Flavonols regulate root light avoidance response and root growth

The CBGP Group ‘Regulation of Lateral Root Development’ has identified the molecular mechanisms used by roots to escape from sunlight and the role of flavonols in integrating hormonal signaling and ROS (reactive oxygen species) to control the balance between cell proliferation and differentiation.

Roots normally grow in the darkness, but under some circumstances they may be exposed to sunlight. In such cases, after perceiving light, roots bend to escape from light (also known as root light avoidance) to continuing to explore the soil. However, if the illumination persists thus generating a non-friendly environment, roots reduce their growth. Traditionally, model plants such as Arabidopsis, have been grown in vitro illuminating the root, a condition that alters their development and responses. Recently, we have engineered a new system (D-Root) to grow the root system in darkness and the shoot in presence of under light (Silva-Navas et al., 2015). Using this device we have found that flavonols, a family of secondary metabolites, regulate the root light avoidance in Arabidopsis. Flavonols preferentially accumulate on the illuminated side of the root, favoring cell elongation. This higher rate of elongation forms a root curvature, which needs to escape from the light source. Likewise, flavonols integrate different hormonal signal (auxin and cytokinin) and ROS to regulate the balance of cell division/differentiation/elongation at the root tip and to stablish the different root growth zones. Thus, roots illuminated for a long period of time accumulate high level of flavonols that repress cell proliferation and root growth.