The biocontrol endophytic bacterium Pseudomonas fluorescens PICF7 induces systemic defense responses in aerial tissues upon colonization of olive roots

Abstract

Pseudomonas fluorescens PICF7, a native olive root endophyte and effective biocontrol agent (BCA) against Verticillium wilt of olive, is able to trigger a broad range of defense responses in root tissues of this woody plant. In order to elucidate whether strain PICF7 also induces systemic defense responses in above-ground organs, aerial tissues of olive plants grown under non-gnotobiotic conditions were collected at different time points after root bacterization with this endophytic BCA. A suppression subtractive hybridization (SSH) cDNA library, enriched in up-regulated genes, was generated. This strategy enabled the identification of 376 ESTs (99 contigs and 277 singlets), many of them related to response to different stresses. Five ESTs, involved in defense responses, were selected to carry out time-course quantitative real-time PCR (qRT-PCR) experiments aiming to: (1) validate the induction of these genes, and (2) shed light on their expression pattern along time (from 1 to 15 days). Induction of olive genes potentially coding for lipoxygenase 2, catalase, 1-aminocyclopropane-1-carboxylate oxidase, and phenylananine ammonia-lyase was thus confirmed at some time points. Computational analysis also revealed that different transcription factors were up-regulated in olive aerial tissues (i.e., JERF, bHLH, WRKY), as previously reported for roots. Results confirmed that root colonization by this endophytic bacterium does not only trigger defense responses in this organ but also mounts a wide array of systemic defense responses in distant tissues (stems, leaves). This sheds light on how olive plants respond to the “non-hostile” colonization by a bacterial endophyte and how induced defense response can contribute to the biocontrol activity of strain PICF7.

The Influence of Land Use Intensity on the Plant-Associated Microbiome of Dactylis glomerata L.

“…Pseudomonadaceae are reported to exhibit a wide range of plant-beneficial properties and plant growth-promoting traits. These include phosphate solubilization, nitrogen fixation, synthesis of cytokinins as well as of the phytohormones indole-3-acetic acid (IAA) and gibberellins (Cabanas et al, 2014; Vacheron et al, 2016). The latter was reported to affect seed formation and ripening in grasses (Stoddart, 1965; Kim et al, 2016), emphasizing the importance of Pseudomonadaceae in our study.…”

Endophytic colonization and biocontrol performance of Pseudomonas fluorescens PICF7 in olive (Olea europaea L.) are determined neither by pyoverdine production nor swimming motility

“…One of the best BCA of VWO so far studied is the olive root endophyte P. fluorescens PICF7 (Mercado‐Blanco et al ., ; Prieto et al ., 2009; 2011). Strain PICF7 is able to trigger a broad range of defence responses in both root (Schilirò et al ., ) and aerial (Gómez‐Lama Cabanás et al ., ) tissues, pointing to a scenario in which VWO biocontrol by PICF7 could be mediated by induced resistance mechanism(s) (Pieterse et al ., ). We have recently shown, however, that the presence of PICF7 cells in root tissues does not suppress olive knot disease in stems caused by Pseudomonas savastanoi pv.…”

Desirable Traits of a Good Biocontrol Agent against Verticillium Wilt

“…FP12 (Papasotiriou et al, 2013). The endophytic BCA P. fluorescens PICF7 has been shown to activate an array of defense pathways in the roots and aerial tissues of olive upon colonization of the roots (Schilirò et al, 2012; Gómez-Lama Cabanás et al, 2014). Recently, Gómez-Lama Cabanás et al (2017) demonstrated that the expression of defense-related genes differed depending on whether or not V. dahliae and P. fluorescens PICF7 colonized the same sectors of the roots of olive plants.…”