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Authors: Linlin Qi, Mateusz Kwiatkowski, Huihuang Chen, Lukas Hoermayer, Scott Sinclair, Minxia Zou, Charo I. del Genio, Martin F. Kubeš, Richard Napier, Krzysztof Jaworski and Jiří Friml.
Nature (2022)
One-sentence summary: Adenylate cyclase activity in TIR1/AFB, the canonical auxin receptor, has an essential role in auxin-mediated root growth inhibition in land plants.
Abstract: "The phytohormone auxin is the major coordinative signal in plant development1, mediating transcriptional reprogramming by a well-established canonical signalling pathway. TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFB) auxin receptors are F-box subunits of ubiquitin ligase complexes. In response to auxin, they associate with Aux/IAA transcriptional repressors and target them for degradation via ubiquitination2,3. Here we identify adenylate cyclase (AC) activity as an additional function of TIR1/AFB receptors across land plants. Auxin, together with Aux/IAAs, stimulates cAMP production. Three separate mutations in the AC motif of the TIR1 C-terminal region, all of which abolish the AC activity, each render TIR1 ineffective in mediating gravitropism and sustained auxin-induced root growth inhibition, and also affect auxin-induced transcriptional regulation. These results highlight the importance of TIR1/AFB AC activity in canonical auxin signalling. They also identify a unique phytohormone receptor cassette combining F-box and AC motifs, and the role of cAMP as a second messenger in plants."
