β-cyclocitric acid: a new apocarotenoid eliciting drought tolerance in plants
{beta}-Cyclocitral ({beta}-CC) is a volatile compound deriving from 1O2 oxidation of {beta}-carotene in plant leaves. {beta}-CC elicits a retrograde signaling, modulating 1O2-responsive genes and enhancing tolerance to photooxidative stress. Here, we show that {beta}-CC is largely converted into {beta}-cyclocitric acid ({beta}-CCA) in leaves and that this metabolite is a signal involved in stress tolerance. Treatment of Arabidopsis plants with {beta}-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 {beta}-CCA does not fully overlap with the {beta}-CC-dependent signaling, indicating that {beta}-CCA induces only a branch of the {beta}-CC signaling pathway. In addition, the protective effect of {beta}-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.