Fungal endophytes of Populus trichocarpa alter host phenotype, gene expression and rhizobiome composition.
Mortierella and Ilyonectria include common species of soil fungi which are frequently detected as root endophytes in many plants including Populus spp. However, the ecological roles of these and other endophytic fungi with respect to plant growth and function are still not well understood. The functional ecology of two key taxa from the Populus rhizobiome, Mortierella elongata PMI93 and Ilyonectria europaea PMI82, was studied by coupling forest soil bioassays with environmental metatranscriptomics. Using soil bioassay experiments amended with fungal inoculants, M. elongata was observed to promote the growth of Populus. This response was cultivar independent. In contrast, I. europaea had no visible effect on Populus growth. Metatranscriptomic studies reveal that these fungi impact rhizophytic and endophytic activities in Populus and induce shifts in soil and root microbial communities. Differential expression of core genes in P. trichocarpa roots was observed in response to both fungal species. Expression of Populus genes for lipid signaling and nutrient uptake were up-regulated and expression of genes associated with gibberellin signaling were altered in plants inoculated with M elongata, but not I. europaea. Up-regulation of genes for growth promotion, down-regulation of genes for several LRR-receptors/kinases, and alteration of expression of genes associated with plant defense responses (e.g., JA/ET/SA pathways) also suggest that M. elongata manipulates plant defenses while promoting plant growth.
Liao, H-L; Bonito, G; Rojas, JA; Hameed, K; Wu, S; Schadt, CW; Labbe, JL; Tuskan, G; Martin, FM; Grigoriev, IV; Vilgalys, R
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