Multilayered Organization of Jasmonate Signalling in the Regulation of Root Growth

RESEARCH ARTICLE Multilayered Organization of Jasmonate Signalling in the Regulation of Root Growth Debora Gasperini1, Aurore Chételat1, Ivan F. Acosta1¤, Jonas Goossens2,3, Laurens Pauwels2,3, Alain Goossens2,3, René Dreos4, Esteban Alfonso1, Edward E. Farmer1* 1 Department of Plant Molecular Biology, University of Lausanne, Lausanne, Switzerland, 2 Department of Plant Systems Biology, Flanders Institute for Biotechnology (VIB), Gent, Belgium, 3 Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium, 4 Swiss Institute of Bioinformatics, Lausanne, Switzerland ¤ Current address: Max Planck Institute for Plant Breeding Research, Cologne, Germany * Abstract OPEN ACCESS Citation: Gasperini D, Chételat A, Acosta IF, Goossens J, Pauwels L, Goossens A, et al. (2015) Multilayered Organization of Jasmonate Signalling in the Regulation of Root Growth. PLoS Genet 11(6): e1005300. doi:10.1371/journal.pgen.1005300 Editor: Hao Yu, National University of Singapore and Temasek Life Sciences Laboratory, SINGAPORE Received: February 12, 2015 Accepted: May 27, 2015 Published: June 12, 2015 Copyright: © 2015 Gasperini et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files with the exception of raw gene expression data which can be downloaded from GEO, accession no. GSE65840. Funding: This work was supported by Swiss National Science Foundation (http://www.snf.ch/en/ Pages/default.aspx) Grants 31003A-138235 and 31003A-155960/1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Physical damage can strongly affect plant growth, reducing the biomass of developing organs situated at a distance from wounds. These effects, previously studied in leaves, require the activation of jasmonate (JA) signalling. Using a novel assay involving repetitive cotyledon wounding in Arabidopsis seedlings, we uncovered a function of JA in suppressing cell division and elongation in roots. Regulatory JA signalling components were then manipulated to delineate their relative impacts on root growth. The new transcription factor mutant myc2-322B was isolated. In vitro transcription assays and whole-plant approaches revealed that myc2-322B is a dosage-dependent gain-of-function mutant that can amplify JA growth responses. Moreover, myc2-322B displayed extreme hypersensitivity to JA that totally suppressed root elongation. The mutation weakly reduced root growth in undamaged plants but, when the upstream negative regulator NINJA was genetically removed, myc2322B powerfully repressed root growth through its effects on cell division and cell elongation. Furthermore, in a JA-deficient mutant background, ninja1 myc2-322B still repressed root elongation, indicating that it is possible to generate JA-responses in the absence of JA. We show that NINJA forms a broadly expressed regulatory layer that is required to inhibit JA signalling in the apex of roots grown under basal conditions. By contrast, MYC2, MYC3 and MYC4 displayed cell layer-specific localisations and MYC3 and MYC4 were expressed in mutually exclusive regions. In nature, growing roots are likely subjected to constant mechanical stress during soil penetration that could lead to JA production and subsequent detrimental effects on growth. Our data reveal how distinct negative regulatory layers, including both NINJA-dependent and -independent mechanisms, restrain JA responses to allow normal root growth. Mechanistic insights from this work underline the importance of mapping JA signalling components to specific cell types in order to understand and potentially engineer the growth reduction that follows physical damage. PLOS Genetics | DOI:10.1371/journal.pgen.1005300 June 12, 2015 1 / 27 Repressed Root Growth in a Novel MYC2 Allele Competing Interests: The authors have declared that no competing interests exist. Author Summary The study of plant development is generally carried out in the absence of physical injury. However, damage to plant organs through biotic and abiotic insult is common in nature. Under these conditions the jasmonate pathway that has a low activity in unstressed vegetative tissues imposes its activity on cell division and elongation. Such jasmonate-dependent growth restriction can strongly impact plant productivity. Taking roots as a model, we show that it is possible to manipulate regulatory layers in jasmonate signalling such that cell division and cell elongation can be constrained differently. This approach may lead to future strategies to alter organ growth. Moreover, during this study we identified a novel mutant in a key regulator of the jasmonate pathway. This mutant generated a positive regulator of jasmonate signalling that was so active that we were able to show that hormone synthesis can be completely uncoupled from hormone responses, suggesting ways to modify traits of potential agronomic importance. Introduction The development, architecture and mass of nascent plant organs are plastic and can be strongly influenced by injury to pre-existing tissues. Wounding reduces plant biomass and damage to young tissues can strongly reduce growth rates, e.g. [1]. In the case of above ground tissues, most of the growth restriction that occurs subsequently to physical damage depends on the activation of the jasmonate (JA) pathway [2–4], which has a pivotal role in controlling herbivoreinducible gene expression and coordinating resource allocation between defence and growth [5, 6]. In contrast to the observation of JA-mediated growth restriction in leaves, root growth responses following damage to aerial organs are so far, not clearly understood. Additionally, there is relatively little knowledge of the cellular organization of JA signalling components in roots. What has emerged to date, however, is that the same basic JA signalling components operate in shoots and roots, although the genetic architecture of the JA pathway appears to be simpler in roots [7]. JA signalling, whether for defence or organ growth restriction, requires the production and perception of low molecular mass lipidic regulators of the JA family, including the biologically active form jasmonoyl-L-isoleucine (JA-Ile) [8, 9]. The transcriptional changes resulting from JA-Ile perception enable plants to modulate the allocation of resources in defense at the expense of growth [3]. In the absence of JA-Ile, JASMONATE ZIM-DOMAIN (JAZ) proteins bind and repress JA-dependent transcription factors (TFs) by recruiting the general co-repressors TOPLESS (TPL) and TPL-Related (TPR) proteins through an interaction with the adaptor protein Novel Interactor of JAZ (NINJA) [10], or direct (...truncated)