The auxin-inducible GH3 homologue Pp-GH3.16 is downregulated in Pinus pinaster root systems on ectomycorrhizal symbiosis establishment.
In an attempt to determine whether auxin-regulated plant genes play a role in ectomycorrhizal symbiosis establishment, we screened a Pinus pinaster root cDNA library for auxin-upregulated genes. This allowed the identification of a cDNA, Pp-GH3.16, which encodes a polypeptide sharing extensive homologies with GH3 proteins of different plants. Pp-GH3.16 was specifically upregulated by auxins and was not affected by cytokinin, gibberellin, abscisic acid or ethylene, or by heat shock, water stress or anoxia. Pp-GH3.16 mRNAs were quantified in pine roots inoculated with two ectomycorrhizal fungi, Hebeloma cylindrosporum and Rhizopogon roseolus. Surprisingly, Pp-GH3.16 was downregulated following inoculation with both fungal species. The downregulation was most rapid on establishment of symbiosis with an indole-3-acetic acid (IAA)-overproducing mutant of H. cylindrosporum, which overproduced mycorrhizas characterized by a hypertrophic Hartig net. This indicates that, despite being auxin-inducible, Pp-GH3.16 can be downregulated on establishment of symbiosis with a fungus that releases auxin. By contrast, Pp-GH3.16 was not downregulated in pine root systems inoculated with a nonmycorrhizal mutant of H. cylindrosporum, suggesting that the downregulation we observed in mycorrhizal root systems was a component of the molecular cross-talk between symbiotic partners at the origin of differentiation of symbiotic structures.
Reddy
S M
SM
Université Lyon 1, UMR CNRS 5557, USC INRA 1193 d'Ecologie Microbienne Bât. A. Lwoff, 43 boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.
Hitchin
S
S
Melayah
D
D
Pandey
A K
AK
Raffier
C
C
Henderson
J
J
Marmeisse
R
R
Gay
G
G
D000363:Agaricales / Q000502:physiology; D000595:Amino Acid Sequence; D001487:Basidiomycota / Q000502:physiology; D003001:Cloning, Molecular; D003513:Cycloheximide / Q000494:pharmacology; D015536:Down-Regulation; D015723:Gene Library; D007210:Indoleacetic Acids / Q000494:pharmacology*; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000502:physiology*; D028223:Pinus / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D012333:RNA, Messenger / Q000378:metabolism; D016415:Sequence Alignment; D013559:Symbiosis / Q000235:genetics*; D015854:Up-Regulation
D007210:Indoleacetic Acids; D010940:Plant Proteins; D012333:RNA, Messenger; D003513:Cycloheximide