Presymbiotic factors released by the arbuscular mycorrhizal fungus Gigaspora margarita induce starch accumulation in Lotus japonicus roots.
* Nutrient exchange is the key symbiotic feature of arbuscular mycorrhiza (AM). As evidence is accumulating that plants sense presymbiotic factors from AM fungi and prepare for colonization, we investigated whether modifications in plant sugar metabolism might be part of the precolonization program. * Inoculation of Lotus japonicus roots in a double Millipore sandwich with the AM fungus Gigaspora margarita prevented contact between the symbionts but allowed exchange of signal molecules. Starch content was used as a marker for root carbohydrate status. * Mycorrhizal colonization of L. japonicus roots led to a decrease in starch concentration. In roots inoculated in the double sandwich, the polysaccharide accumulated after 1 wk and persisted for at least 4 wk. The response was absent in the castor myc(-) mutant, sym4-2, while transcript levels of both CASTOR and POLLUX were slightly enhanced in the wild-type L. japonicus roots, suggesting a requirement of the corresponding proteins for the starch-accumulation response. Exudates obtained from fungal spores germinated in the absence of the plant also induced starch accumulation in wild-type L. japonicus roots. * We conclude that factors released from germinating AM fungal spores induce changes in the root carbon status, possibly by enhancing sugar import, which leads to starch accumulation when colonization is prevented.
Gutjahr
Caroline
C
Dipartimento di Biologia Vegetale, Università di Torino, Viale Mattioli 25, 10125 Torino, Italy.
Novero
Mara
M
Dipartimento di Biologia Vegetale, Università di Torino, Viale Mattioli 25, 10125 Torino, Italy.
Guether
Mike
M
Dipartimento di Biologia Vegetale, Università di Torino, Viale Mattioli 25, 10125 Torino, Italy.
Montanari
Ombretta
O
Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Golm-Potsdam, Germany.
Udvardi
Michael
M
The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
Bonfante
Paola
P
Dipartimento di Biologia Vegetale, Università di Torino, Viale Mattioli 25, 10125 Torino, Italy.
D017343:Genes, Plant; D055137:Glomeromycota / Q000378:metabolism*; D000070116:Lotus / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D038821:Mycorrhizae / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D013172:Spores, Fungal; D013213:Starch / Q000096:biosynthesis*; D013559:Symbiosis / Q000502:physiology
D010940:Plant Proteins; D011134:Polysaccharides; D013213:Starch