The nature of the interaction Azospirillum - Arabidopsis determine the molecular and morphological changes in root and p
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ORIGINAL ARTICLE
The nature of the interaction Azospirillum-Arabidopsis determine the molecular and morphological changes in root and plant growth promotion Manuel Méndez-Gómez 1 & Salvador Barrera-Ortiz 1 & Elda Castro-Mercado 1 & José López-Bucio 1 & Ernesto García-Pineda 1 Received: 9 May 2020 / Accepted: 31 August 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Plant growth promoting rhizobacteria influence host functional and adaptive traits via complex mechanisms that are just started to be clarified. Azospirillum brasilense acts as a probiotic bacterium, but detailed information about its molecular mechanisms of phytostimulation is scarce. Three interaction systems were established to analyze the impact of A. brasilense Sp245 on the phenotype of Arabidopsis seedlings, and underlying molecular responses were assessed under the following growth conditions: (1) direct contact of roots with the bacterium, (2) chemical communication via diffusible compounds produced by the bacterium, (3) signaling via volatiles. A. brasilense Sp245 improved shoot and root biomass and lateral root production in the three interaction systems assayed. Cell division, quiescent center, and differentiation protein reporters pCYCB1;1::GUS, WOX5::GFP, and pAtEXP7::GUS had a variable expression in roots depending of the nature of interaction. pCYCB1;1::GUS and WOX5::GFP increased with volatile compounds, whereas pAtEXP7::GUS expression was enhanced towards the root tip in plants with direct contact with the bacterium. The auxin reporter DR5::GUS was highly expressed with diffusible and volatile compounds, and accordingly, auxin signaling mutants pin3, slr1, arf7arf19, and tir1afb2afb3 showed differential phytostimulant responses when compared with the wild type. By contrast, ethylene signaling was not determinant to mediate root changes in response to the different interactions, as observed using the ethylene-related mutants etr1, ein2, and ein3. Our data highlight the diverse effects by which A. brasilense Sp245 improves plant growth and root architectural traits and define a critical role of auxin but not ethylene in mediating root response to bacterization. Keywords Azospirillum brasilense . Arabidopsis thaliana . Auxin . Ethylene . Plant growth . Root architecture
Introduction The plant microbiome supports growth, development, and adaptation, and many bacterial species are integral to host functioning via production of phytohormones, nitrogen fixation, Handling Editor: Ulrike Mathesius Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00709-020-01552-7) contains supplementary material, which is available to authorized users. * Ernesto García-Pineda [email protected] 1
Instituto de Investigaciones Químico Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Ciudad Universitaria, Edif. A1’, 58040 Morelia, Michoacan, Mexico
solubilization of phosphate, and induction of defense (Lugtenberg and Kamilova 2009; Vacheron et al. 2013). A very few bacterial sp
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