title: Host-related metabolic cues affect colonization strategies of a root endophyte.
abstract: The mechanisms underpinning broad compatibility in root symbiosis are largely unexplored. The generalist root endophyte Piriformospora indica establishes long-lasting interactions with morphologically and biochemically different hosts, stimulating their growth, alleviating salt stress, and inducing local and systemic resistance to pathogens. Cytological studies and global investigations of fungal transcriptional responses to colonization of barley and Arabidopsis at different symbiotic stages identified host-dependent colonization strategies and host-specifically induced effector candidates. Here, we show that in Arabidopsis, P. indica establishes and maintains biotrophic nutrition within living epidermal cells, whereas in barley the symbiont undergoes a nutritional switch to saprotrophy that is associated with the production of secondary thinner hyphae in dead cortex cells. Consistent with a diversified trophic behavior and with the occurrence of nitrogen deficiency at the onset of saprotrophy in barley, fungal genes encoding hydrolytic enzymes and nutrient transporters were highly induced in this host but not in Arabidopsis. Silencing of the high-affinity ammonium transporter PiAMT1 gene, whose transcripts are accumulating during nitrogen starvation and in barley, resulted in enhanced colonization of this host, whereas it had no effect on the colonization of Arabidopsis. Increased levels of free amino acids and reduced enzymatic activity for the cell-death marker VPE (vacuolar-processing enzyme) in colonized barley roots coincided with an extended biotrophic lifestyle of P. indica upon silencing of PiAMT1. This suggests that PiAmt1 functions as a nitrogen sensor mediating the signal that triggers the in planta activation of the saprotrophic program. Thus, host-related metabolic cues affect the expression of P. indica's alternative lifestyles.
authors.affiliation: Max-Planck-Institut für terrestrische Mikrobiologie, D-35043 Marburg, Germany.
authors.forename: Urs
authors.initials: U
authors.lastname: Lahrmann
authors.forename: Yi
authors.initials: Y
authors.lastname: Ding
authors.forename: Aline
authors.initials: A
authors.lastname: Banhara
authors.forename: Magnus
authors.initials: M
authors.lastname: Rath
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Hajirezaei
authors.forename: Stefanie
authors.initials: S
authors.lastname: Döhlemann
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
authors.forename: Martin
authors.initials: M
authors.lastname: Parniske
authors.forename: Alga
authors.initials: A
authors.lastname: Zuccaro
mesh_terms: D017360:Arabidopsis / Q000382:microbiology*; D001487:Basidiomycota / Q000378:metabolism / Q000502:physiology*; D027682:Cation Transport Proteins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D001467:Hordeum / Q000382:microbiology*; D046228:Microarray Analysis; D009747:Nutritional Physiological Phenomena / Q000502:physiology*; D018517:Plant Roots / Q000382:microbiology*; D034622:RNA Interference; D013045:Species Specificity; D013559:Symbiosis
chemical_list: D027682:Cation Transport Proteins
keywords: RCD; biotrophy; broad-host range; mutualism; root cortical cell death
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