A Complex Molecular Interplay of Auxin and Ethylene Signaling Pathways Is Involved in Arabidopsis Growth Promotion by Burkholderia phytofirmans PsJN

Abstract

Modulation of phytohormones homeostasis is one of the proposed mechanisms to explain plant growth promotion induced by beneficial rhizobacteria (PGPR). However, there is still limited knowledge about the molecular signals and pathways underlying these beneficial interactions. Even less is known concerning the interplay between phytohormones in plants inoculated with PGPR. Auxin and ethylene are crucial hormones in the control of plant growth and development, and recent studies report an important and complex crosstalk between them in the regulation of different plant developmental processes. The objective of this work was to study the role of both hormones in the growth promotion of Arabidopsis thaliana plants induced by the wellknown PGPR Burkholderia phytofirmans PsJN. For this, the spatiotemporal expression patterns of several genes related to auxin biosynthesis, perception and response and ethylene biosynthesis were studied, finding that most of these genes showed specific transcriptional regulations after inoculation in roots and shoots. PsJN-growth promotion was not observed in Arabidopsis mutants with an impaired ethylene (ein2-1) or auxin (axr1-5) signaling. Even, PsJN did not promote growth in an ethylene overproducer (eto2), indicating that a fine regulation of both hormones signaling and homeostasis is necessary to induce growth of the aerial and root tissues. Auxin polar transport is also involved in growth promotion, since PsJN did not promote primary root growth in the pin2 mutant or under chemical inhibition of transport in wild type plants. Finally, a key role for ethylene biosynthesis was found in the PsJN-mediated increase in root hair number. These results not only give new insights of PGPR regulation of plant growth but also are also useful to understand key aspects of Arabidopsis growth control.

A New Approach to Modify Plant Microbiomes and Traits by Introducing Beneficial Bacteria at Flowering into Progeny Seeds

“…Recently, increasing efforts have been made to understand the molecular mechanisms of the interaction between strain PsJN and host plants. The observed positive effect of strain PsJN on plants is at least partly based on altered gene expression in the host plant (Lara-Chavez et al, 2015; Pinedo et al, 2015; Poupin et al, 2016) in the presence of PsJN. The bacterium itself is also active inside plant.…”

Anatomical and Biochemical Changes Induced by Gluconacetobacter diazotrophicus Stand Up for Arabidopsis thaliana Seedlings From Ralstonia solanacearum Infection

“…The ISR is characterized for being activated after the interaction between beneficial microorganisms and their host plants; this induction is signaled by the ethylene (ET) and jasmonic acid (JA) or salicylic acid (SA) pathways or a combination of both signaling pathways. When the induced resistance is demonstrated to be SA dependent, is referred to as systemic acquired resistance (SAR) (Pieterse et al, 2014). Several studies showed that relatively slight changes occurred in the transcriptome in systemic tissues upon a colonization of the roots by a beneficial microorganism, especially when compared with the massive transcriptional reprogramming that occurs during the attack of pathogens (Verhagen et al, 2004).…”

“…Several studies showed that relatively slight changes occurred in the transcriptome in systemic tissues upon a colonization of the roots by a beneficial microorganism, especially when compared with the massive transcriptional reprogramming that occurs during the attack of pathogens (Verhagen et al, 2004). Because the defense mechanisms remain dormant after interaction with beneficial microorganisms, it is sometimes difficult to recognize them in plants that have not been challenged by an interaction with a pathogen; therefore the combination in the interaction plant-beneficial microorganism-pathogen allows studying and visualizing the ISR changes easily (Pieterse et al, 2014).…”

Promoção de crescimento vegetal por <i>Bacillus</i> sp. RZ2MS9: dos genes ao campo

“…AvH-4, P. aeruginosa AS-17 (Ali 2015) e Burkholderia phytofirmans PsJN (Poupin et al 2016) na promoção de crescimento vegetal e modificação de arquitetura radicular.…”

“…Estudos mais recentes utilizando também mutantes de Arabidopsis thaliana insensíveis a auxinas e etileno demonstraram que a indução de crescimento vegetal por B. subtilis TpP-1, Pseudomonas sp. AvH-4, P. aeruginosa AS-17 (Ali 2015) e Burkholderia phytofirmans PsJN (Poupin et al 2016) está associada à sinalização bacteriana desses hormônios.…”