Exogenous application of the apocarotenoid retinaldehyde negatively regulates auxin-mediated root growth.

Root development is essential for plant survival. The lack of carotenoid biosynthesis in the phytoene desaturase 3 (pds3) mutant results in short primary roots (PRs) and reduced lateral root formation. In this study, we showed that short-term inhibition of PDS by fluridone suppresses PR growth in wild type, but to a lesser extent in auxin mutants of Arabidopsis (Arabidopsis thaliana). Such an inhibition of PDS activity increased endogenous indole-3-acetic acid levels, promoted auxin signaling, and partially complemented the PR growth of an auxin-deficient mutant, the YUCCA 3 5 7 8 9 quadruple mutant (yucQ). The exogenous application of retinaldehyde (retinal), an apocarotenoid derived from β-carotene, complemented the fluridone-induced suppression of root growth, as well as the short roots of the pds3 mutant. Retinal also partially complemented the auxin-induced suppression of root growth. These results suggest that retinal may play a role in regulating root growth by modulating endogenous auxin levels.