The AUX1-AFB1-CNGC14 module establishes a longitudinal root surface pH profile
Abstract
Plant roots navigate in the soil environment following the gravity vector. Cell divisions in the meristem and rapid cell growth in the elongation zone propel the root tips through the soil. Actively elongating cells acidify their apoplast to enable cell wall extension by the activity of plasma membrane AHA H+-ATPases. The phytohormone auxin, central regulator of gravitropic response and root development, inhibits root cell growth, likely by rising the pH of the apoplast. However, the role of auxin in the regulation of the apoplastic pH gradient along the root tip is unclear. Here we show, by using an improved method for visualization and quantification of root surface pH, that the Arabidopsis thaliana root surface pH shows distinct acidic and alkaline zones, which are not primarily determined by the activity of AHA H+-ATPases. Instead, the distinct domain of alkaline pH in the root transition zone is controlled by a rapid auxin response module, consisting of the AUX1 auxin influx carrier, the AFB1 auxin co-receptor and the CNCG14 calcium channel. We demonstrate that the rapid auxin response pathway is required for an efficient navigation of the root tip.
Data availability
All the data used for the the manuscript are available at Zenodo.The statistics used and p-values are available as supplementary file.
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The AUX1-AFB1-CNGC14 module establishes a longitudinal root surface pH profile main figuresZenodo, doi: 10.5281/zenodo.8138861.
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The AUX1-AFB1-CNGC14 module establishes a longitudinal root surface pH profile supplementary figuresZenodo, doi: 10.5281/zenodo.8140893.
Article and author information
Author details
Funding
European Research Council (803048)
- Nelson BC Serre
- Daša Wernerová
- Pruthvi Vittal
- Shiv Mani Dubey
- Eva Medvecká
- Matyáš Fendrych
Deutsche Forschungsgemeinschaft (GR4559)
- Guido Grossmann
Deutsche Forschungsgemeinschaft (CRC1208)
- Guido Grossmann
EPLAS-EXC-2048/1 (390686111)
- Guido Grossmann
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Yoselin Benitez-Alfonso, University of Leeds, United Kingdom
Version history
- Preprint posted: November 24, 2022 (view preprint)
- Received: November 26, 2022
- Accepted: July 10, 2023
- Accepted Manuscript published: July 14, 2023 (version 1)
- Version of Record published: August 10, 2023 (version 2)
Copyright
© 2023, Serre et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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- Biochemistry and Chemical Biology
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Metabolism and biological functions of the nitrogen-rich compound guanidine have long been neglected. The discovery of four classes of guanidine-sensing riboswitches and two pathways for guanidine degradation in bacteria hint at widespread sources of unconjugated guanidine in nature. So far, only three enzymes from a narrow range of bacteria and fungi have been shown to produce guanidine, with the ethylene-forming enzyme (EFE) as the most prominent example. Here, we show that a related class of Fe2+- and 2-oxoglutarate-dependent dioxygenases (2-ODD-C23) highly conserved among plants and algae catalyze the hydroxylation of homoarginine at the C6-position. Spontaneous decay of 6-hydroxyhomoarginine yields guanidine and 2-aminoadipate-6-semialdehyde. The latter can be reduced to pipecolate by pyrroline-5-carboxylate reductase but more likely is oxidized to aminoadipate by aldehyde dehydrogenase ALDH7B in vivo. Arabidopsis has three 2-ODD-C23 isoforms, among which Din11 is unusual because it also accepted arginine as substrate, which was not the case for the other 2-ODD-C23 isoforms from Arabidopsis or other plants. In contrast to EFE, none of the three Arabidopsis enzymes produced ethylene. Guanidine contents were typically between 10 and 20 nmol*(g fresh weight)-1 in Arabidopsis but increased to 100 or 300 nmol*(g fresh weight)-1 after homoarginine feeding or treatment with Din11-inducing methyljasmonate, respectively. In 2-ODD-C23 triple mutants, the guanidine content was strongly reduced, whereas it increased in overexpression plants. We discuss the implications of the finding of widespread guanidine-producing enzymes in photosynthetic eukaryotes as a so far underestimated branch of the bio-geochemical nitrogen cycle and propose possible functions of natural guanidine production.
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- Plant Biology
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