The auxin responsive gene Pp‐C61 is up‐regulated in Pinus pinaster roots following inoculation with ectomycorrhizal fungi
An indoleacetic acid (IAA) up-regulated cDNA, referred to as Pp-C61, was isolated by differential screening of a cDNA library constructed from auxin-treated roots of Pinus pinaster. The Pp-C61 cDNA contains a 1068 bp open reading frame which encodes a polypeptide sharing no homology with known proteins. The N-terminal protein region contains a hydrophobic signal peptide suggesting that Pp-C61 is an extracellular protein. Pp-C61 is present as a single copy in the P. pinaster genome and homologous genes were detected in other gymnosperm and angiosperm trees. Pp-C61 was transcriptionally regulated by auxin with a maximal mRNA accumulation 6 h after treatment. Pp-C61 was up-regulated by IAA concentrations as low as 10− 10m. Up-regulation was found to be a primary (direct) response to auxin. Ethylene and abscisic acid, but not quercetin were able to promote Pp-C61 mRNA accumulation. As a putative extracellular protein, Pp-C61 was postulated to play a role in ectomycorrhiza formation. Pp-C61 was up-regulated in P. pinaster roots following inoculation with ectomycorrhizal fungi. Transcript accumulation was the highest (5.5-fold over control) in the presence of an IAA-overproducing mutant of Hebeloma cylindrosporum; it was less in the presence of wild-type strains of H. cylindrosporum and Rhizopogon roseolus. Pp-C61 transcript also accumulated upon inoculation with a non-mycorrhizal mutant of H. cylindrosporum. These results suggest that Pp-C61 up-regulation corresponds to a defence reaction in response to fungal colonization.