Effect of fungal-isolate aggressivity on the biosynthesis of symbiosis-related polypeptides in differentiating eucalypt ectomycorrhizas

Changes in protein biosynthesis were examined during the early stages of differentiation of Eucalyptus grandis-Pisolithus tinctorius ectomycorrhizas by two-dimensional polyacrylamide gel electrophoresis of ³⁵S-labelled proteins. Three distinct isolates of P. tinctorius Coker & Couch were chosen based on the rate of ectomycorrhizal formation (i.e. infectivity) with E. grandis W. Hill ex Maiden. The isolate H506 was not able to induce mycorrhiza, isolate 441 showed moderate infectivity and isolate H2144 exhibited a very high infectivity. Mycorrhiza were produced in vitro in a system where seeds were germinated in the presence of fungal mycelium and exudates. The non-mycorrhizal isolate caused no changes in root protein biosynthesis as analyzed by two-dimensional polyacrylamide gel electrophoresis, whereas drastic alterations in protein biosynthesis were observed from initial contact with the aggressive mycobionts. During mycorrhizal development, there was a marked inhibition of plant polypeptides synthesis, enhanced accumulation of some fungal polypeptides and the emergence of symbiosis-specific polypeptides, the so-called ectomycorrhizins. The major changes were observed in a group of fungal acidic polypeptides (apparent molecular weight 28–32 kDa) including the ectomycorrhizin E₃₂. These polypeptides first appeared at contact and their synthesis increased during mycorrhizal formation, suggesting a role in mycorrhizal development, most likely as structural proteins. Up-regulation of the synthesis of fungal symbiosis-related polypeptides was tightly correlated to the infectivity of the strain.Abbreviations FW fresh weight - MW molecular weight - pI isoelectric point - SR-polypeptides symbiosis-related polypeptides This work was supported by a research grant from the Eureka-Eurosilva programme (Changes in Gene Expression during Ectomycorrhiza Differentiation and Function) to F.M. and a Murdoch University Special Research Grant to B.D; T.B. was a recipient of a Doctoral Fellowship from the INRA and an Australian Postgraduate Scholarship. We would like to thank Dr Denis Tagu and Dulcinéia de Carvalho (Institut National de la Recherche Agronomique, Nancy, France) for helpful discussions.