A Genetic Approach to Understanding the Roles of Flavonols in Tomato Root Development

The flavonoid biosynthetic pathway produces a number of important plant specialized metabolites, including flavonols, which are known for their antioxidant properties. Using a collection of tomato mutants with defects in genes encoding enzymes in the flavonoid biosynthesis pathway, we are examining the role of flavonols in modulating root development and asking whether these effects are orchestrated through the scavenging of reactive oxygen species (ROS). We used mutants whose defects alter accumulation of one or more of the flavonols: kaempferol, quercetin, isorhamnetin, and myricetin, listed in order of synthesis by the pathway. The mutant anthocyanin reduced (are), which has an early pathway defect, has decreased levels of flavonols as detected by liquid chromatography mass spectrometry (LCMS). The are mutant has reduced lateral root number and increased root hair number consistent with previous data showing flavonol accumulation at sites of LR development in wild-type using DPBA. This mutant also has elevated levels of ROS in roots detected using DCF, a general ROS sensor, consistent with flavonols modulating root architecture by altering the levels of reactive oxygen species. In contrast, anthocyanin without (aw) has a defect in the pathway after flavonol synthesis resulting in elevated levels of kaempferol and quercetin and has an increased number of lateral roots as compared to wild type. The mutant anthocyaninless (a) has a defect in the enzyme that produces myricetin, and has increased levels of kaempferol, quercetin, and isorhamnetin and decreased levels of myricetin, resulting in increased lateral roots as compared to wild-type. These results indicate that M does not play a role in the regulation of lateral root development, but that are consistent with kaempferol or quercetin-modulated ROS accumulation regulating root development. This work was supported by AFRI Grant 2016-0579 from the USDA NIFA.