Regulation of gene expression in ectomycorrhizas

SUMMARY In an effort to investigate the presence of any ‘symbiosis‐specific’ genes that are expressed specifically during the development of ectomycorrhizas, the polypeptide content of Eucalyptus‐Pisolithus mycorrhizas, uninfected Eucalyptus globulus (Maid et al.) Kirkp. short roots, and free‐living Pisolithus tinctorius Coker & Couch mycelia have been compared. Analysis of the soluble proteins by two dimensional polyacrylamide gel electrophoresis showed that most of the polypeptides observed in mycorrhizas were already synthesized in free‐living mycelia. The effects of mycorrhizal infection on polypeptide accumulation fell into three distinct categories: (i) decreased amounts of a large number of polypeptides, (ii) increased accumulation of a comparatively few polypeptides and, (iii) appearance of ectomycorrhizins (mycorrhiza‐specific polypeptides). Approximately 50% of the fungal polypeptides and more than 80 % of the plant polypeptides resolved on gels disappeared during the development of ectomycorrhizas. Among 520 polypeptides, 10 polypeptides, called ectomycorrhizins, were ectomycorrhiza‐specific in that they were present in ectomycorrhizas, but not in free living mycelia nor in non‐infected roots. The results showed differential accumulation of ectomycorrhizins during mycorrhiza development. These findings demonstrate that protein synthesis is drastically altered in response to the morphological and physiological changes resulting from the establishment of ectomycorrhiza.