β-Cyclocitral, a small molecule derived from β-carotene, was identified as a regulator of root stem cell behavior in Arabidopsis as well as in rice and tomato. β-Cyclocitral promotes root stem cell divisions to enhance root growth and branching. In rice, β-cyclocitral enhanced both root and shoot growth during salt stress, which has important implications for agriculture.
Natural compounds capable of increasing root depth and branching are desirable tools for enhancing stress tolerance in crops. We devised a sensitized screen to identify natural metabolites capable of regulating root traits in Arabidopsis. β-Cyclocitral, an endogenous root compound, was found to promote cell divisions in root meristems and stimulate lateral root branching. β-Cyclocitral rescued meristematic cell divisions in ccd1ccd4 biosynthesis mutants, and β-cyclocitral–driven root growth was found to be independent of auxin, brassinosteroid, and reactive oxygen species signaling pathways. β-Cyclocitral had a conserved effect on root growth in tomato and rice and generated significantly more compact crown root systems in rice. Moreover, β-cyclocitral treatment enhanced plant vigor in rice plants exposed to salt-contaminated soil. These results indicate that β-cyclocitral is a broadly effective root growth promoter in both monocots and eudicots and could be a valuable tool to enhance crop vigor under environmental stress.
Identification of β-cyclocitral, a root growth promoter in Arabidopsis. (A) The LR capacity of D15-treated plants, normalized to control plants. The IC50 is highlighted in red. (B) Seedlings after treatment with 30 μM D15 and 25 μM volatile β-cyclocitral (β-cyc). (Scale bar, 5 mm.) (C) LR capacity of plants treated with 30 μM D15 and 25 μM volatile β-cyclocitral. (D) Arabidopsis seedlings treated directly with 750 nM β-cyclocitral. (Scale bar, 5 mm.) (E) Quantification of LR capacity of seedlings treated with increasing concentrations of β-cyclocitral. (F) Quantification of primary root length in β-cyclocitral–treated plants. *P = 0.05, **P = 0.01, ***P = 0.001, and ****P = 0.0001.