Translocation and utilization of fungal storage lipid in the arbuscular mycorrhizal symbiosis.
The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Carbon is transferred from the plant to the fungus as hexose, but the main form of carbon stored by the mycobiont at all stages of its life cycle is triacylglycerol. Previous isotopic labeling experiments showed that the fungus exports this storage lipid from the intraradical mycelium (IRM) to the extraradical mycelium (ERM). Here, in vivo multiphoton microscopy was used to observe the movement of lipid bodies through the fungal colony and to determine their sizes, distribution, and velocities. The distribution of lipid bodies along fungal hyphae suggests that they are progressively consumed as they move toward growing tips. We report the isolation and measurements of expression of an AM fungal expressed sequence tag that encodes a putative acyl-coenzyme A dehydrogenase; its deduced amino acid sequence suggests that it may function in the anabolic flux of carbon from lipid to carbohydrate. Time-lapse image sequences show lipid bodies moving in both directions along hyphae and nuclear magnetic resonance analysis of labeling patterns after supplying 13C-labeled glycerol to either extraradical hyphae or colonized roots shows that there is indeed significant bidirectional translocation between IRM and ERM. We conclude that large amounts of lipid are translocated within the AM fungal colony and that, whereas net movement is from the IRM to the ERM, there is also substantial recirculation throughout the fungus.
Bago
Berta
B
Departmento de Microbiología del Suelo y Systema Simbióticos, Estación Experimental del Zaidín, calle Profesor Albareda 1, 18008-Granada, Spain. berta.bago@uv.es
Zipfel
Warren
W
Williams
Rebecca M
RM
Jun
Jeongwon
J
Arreola
Raoul
R
Lammers
Peter J
PJ
Pfeffer
Philip E
PE
Shachar-Hill
Yair
Y
D042964:Acyl-CoA Dehydrogenase; D000595:Amino Acid Sequence; D001692:Biological Transport; D002244:Carbon / Q000378:metabolism; D020224:Expressed Sequence Tags; D044943:Fatty Acid Desaturases / Q000235:genetics* / Q000378:metabolism; D005658:Fungi / Q000201:enzymology / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic; D006601:Hexoses / Q000378:metabolism; D007553:Isotope Labeling; D050356:Lipid Metabolism; D008969:Molecular Sequence Data; D025282:Mycelium / Q000201:enzymology / Q000235:genetics; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology; D017386:Sequence Homology, Amino Acid; D012987:Soil; D013559:Symbiosis; D014280:Triglycerides / Q000378:metabolism
D006601:Hexoses; D012987:Soil; D014280:Triglycerides; D002244:Carbon; D044943:Fatty Acid Desaturases; D042964:Acyl-CoA Dehydrogenase