Sustained exposure to abscisic acid enhances the colonization potential of the mutualist fungus Piriformospora indica on Arabidopsis thaliana roots

Abstract

SummaryRoot colonization by the beneficial fungus Piriformospora indica is controlled by plant innate immunity, but factors that channel this interaction into a mutualistic relationship are not known. We have explored the impact of abscisic acid (ABA) and osmotic stress on the P. indica interaction with Arabidopsis thaliana.The activation of plant innate immunity in roots was determined by measuring the concentration of the phytoalexin camalexin and expression of transcription factors regulating the biosynthesis of tryptophan-related defence metabolites. Furthermore, the impact of the fungus on the content of ABA, salicylic acid, jasmonic acid (JA) and JA-related metabolites was examined.We demonstrated that treatment with exogenous ABA or the ABA analogue pyrabactin increased fungal colonization efficiency without impairment of plant fitness. Concomitantly, ABA-deficient mutants of A. thaliana (aba1-6 and aba2-1) were less colonized, while plants exposed to moderate stress were more colonized than corresponding controls. Sustained exposure to ABA attenuated expression of transcription factors MYB51, MYB122 and WRKY33 in roots upon P. indica challenge or chitin treatment, and prevented an increase in camalexin content.The results indicate that ABA can strengthen the interaction with P. indica as a consequence of its impact on plant innate immunity. Consequently, ABA will be relevant for the establishment and outcome of the symbiosis under stress conditions.

Piriformospora indica Stimulates Root Metabolism of Arabidopsis thaliana

“…Hormonal regulation has been described to accompany the colonization of P. indica on A. thaliana roots [ 22 , 23 , 24 , 32 , 33 , 34 , 35 ]. An enrichment analysis ( Table 1 and Supplementary Table S1 ) of the upregulated root transcripts 14 dpi as published in Lahrmann et al [ 24 ] revealed an overrepresentation of genes involved in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway “Biosynthesis of plant hormones” (ath01070).…”

Transcriptional responses of soybean roots to colonization with the root endophytic fungus Piriformospora indica reveals altered phenylpropanoid and secondary metabolism

“…The phytohormone ABA plays a crucial role in adaptive responses to environmental stresses, as higher ABA expression in response to drought and high salinity induces massive changes in gene expression resulting in stomatal closure 31 , 121 . An overexpression mutant of a homolog of an ABA responsive gene that was upregulated in our data (Supplementary Tables S5 and S7 ), ATbetaFruct4, showed higher levels in leaf stomatal guard cells and led to increased drought tolerance in Arabidopsis 80 .…”

“…The production and signaling of the phytohormones ethylene, jasmonic acid (JA), gibberellic acid (GA), salicylic acid (SA) and abscisic acid (ABA) have all been shown to be impacted by P . indica 29 – 31 . Changes in levels of these hormones likely mediate abiotic stress responses 13 , 32 as well as regulate biotic responses such as induced and systemic plant defense responses, microbe-associated molecular patterns (MAMP) triggered immunity 6 , 29 , 33 , and autoregulation of mutualistic symbionts 34 – 36 .…”

Alternaria Brassicae Induces Systemic Jasmonate Responses in Arabidopsis Which Travel to Neighboring Plants via a Piriformsopora Indica Hyphal Network and Activate Abscisic Acid Responses

“…Connecting plants by a P. indica hyphal network resulted in elevated ABA levels and expression of ABA-responsive genes in non-infested plants (Figure 6 , Table 1 ). Also Peskan-Berghöfer et al ( 2015 ) showed that elevated ABA levels triggered by osmotic stress promoted P. indica colonization of the roots, without impairing plant fitness. Furthermore, sustained exposure to ABA muted defense response in roots and thereby made them more accessible for the mutualist.…”