Symposium V: From the soil to the seed
Abs #
50002: The arbuscular mycorrhizal symbiosis and phosphorus acquisition
In natural ecosystems, most vascular flowering plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. These mutually beneficial associations develop in the roots, where the fungus colonizes the cortex to obtain carbon from the plant. In addition to inhabiting the root, the fungus establishes hyphal networks in the soil, via which phosphorus and other mineral nutrients are transferred to the root. Thus the symbiosis has a significant impact on plant mineral nutrition and consequently on plant health. Fossil evidence suggests that plants have been associated with AM fungi since they first colonized land and today, AM symbioses are formed by almost all vascular flowering plant species. The symbiosis is a highly compatible partnership, in which both symbionts differentiate to develop specialized symbiotic interfaces (arbuscule-cortical cell) over which phosphate is transported. The research in my lab focuses on the mechanisms underlying development of the AM symbiosis and symbiotic phosphate transport. A legume, Medicago truncatula, and an AM fungus, Glomus versiforme are used for these analyses.
To gain insight into the transcriptional networks that are activated during development of the symbiosis, ESTs were generated and transcript profiles were examined using cDNA arrays. Of the genes showing elevated transcript levels, most appeared to be responding to the AM fungus, rather than to the secondary effects of increased phosphorus nutrition. The mycorrhiza-induced gene sets included a significant proportion of putative signaling proteins, suggesting that novel signaling pathways are activated in the symbiosis. Currently a 16K oligonucleotide-based array is being used to survey transcript profiles in M. truncatula mycorrhiza mutants, to further define the transcriptional events that underlie development of the AM symbiosis.
The M. truncatula EST collections, available through http://www.medicago.org/ or http://www.tigr.org/tigr-scripts/tgi/T_index.cgi?species=medicago, contain approximately 190,000 ESTs. Motif searching strategies enabled the identification of a mycorrhiza-specific phosphate transporter, MtPT4 that is expressed exclusively in mycorrhizal roots. The MtPT4 protein is located in the peri-arbuscular membrane, where a function in symbiotic phosphate transport in predicted. RNAi approaches are in progress to evaluate the roles of MtPT4 and the other mycorrhiza-regulated genes in the symbiosis.
