A Novel Carotenoid-Derived Molecule Functions In Periodic Root Branching

Lateral root formation facilitates efficient exploration of the soil environment by a plant’s root system. In Arabidopsis, lateral roots are initiated when primordia form de novo within the primary root tissues. The formation of these primordia occurs in a shootward-to-rootward sequence and with a regular distribution. Using real-time imaging, we have shown that the sequential pattern of lateral roots is established by a periodic oscillation in gene expression near the root tip. Each oscillation results in a novel site, a prebranch site, at which a lateral root will ultimately form. These oscillating genes are hypothesized to comprise a lateral root clock that is part of the molecular mechanism regulating periodic lateral root formation. We find that carotenoid biosynthesis is required for the output of the lateral root clock, as carotenoid-deficient plants have disrupted oscillations in gene expression and a decreased number of sites competent to form lateral roots. Genetic and chemical inhibition of carotenoid biosynthesis indicates that developmental patterning of lateral roots requires a novel carotenoid-derived molecule.