Intra‐species genetic variability drives carbon metabolism and symbiotic host interactions in the ectomycorrhizal fungus Pisolithus microcarpus

Abstract

Ectomycorrhizal (ECM) fungi are integral to boreal and temperate forest ecosystem functioning and nutrient cycling. ECM fungi, however, originate from diverse saprotrophic lineages and the impacts of genetic variation across species, and especially within a given ECM species, on function and interactions with the environment is not well understood. Here, we explore the extent of intra-species variation between four isolates of the ECM fungus Pisolithus microcarpus, in terms of gene regulation, carbon metabolism and growth, and interactions with a host, Eucalyptus grandis. We demonstrate that, while a core response to the host is maintained by all of the isolates tested, they have distinct patterns of gene expression and carbon metabolism, resulting in the differential expression of isolate-specific response pathways in the host plant. Together, these results highlight the importance of using a wider range of individuals within a species to understand the broader ecological roles of ECM fungi and their host interactions.

Novel Microdialysis Technique Reveals a Dramatic Shift in Metabolite Secretion during the Early Stages of the Interaction between the Ectomycorrhizal Fungus Pisolithus microcarpus and Its Host Eucalyptus grandis

“…Using microdialysis, we have captured metabolites secreted during the interaction of Eucalyptus grandis with the ECM fungus Pisolithus microcarpus over a time-course for the first 48-h of pre-symbiotic contact. With the availability of a sequenced genome for both organisms and the ability to form mycorrhizal root tips readily in vitro, E. grandis and P. microcarpus are important model species for the molecular study of ECM interactions [ 35 , 36 , 37 , 38 , 39 ]. Our results highlight not only the usefulness of microdialysis as a method for sampling metabolites but also the rapid and dramatic shift in the secreted metabolome of ECM fungi upon detection of a potential plant host.…”

Nitrogen fertilization differentially affects the symbiotic capacity of two co‐occurring ectomycorrhizal species

“…While this equates to 9% of significant DEGs being held in common to both N conditions, when we looked at the trend in the directionality of differential transcription in both conditions (e.g., genes showing increased transcript abundance in both high N and low N regardless of P-value), we found that >70% of these genes were expressed in a similar manner. As a number of past publications have used an in vitro system to investigate these ECM interactions at the transcriptomic level (Duplessis et al, 2005;Plett et al, 2015;Plett et al, 2021), we sought to understand how our results in a soil-based system compared to earlier studies performed in vitro. Using a previously published transcriptomic data from in vitro E. grandis seedlings colonized by the same isolate of P. microcarpus (Plett et al, 2021), we compared the expression patterns of those genes expressed in a similar manner in the soil conditions to in vitro expression (log2FC, colonized versus uninoculated control; Fig.…”

“…As a number of past publications have used an in vitro system to investigate these ECM interactions at the transcriptomic level (Duplessis et al, 2005;Plett et al, 2015;Plett et al, 2021), we sought to understand how our results in a soil-based system compared to earlier studies performed in vitro. Using a previously published transcriptomic data from in vitro E. grandis seedlings colonized by the same isolate of P. microcarpus (Plett et al, 2021), we compared the expression patterns of those genes expressed in a similar manner in the soil conditions to in vitro expression (log2FC, colonized versus uninoculated control; Fig. 3B).…”

The ectomycorrhizal fungus Pisolithus microcarpus encodes a microRNA involved in cross-kingdom gene silencing during symbiosis

“…In brief, following the method previously described in Wong et al. ( 45 ), E. grandis seeds were sterilized, germinated, and placed into symbiotic interaction with four isolates of the model ECM fungal species P. microcarpus [isolates SI9, SI14, R4, and R10; ( 46 )] to identify miRNAs. A time course of colonization between P. microcarpus isolates SI14 and SI9 and E. grandis was used to profile the expression of identified miRNAs over the course of colonization (i.e., 24 h, 48 h, and 2 wk).…”

“…On the 14th day of colonization (seventh day of sRNA treatment), ECM colonization rate was scored, as were the number of senesced mycorrhizal root tips. Hartig net formation was analyzed as previously described ( 46 ). Samples were also collected, and RNA transcript quantitation by qPCR (Primers found in Dataset S7 ) was used to verify that Pmic_miR-8 was differentially regulated as expected using a stem loop qRT-PCR approach, as described previously ( 51 ).…”