MSA - Ecology/Pathology
Hynson, Nicole , Bruns , Thomas .
Mycorrhizal specialization and its role in the evolution of myco-heterotrophy.
Myco-heterotrophy is one of the longest studies aspects of the mycorrhizal symbiosis, but there remain many critical, unanswered questions regarding the ecology and physiology of these plants and their associated fungi. Recently the determination of the stable isotope values for both carbon and nitrogen of the achlorophyllous species Pyrola aphylla (Ericaceae) revealed that this species is isotopically most similar to myco-heterotrophs that associate with ectomycorrhizal fungi. The closest green relative to P. aphylla, P. picta, also exhibits trends toward myco-heterotrophy due to the dependency of all Pyrola species on fungi to stimulate seed germination, the phylogenetic relatedness of P. picta to obligate myco-heterotrophs in the Ericaceae and, an enrichment in 15N that is similar to ericaceous myco-heterotrophs. The vast majority of all obligate myco-heterotrophs studied to date have exhibited extreme specificity for particular lineages of fungi, but it is unclear if the loss of photosynthesis is contingent upon fungal specialization. Here we examine the fungal associates of P. aphylla and P. picta to determine the pattern of mycorrhizal specialization. Our findings show that both species associate with a range of root-inhabiting fungi, the majority of which are ectomycorrhizal taxa. The association of P. picta with ectomycorrhizal fungi that are potentially shared with surrounding trees lends further support to the possibility of partial myco-heterotrophy in this species, and the lack of fungal specialization in P. aphylla provides the first example of a dicotyledonous myco-heterotroph that is a mycorrhizal generalist. Interestingly, the only other known myco-heterotrophs that are mycorrhizal generalists are albino orchids that, similar to P. aphylla, appear to have recently lost photosynthetic abilities. This indicates that although the loss of photosynthesis may not be contingent upon mycorrhizal specialization, once a plant becomes myco-heterotrophic there is strong selection pressure for it.
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Isotopic evidence of full and partial myco-heterotrophy in the plant tribe Pyroleae (Ericaceae)
1 - University of California Berkeley, Environmental Science, Policy and Management, 321 Koshland Hall, Berkeley, CA, 94720-3102, USA
2 - University of California Berkeley, Plant and Microbial Biology, 321 Koshland Hall, Berkeley, CA, 94720-3102, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood B/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 8:30 AM