The 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 (PR) and reduced lateral root (LR) formation. In this study, we show that short-term inhibition of PDS by fluridone suppressed PR growth in WT, but to a lesser extent in auxin mutants. Such an inhibition of PDS activity increased endogenous indole-3-acetic acid (IAA) levels, promoted auxin signaling, and partially complemented the PR growth of auxin deficient mutant, YUCCA 3 5 7 8 9 quadruple mutant (yucQ). The exogenous application of retinaldehyde (retinal), an apocarotenoid derived from {beta}-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. One-sentence summaryThe short-term inhibition of carotenoid biosynthesis mediates the production of {beta}-carotene-derived apocarotenoid retinal which negatively regulates auxin levels and signaling to control root growth.