The AFB1 auxin receptor controls the cytoplasmic auxin response pathway in Arabidopsis thaliana

• Published in: Molecular plant Vol. 16; no. 7; pp. 1120 - 1130
• Main Authors: Dubey, Shiv Mani, Han, Soeun, Stutzman, Nathan, Prigge, Michael J., Medvecká, Eva, Platre, Matthieu Pierre, Busch, Wolfgang, Fendrych, Matyáš, Estelle, Mark
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 03.07.2023
• Subjects: Arabidopsis; Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; auxin signaling; calcium; Cytosol - metabolism; F-Box Proteins - metabolism; Gene Expression Regulation, Plant; gravitropism; Indoleacetic Acids - metabolism; Indoleacetic Acids - pharmacology; lateral root; Plant Growth Regulators - metabolism; Plant Roots - metabolism; Receptors, Cell Surface - genetics; Receptors, Cell Surface - metabolism; calcium; gravitropism; Arabidopsis; lateral root; auxin signaling
• ISSN: 1674-2052; 1752-9867; 1752-9867
• DOI: 10.1016/j.molp.2023.06.008

The phytohormone auxin triggers root growth inhibition within seconds via a non-transcriptional pathway. Among members of the TIR1/AFB 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, is 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 by auxin. 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, whereas it regulates rapid changes in cell growth that contribute to root gravitropism. The phytohormone auxin triggers ultra-rapid responses in Arabidopsis roots, such as a cytoplasmic calcium spike, enabling rapid gravitropic response of roots. This study reveals that the auxin receptor AFB1 controls these early auxin responses from the cytoplasm of root cells and negatively regulates the emergence of lateral roots.