β-cyclocitric acid: a new apocarotenoid eliciting 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 signaling, modulating 1 O 2 -responsive genes and enhancing tolerance to photooxidative stress. Here, we show that β-CC is largely converted into β-cyclocitric acid (β-CCA) in leaves and that this metabolite is a signal involved in stress tolerance. Treatment of Arabidopsis plants with β-CCA markedly enhanced plant tolerance to drought by a mechanism different from known responses such as stomatal closure, changes in osmotic potential and jasmonate signaling. Furthermore, we show that the response to β-CCA does not fully overlap with the β-CC-dependent signaling, indicating that β-CCA induces only a branch of the β-CC signaling pathway. In addition, the protective effect of β-CCA is a conserved mechanism, being observed in a variety of plant species. This study provides a new bioactive agent with promising agronomic applications for protecting plants against drought.