The phytohormone auxin triggers root growth inhibition within seconds via a non-transcriptional pathway. Among members of the TIR1/AFBs auxin receptor family, AFB1 has a primary role in this rapid response. However, the unique features that confer this specific function have not been identified. Here we show that the N-terminal region of AFB1, including the F-box domain and residues that contribute to auxin binding, are essential and sufficient for its specific role in the rapid response. Substitution of the N-terminal region of AFB1 with that of TIR1 disrupts its distinct cytoplasm-enriched localization and activity in rapid root growth inhibition. Importantly, the N-terminal region of AFB1 is indispensable for auxin-triggered calcium influx which is a prerequisite for rapid root growth inhibition. Furthermore, AFB1 negatively regulates lateral root formation and transcription of auxin-induced genes, suggesting that it plays an inhibitory role in canonical auxin signaling. These results suggest that AFB1 may buffer the transcriptional auxin response while it regulates rapid changes in cell growth that contribute to root gravitropism.

Department of Experimental Plant Biology Faculty of Sciences Charles University Prague Czech Republic

Plant Molecular and Cellular Biology Laboratory and Integrative Biology Laboratory Salk Institute for Biological Studies La Jolla United States

Section of Cell and Developmental Biology University of California San Diego La Jolla United States

Mol Plant. 2023 Jul 3;16(7):1120-1130. doi: 10.1016/j.molp.2023.06.008. PubMed

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