The Apocarotenoid β-Cyclocitric Acid Elicits Drought Tolerance in Plants

β-Cyclocitral (β-CC) is a volatile compound deriving from (1)O(2) oxidation of β-carotene in plant leaves. β-CC elicits a retrograde signal, modulating (1)O(2)-responsive genes and enhancing tolerance to photooxidative stress. Here, we show that β-CC is converted into water-soluble β-cyclocitric acid (β-CCA) in leaves. This metabolite is a signal that enhances plant tolerance to drought by a mechanism different from known responses such as stomatal closure, osmotic potential adjustment, and jasmonate signaling. This action of β-CCA is a conserved mechanism, being observed in various plant species, and it does not fully overlap with the β-CC-dependent signaling, indicating that β-CCA induces only a branch of β-CC signaling. Overexpressing SCARECROW-LIKE14 (SCL14, a regulator of xenobiotic detoxification) increased drought tolerance and potentiated the protective effect of β-CCA, showing the involvement of the SCL14-dependent detoxification in the phenomenon. β-CCA is a bioactive apocarotenoid that could potentially be used to protect crop plants against drought.