Effect of poplar genotypes on mycorrhizal infection and secreted enzyme activities in mycorrhizal and non-mycorrhizal roots

Abstract

The impact of ectomycorrhiza formation on the secretion of exoenzymes by the host plant and the symbiont is unknown. Thirty-eight F1 individuals from an interspecific Populus deltoides (Bartr.)×Populus trichocarpa (Torr. & A. Gray) controlled cross were inoculated with the ectomycorrhizal fungus Laccaria bicolor. The colonization of poplar roots by L. bicolor dramatically modified their ability to secrete enzymes involved in organic matter breakdown or organic phosphorus mobilization, such as N-acetylglucosaminidase, β-glucuronidase, cellobiohydrolase, β-glucosidase, β-xylosidase, laccase, and acid phosphatase. The expression of genes coding for laccase, N-acetylglucosaminidase, and acid phosphatase was studied in mycorrhizal and non-mycorrhizal root tips. Depending on the genes, their expression was regulated upon symbiosis development. Moreover, it appears that poplar laccases or phosphatases contribute poorly to ectomycorrhiza metabolic activity. Enzymes secreted by poplar roots were added to or substituted by enzymes secreted by L. bicolor. The enzymatic activities expressed in mycorrhizal roots differed significantly between the two parents, while it did not differ in non-mycorrhizal roots. Significant differences were found between poplar genotypes for all enzymatic activities measured on ectomycorrhizas except for laccases activity. In contrast, no significant differences were found between poplar genotypes for enzymatic activities of non-mycorrhizal root tips except for acid phosphatase activity. The level of enzymes secreted by the ectomycorrhizal root tips is under the genetic control of the host. Moreover, poplar heterosis was expressed through the enzymatic activities of the fungal partner.

Structure and Expression Profile of the Phosphate Pht1 Transporter Gene Family in Mycorrhizal Populus trichocarpa

“…Our results also suggested that the mycorrhizal Pi uptake pathway in poplar is controlled to a large part by the host plant through the differential activation of symbiosis-specific Pi transporter genes. This mechanism is in agreement with the observation that the pattern of secretory enzyme activities of EMs is largely determined by the poplar genotype (Courty et al, 2011).…”

Certainties and uncertainties about the life cycle of the Périgord black truffle (Tuber melanosporum Vittad.)

“…Unknown factors, which remained to be discovered, are necessary for ascocarp initiation. Courty et al (2010) demonstrated that poplar clones differentially control gene expression of their fungal associates. Tuber fructification could also be under the genetic control of the host.…”

Secreted enzymatic activities of ectomycorrhizal fungi as a case study of functional diversity and functional redundancy

“…We believe that facilitation is occurring because the different ECMf species may contribute differently to mobilize different resources by secreting substrate-specific enzymes, not detectable in the microplate assay used here. Moreover, at a species level, functional diversity is also determined by the fungal and the host genetic diversity (Courty et al 2011).…”

“…The structure and the diversity of ECM communities has been extensively studied across a wide range of forest types (e.g., Courty et al 2008;Tedersoo et al 2010) as well as its response to seasons, tree phenology, host genotype, soil chemistry, or environmental disturbances (e.g., Parrent et al 2006;Courty et al 2007Courty et al , 2010bCourty et al , 2011Dickie et al 2009;Rineau and Garbaye 2009a), but the structure-function relation in these communities has been uncompletely addressed (Leake et al 2002). Studies of ecological preferences and resilience of ECMf species according to disturbances are rare (Elmqvist et al 2003;Folke et al 2004).…”