Abstract Detail

The rise and fall of photosynthate: Evolution of plant/fungus interactions from paleobotanical and phylogenomic perspectives

Hibbett, David S. [1], Nagy, Laszlo G. [2], Floudas, Dimitrios [3].

The origin and impact of lignin decomposition in basidiomycetes.

The evolution of lignin biosynthesis was a great innovation that enabled tracheophytes to radiate on the land and create forested ecosystems. The evolution of high redox potential class II peroxidases (PODs) was a complementary innovation that enabled certain fungi to gain access to the carbohydrates embedded in heavily lignified plant cell walls. Previously, we studied the origins of PODs and other enzymes involved in decay of plant cell walls using 31 fungal genomes, including brown-rot and white-rot wood-decaying Agaricomycetes. Molecular clock analyses combined with phylogenomics suggested that the origin of white rot and PODs roughly coincided with the steep decline in the rate of organic carbon sequestration around the end of the Permo-Carboniferous. This result has been over-interpreted as meaning that the evolution of white rot Agaricomycetes "caused the end of the Carboniferous". However, other factors that may also have contributed to the reduction in coal deposition include physio-geographic shifts (contraction of extensive coastal swamp forests) and changes in plant investment in lignin, associated with decline of arboreal lycophytes and sphenophytes and expansions of seed plants. Moreover, sampling of genomes of Agaricomycetes and its sister group, Dacrymycetes (jelly fungi), was limited in the 31-genome study. Importantly, earlier decay studies suggested that some Dacrymycetes might be able to degrade lignin. We have recently expanded genome sampling, including two species of Calocera (Dacrymcyetes) and several members of early-diverging clades of Agaricomycetes (Cantharellales, Auriculariales, Phallomycetidae). No Dacrymcyete genomes possess PODs, which first appear in the Auriculariales. There are still key lineages of saprotrophic Agaricomycetes for which whole genomes are lacking, including saprotrophic Sebacinales (e.g., Craterocolla) and Cantharellales associated with white rot (Sistotrema). Nonetheless, based on the evidence at hand, it still appears that the ability degrade lignin via PODs arose about 300 million years ago. To assess the causal factors that resulted in the "end of the Carboniferous" it will be necessary to perform studies in paleoecosytem modeling that will consider the relative impact of PODs vs. paleogeographic shifts and changes in phytochemistry.

1 - Clark University, Biology, 950 Main Street, Worcester, MA, 01610, USA
2 - HAS BRC, Institute of Biochemistry, Synthetic and Systems Biology Unit, Temesvari krt 62, Szeged, 6726, Hungary
3 - Lund University, Molecular Ecology, Microbial Ecology and Evolutionary Genetics, Ecology Building, Lund University, Lund, SE-223 62, Sweden

Keywords:
lignin
wood decay fungi
genomics.

Presentation Type: Symposium Presentation
Session: SY12
Location: Hall A/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 4:45 PM
Number: SY12008
Abstract ID:1165
Candidate for Awards:None