Flavonols modulate lateral root emergence by scavenging reactive oxygen species in Arabidopsis thaliana

Abstract

Flavonoids are a class of specialized metabolites with subclasses including flavonols and anthocyanins, which have unique properties as antioxidants. Flavonoids modulate plant development, but whether and how they impact lateral root development is unclear. We examined potential roles for flavonols in this process using Arabidopsis thaliana mutants with defects in genes encoding key enzymes in flavonoid biosynthesis. We observed the tt4 and fls1 mutants, which produce no flavonols, have increased lateral root emergence. The tt4 root phenotype was reversed by genetic and chemical complementation. To more specifically define the flavonoids involved, we tested an array of flavonoid biosynthetic mutants, eliminating roles for anthocyanins and the flavonols quercetin and isorhamnetin in modulating lateral root development. Instead, two tt7 mutant alleles, with defects in a branchpoint enzyme blocking quercetin biosynthesis, formed reduced numbers of lateral roots and tt7-2 had elevated levels of kaempferol. Using a flavonol-specific dye, we observed that in the tt7-2 mutant, kaempferol accumulated within lateral root primordia at higher levels than wild-type. These data are consistent with kaempferol, or downstream derivatives, acting as a negative regulator of lateral root emergence. We examined ROS accumulation using ROS-responsive probes and found reduced fluorescence of a superoxide-selective probe within the primordia of tt7-2 compared with wild-type, but not in the tt4 mutant, consistent with opposite effects of these mutants on lateral root emergence. These results support a model in which increased level of kaempferol in the lateral root primordia of tt7 -2 reduces superoxide concentration and ROS-stimulated lateral root emergence.

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

“…Firstly, flavonoids have antioxidative properties ( Agati et al, 2012 ) and impaired biosynthesis of flavonoids results in higher reactive oxygen species (ROS) levels in the plant ( Watkins et al, 2014 ; Gayomba and Muday, 2020 ). For example, the flavonoid kaempferol was described as a negative regulator of lateral root growth, most likely by regulating ROS levels in the lateral root primordia ( Chapman and Muday, 2021 ). Secondly, the flavonoids naringenin, quercetin, and kaempferol have also been described to be auxin transport inhibitors ( Jacobs and Rubery, 1988 ; Brunn et al, 1992 ; Faulkner and Rubery, 1992 ) and endogenous over- or underproduction of flavonoids was shown to influence auxin transport using mutants in the flavonoid biosynthetic pathway ( Murphy et al, 2000 ; Brown et al, 2001 ; Peer et al, 2004 ; Buer et al, 2013 ).…”

Arbuscular mycorrhizal symbiosis enhances tomato lateral root formation by modulating CEP2 peptide expression

“…Roots were stained with Trypan Blue, and fungal colonization levels were quantified with a modified gridline intersect procedure as described previously (Paszkowski et al ., 2006). To observe unemerged LR primordia (LRPs), roots were treated with Clearsee solution according to the published protocol followed by 1% safranin‐O staining (Chapman & Muday, 2021).…”

The Flavonoid Biosynthesis Network in Plants

“…F3′H can also catalyze the conversion of kaempferol to quercetin, while F3′5′H activity generates myricetin from kaempferol or quercetin [ 108 ]. Kaempferol, quercetin, and myricetin are further modified to various flavonol derivatives through the activities of enzymes such as methyl transferases, GTs, and acyltransferase (AT), among others [ 60 , 109 ]. FLS, a FeⅡ/2-oxoglutarate-dependent dioxygenase, is the key and rate-limiting enzyme in the flavonol biosynthesis pathway [ 110 ] and catalyzes the desaturation of dihydroflavonol to form a C-2 and C-3 double bond in ring C [ 111 ].…”