The ectomycorrhizal fungus Laccaria bicolor stimulates lateral root formation in poplar and Arabidopsis through auxin transport and signaling.
The early phase of the interaction between tree roots and ectomycorrhizal fungi, prior to symbiosis establishment, is accompanied by a stimulation of lateral root (LR) development. We aimed to identify gene networks that regulate LR development during the early signal exchanges between poplar (Populus tremula x Populus alba) and the ectomycorrhizal fungus Laccaria bicolor with a focus on auxin transport and signaling pathways. Our data demonstrated that increased LR development in poplar and Arabidopsis (Arabidopsis thaliana) interacting with L. bicolor is not dependent on the ability of the plant to form ectomycorrhizae. LR stimulation paralleled an increase in auxin accumulation at root apices. Blocking plant polar auxin transport with 1-naphthylphthalamic acid inhibited LR development and auxin accumulation. An oligoarray-based transcript profile of poplar roots exposed to molecules released by L. bicolor revealed the differential expression of 2,945 genes, including several components of polar auxin transport (PtaPIN and PtaAUX genes), auxin conjugation (PtaGH3 genes), and auxin signaling (PtaIAA genes). Transcripts of PtaPIN9, the homolog of Arabidopsis AtPIN2, and several PtaIAAs accumulated specifically during the early interaction phase. Expression of these rapidly induced genes was repressed by 1-naphthylphthalamic acid. Accordingly, LR stimulation upon contact with L. bicolor in Arabidopsis transgenic plants defective in homologs of these genes was decreased or absent. Furthermore, in Arabidopsis pin2, the root apical auxin increase during contact with the fungus was modified. We propose a model in which fungus-induced auxin accumulation at the root apex stimulates LR formation through a mechanism involving PtaPIN9-dependent auxin redistribution together with PtaIAA-based auxin signaling.
Felten
Judith
J
UMR INRA/Nancy Université 1136 Interactions Arbres/Micro-organismes, Institut Fédératif de Recherche 110 Genomique, Ecophysiologie, et Ecologie Fonctionnelles, INRA Nancy, F-54280 Champenoux, France.
Kohler
Annegret
A
Morin
Emmanuelle
E
Bhalerao
Rishikesh P
RP
Palme
Klaus
K
Martin
Francis
F
Ditengou
Franck A
FA
Legué
Valérie
V
D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology*; D001692:Biological Transport / Q000187:drug effects; D016764:Cell Polarity / Q000187:drug effects; D015169:Colony Count, Microbial; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism*; D055399:Laccaria / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D038821:Mycorrhizae / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D010797:Phthalimides / Q000494:pharmacology; D032107:Populus / Q000166:cytology / Q000235:genetics / Q000254:growth & development* / Q000382:microbiology*; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
D007210:Indoleacetic Acids; D010797:Phthalimides; C002687:alpha-naphthylphthalamic acid