Fluorescent Auxin Analogs Report Two Auxin Binding Sites with Different Subcellular Distribution and Affinities: A Cue for Non-Transcriptional Auxin Signaling

• Published in: International journal of molecular sciences 2022-08, Vol.23 (15), p.8593
• Main Authors: Huang, Xiang, Maisch, Jan, Hayashi, Ken-Ichiro, Nick, Peter
• Format: Article
• Language: English
• Subjects: 2,4-D; Acetic acid; Acids; Affinity; Analogs; auxin; Auxins; binding site; Binding sites; Cell division; Dichlorophenoxyacetic acid; Endoplasmic reticulum; Fluorescent indicators; Gene expression; indole acetic acid; Indoleacetic acid; Kinases; Localization; Naphthaleneacetic acid; NBD auxins; Plant growth; Proteins; Sensors; tonoplast
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms23158593

The complexity of auxin signaling is partially due to multiple auxin receptors that trigger differential signaling. To obtain insight into the subcellular localization of auxin-binding sites, we used fluorescent auxin analogs that can undergo transport but do not deploy auxin signaling. Using fluorescent probes for different subcellular compartments, we can show that the fluorescent analog of 1-naphthaleneacetic acid (NAA) associates with the endoplasmic reticulum (ER) and tonoplast, while the fluorescent analog of indole acetic acid (IAA) binds to the ER. The binding of the fluorescent NAA analog to the ER can be outcompeted by unlabeled NAA, which allows us to estimate the affinity of NAA for this binding site to be around 1 μM. The non-transportable auxin 2,4-dichlorophenoxyacetic acid (2,4-D) interferes with the binding site for the fluorescent NAA analog at the tonoplast but not with the binding site for the fluorescent IAA analog at the ER. We integrate these data into a working model, where the tonoplast hosts a binding site with a high affinity for 2,4-D, while the ER hosts a binding site with high affinity for NAA. Thus, the differential subcellular localization of binding sites reflects the differential signaling in response to these artificial auxins.