Differential inducible defense mechanisms against bacterial speck pathogen in Arabidopsis thaliana by plant-growth-promoting-fungus Penicillium sp. GP16-2 and its cell free filtrate

Abstract

Although a wealth of information is available regarding resistance induced by plant growthpromoting rhizobacteria (PGPR), not much is known about plant growth-promoting fungi (PGPF). Hence, the goal of the present research was to provide more information on this matter. In Arabidopsis thaliana L., root colonizing PGPF Penicillium sp. GP16-2 or its cell free filtrate (CF) elicited an induced systemic resistance (ISR) against infection by Pseudomonas syringae pv. tomato DC3000 (Pst), leading to a restriction of pathogen growth and disease development. We demonstrate that signal transduction leading to GP16-2-mediated ISR requires responsiveness to JA and ET in a NPR1-dependent manner, while CFmediated ISR shows dispensability of SA, JA, ET and NPR1-dependent signaling (at least individually). In addition, root colonization by GP16-2 is not associated with a direct effect on expression of known defenserelated genes, but potentiates the activation of JA/ETinducible ChitB, which only becomes apparent after infection by Pst. However, CF-mediated ISR was partly associated with the direct activation of marker genes responsive to both SA and JA/ET signaling pathways and partly associated with priming, leading to activation of JA-/ET-inducible ChitB and Hel genes. These suggest that CF may contain one or more elicitors that induce resistance by way where at least SA, JA and ET may play a role in defense signaling in Arabidopsis. Therefore, defense gene changes and underlying signaling pathways induced by Penicillium sp. GP16-2 root colonization and its CF application are not the same and only partially overlap.

Jasmonate signaling in plant interactions with resistance-inducing beneficial microbes

“…Likewise, ISR triggered by the PGPF Penicillium sp. GP16-2, Trichoderma harzianum T39 and P. indica was shown to be blocked in JAand ET-signaling mutants of Arabidopsis (Hossain et al, 2008;Korolev et al, 2008;Stein et al, 2008).…”

“…(Vinale et al, 2008), Penicillium sp. GP16-2 (Hossain et al, 2008), Pythium oligandrum (Hase et al, 2008), Piriformospora indica (Waller et al, 2005) and related Sebacinales spp. .…”

“…For instance, mutant Arabidopsis npr1 plants were shown to be blocked in their ability to express ISR upon colonization of the roots by the PGPR WCS417r , P. fluorescens CHAO (Iavicoli et al, 2003), P. fluorescens 89B61 (Ryu et al, 2003), Pseudomonas putida LSW17S (Ahn et al, 2007), Serratia marcescens 90-166 (Ryu et al, 2003) and B. pumilus SE34 (Ryu et al, 2003), and the PGPF Penicillium sp. GP16-2 (Hossain et al, 2008), P. indica (Stein et al, 2008) and T. asperellum T34 (Segarra et al, 2009). In SAR, NPR1 plays an important role as transcriptional co-activator of SA-responsive PR gene expression.…”

“…Likewise, colonization of Arabidopsis roots by the PGPF T. asperellum T34 (Segarra et al, 2009) or Penicillium sp. strain GP16-2 (Hossain et al, 2008) primed JA-responsive genes for enhanced expression upon pathogen attack. Analysis of the transcriptome of WCS417r-ISR revealed that the majority of the 81 Arabidopsis genes that were primed for enhanced expression upon infection by P. syringae were regulated by JA and/or ET (Verhagen et al, 2004; Fig.…”

Involvement of the Salicylic Acid Signaling Pathway in the Systemic Resistance Induced in Arabidopsis by Plant Growth-Promoting Fungus Fusarium equiseti GF19-1

“…In our study, GF19-1 caused growth promotion of Arabidopsis when it colonized the roots but failed to induce growth as a cell-free CF data not shown , suggesting that growth promotion is dependent on root colonization ability. Therefore, the mechanisms of growth promotion could involve the ability of the fungus to provide minerals to plants in a more available form rather than to its ability to produce growth-regulating substances 32 . This evidence suggests that colonization of roots to a certain extent by introduced beneficial microorganisms is necessary to exert beneficial effects on the plant 12,33 .…”