Plant Pathology Seminar Series “Clues about the evolution of mycoheterotrophy through the lens of Dutchman’s pipe (Monotropa hypopitys)” Alex Batson Without a means of photosynthesis, achlorophyllous plants obtain nutrients either from fungi or by direct parasitism of autotrophic plants (Leake 1994). Plants that are fully reliant on mycorrhizal or saprophytic fungi for carbon-based nutrition are referred to as mycoheterotrophic (Leake 1994). In addition to being devoid of chlorophyll, mycoheterotrophic plants have scale-like or greatly reduced leaves, produce minute, dust-like seeds, often lack stomata, have reduced vascular systems, and their roots generally form in tight balls or are greatly reduced in form (Furman and Trappe 1971; Leake 1994). Historically, mycoheterotrophic plants were believed to be saprophytes of leaf litter. However, studies that investigated the association of fungi and Monotropa hypopitys (Dutchman’s pipe, Ericaceae) found that the roots were colonized consistently by mycorrhizal Tricholoma spp. (Bidartondo and Bruns 2001; Leake et al. 2004). Using 14C and 32P, mycoheterotrophic plants were demonstrated to obtain nutrients from neighboring autotrophic plants through mutual mycorrhizal associations (Björkman 1960). Trudell et al. (2003) corroborated this by demonstrating that M. hypopitys and other mycoheterotrophic plants were enriched for stable isotopes of 13C and 15N relative to that of neighboring autotrophic plants. It is unclear how the specific relationship between M. hypopitys and Tricholoma spp. evolved. However, it has been hypothesized that dependency of the plant on a fungal partner represents transition from partial reliance on a fugal partner (mixotrophy) to full reliance, as a result of selection pressure in shaded, understory forests (Tedersoo et al. 2007). The chloroplast genome of M. hypopitys is greatly reduced and lacks all genes that encode photosynthetic functions, which may reflect the transition from mixotrophy to mycoheterotrophy (Gruzdev et al. 2016). The interactions between mycoheterotrophic plants, such as Dutchman’s pipe, and their associated fungal partners remain poorly understood, including the genetic mechanisms facilitating mycoheterotroph-partner specificity, the transfer of nutrients between partners, and whether there is any benefit to the fungal partner and/or autotrophic partner engaged in this relationship. 4:10 pm | Monday, August 27 | Johnson Hall 343 Plant Pathology 515, Fall 2018 References Bidartondo, M. I. and Bruns, T. D. 2001. Fine-level mycorrhizal specificity in the Monotropoideae (Ericaceae): specificity for fungal species groups. Mol. Ecol. 10:2285-2295. Björkman, E. 1960. Monotropa hypopitys L. – an epiparisite on tree roots. Physiol. Plantarum 13:308-327. Furman, T. E. and Trappe, J. M. 1971. Phylogeny and ecology of mycotrophic achlorophyllous angiosperms. Quart. Rev. Biol. 46:219-225. Gruzdev, E. V., Mardanov, A. V., Beletsky, A. V., Kochieva, E. Z., Ravin, N. V., and Skryabin, K. G. 2016. The complete chloroplast genome of parasitic flowering plant Monotropa hypopitys: extensive gene losses and size reduction. Mitoch. DNA Part B 1:212-213. Leake, J. 1994. The biology of myco-heterotrophic (‘saprophytic’) plants. New Phytol. 127:171-216. Leake, J. R., McKendrick, S. I., Bidartondo, M., and Read, D. J. 2004. Symbiotic germination and development of the myco-heterotroph Monotropa hypopitys in nature and its requirement for locally distributed Tricholoma spp. New Phytol. 163:405-423. Tedersoo, L., Pellet, P., Kõljalg, U., and Selosse, M. 2007. Parallel evolutionary paths to mycoheterotrophy in understorey Ericaceae and Orchidaceae: ecological evidence for mixotrophy in Pyrolea. Oecologia 151:206-217. Trudell, S. A., Rygiewicz, P. T., and Edmonds, R. L. 2003. Nitrogen and carbon stable isotope abundances support the myco-heterotrophic nature and host-specificity of certain achlorophyllous plants. New Phytol. 160:391-401. .