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Proc Natl Acad Sci U S A. 2018 Jun 26;115(26):6864-6869. doi: 10.1073/pnas.1806565115. Epub 2018 Jun 13.

Auxin methylation is required for differential growth in Arabidopsis.

Author information

1
Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
2
Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria.
3
Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid-Instituto Nacional de Investigación y Tecnología Agraria y Alimentación, 28223 Pozuelo de Alarcón, Spain.
4
Institute of Synthetic Biology and Cluster of Excellence in Plant Sciences, University of Düsseldorf, 40225 Düsseldorf, Germany.
5
Spemann Graduate School of Biology and Medicine, University of Freiburg, 79085 Freiburg, Germany.
6
Department of Cell Biology and Biochemistry, Regensburg University, 93053 Regensburg, Germany.
7
Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain; mblazquez@ibmcp.upv.es.

Abstract

Asymmetric auxin distribution is instrumental for the differential growth that causes organ bending on tropic stimuli and curvatures during plant development. Local differences in auxin concentrations are achieved mainly by polarized cellular distribution of PIN auxin transporters, but whether other mechanisms involving auxin homeostasis are also relevant for the formation of auxin gradients is not clear. Here we show that auxin methylation is required for asymmetric auxin distribution across the hypocotyl, particularly during its response to gravity. We found that loss-of-function mutants in Arabidopsis IAA CARBOXYL METHYLTRANSFERASE1 (IAMT1) prematurely unfold the apical hook, and that their hypocotyls are impaired in gravitropic reorientation. This defect is linked to an auxin-dependent increase in PIN gene expression, leading to an increased polar auxin transport and lack of asymmetric distribution of PIN3 in the iamt1 mutant. Gravitropic reorientation in the iamt1 mutant could be restored with either endodermis-specific expression of IAMT1 or partial inhibition of polar auxin transport, which also results in normal PIN gene expression levels. We propose that IAA methylation is necessary in gravity-sensing cells to restrict polar auxin transport within the range of auxin levels that allow for differential responses.

KEYWORDS:

auxin metabolism; gravitropism; homeostasis; hormone regulation

PMID:
29899148
PMCID:
PMC6042151
DOI:
10.1073/pnas.1806565115
[Indexed for MEDLINE]
Free PMC Article

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