PPB. 2019;:53-63
Abstract
Plants respond to abiotic UV-B stress with enhanced expression of genes for flavonoid production, especially the key-enzyme chalcone synthase (CHS). Some flavonoids are antioxidative, antimicrobial and/or UV-B protective secondary metabolites. However, when plants are challenged with concomitant biotic stress (simulated e.g. by the bacterial peptide flg22, which induces MAMP triggered immunity, MTI), the production of flavonoids is strongly suppressed in both Arabidopsis thaliana cell cultures and plants. On the other hand, flg22 induces the production of defense related compounds, such as the phytoalexin scopoletin, as well as lignin, a structural barrier thought to restrict pathogen spread within the host tissue. Since all these metabolites require the precursor phenylalanine for their production, suppression of the flavonoid production appears to allow the plant to focus its secondary metabolism on the production of pathogen defense related compounds during MTI. Interestingly, several flavonoids have been reported to display anti-microbial activities. For example, the plant flavonoid phloretin targets the Pseudomonas syringae virulence factors flagella and type 3 secretion system. That is, suppression of flavonoid synthesis during MTI might have also negative side-effects on the pathogen defense. To clarify this issue, we deployed an Arabidopsis flavonoid mutant and obtained genetic evidence that flavonoids indeed contribute to ward off the virulent bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. Finally, we show that UV-B attenuates expression of the flg22 receptor FLS2, indicating that there is negative and reciprocal interaction between this abiotic stress and the plant-pathogen defense responses.
2.
Flavonoids and the gastrointestinal tract: Local and systemic effects.
Oteiza, PI, Fraga, CG, Mills, DA, Taft, DH
Molecular aspects of medicine. 2018;:41-49
Abstract
The gastrointestinal (GI) tract plays a central role in the absorption, distribution, metabolism, and excretion of flavonoids, which ultimately define the health effects of these bioactives. These aspects are modulated by the interactions of flavonoids with other dietary components, environmental factors, the host, and the GI microbiota. Flavonoid can target molecules in the luminal content, the different GI tract cell types, and the microbiota. Importantly, flavonoid actions at the GI tract can have an impact systemically, e.g. on glucose homeostasis, lipid and energy metabolism, or cardiovascular risk factors. The beneficial actions of flavonoids at the GI include their capacity to: i) protect the intestinal epithelium against pharmacological insults and food toxins; ii) modulate the activity of enzymes involved in lipid and carbohydrate absorption; iii) maintain the intestinal barrier integrity; iv) modulate the secretion of gut hormones; v) modulate the GI tract immune system; vi) exert potential anti-colorectal cancer activity; and vii) shape microbiota composition and function. Further understanding of the mechanisms mediating the effects of flavonoids on the intestine (and its microbiota) is of critical importance given the relevance of the GI tract on sustaining overall health and of the widespread recommendations of increasing the intake of plant bioactives.