Abstract Detail

Comparative Genomics/Transcriptomics

Muti, Rachel [1], Barrett, Craig [2], Sinn, Brandon [1].

Characterization of WHY1 in Corallorhiza: evolution, expression, and selection across a trophic gradient.

Mycoheterotrophy, or reliance upon fungi as an energy source, is common to all orchids at some point in their development. Species that do not conduct photosynthesis and instead parasitize fungi as their only carbon-based nutrition source are known as full mycoheterotrophs. While gene loss in the plastid and nuclear genomes due to relaxed selective pressures on photosynthetic function are well studied in mycoheterotrophs, the evolution of the molecular mechanisms controlling genome stability are completely unknown. Here I use a phylo-comparative approach to characterize the evolution of Whirly1 (WHY1), a transcription factor implicated in plastid genome stability and fungal defense, in the mycoheterotrophic orchid genus  Corallorhiza. Together, the four species studied,  C. trifida,  C. striata,  C. wisteriana, and  C. maculata, represent a trophic gradient from partial to full mycoheterotrophy. I hypothesized that  WHY1  was a single copy gene in these four  Corallorhiza  species and would be alternatively spliced and differentially expressed in aboveground inflorescence tissues and belowground rhizome tissues where the fungal host is found. This project used previously generated RNA-seq data to assemble  de novo  transcriptomes of each  Corallorhiza  species, identify  WHY1  transcripts and any non-canonical transcripts, and investigate differential expression of these transcripts in both aboveground and belowground tissues. Additionally, sampling of  WHY1  across angiosperms from public databases was conducted to provide phylogenetic context for the evolution of  WHY1  in Orchidaceae, including  Corallorhiza  and two distantly related species of fully mycoheterotrophic orchids. Screening of the  WHY1  sequence alignment of these taxonomic groups resulted in the identification of nonsynonymous substitutions specific to  Corallorhiza, and those that potentially affect structure and function are discussed. In addition, Oxford Nanopore sequencing of  Corallorhiza  WHY1  genomic sequences provided supporting evidence for intron retention as part of the alternative splicing among the transcripts. Additionally, tests of selection regime at the gene and codon level revealed relaxation of purifying selection on WHY1 in mycoheterotrophic orchids, but this signal appeared to be driven by late stage fully mycoheterotrophic species.  Overall, the results of this project suggest that pathway alteration of  WHY1  precedes the establishment of potentially deleterious substitutions and reveal that splicing alteration and decreased expression of  WHY1  are coincidental with the shift to full mycoheterotrophy.

1 - Otterbein University, Dept. of Biology and Earth Science, Biochemistry and Molecular Biology Program, 1 South Grove Street, Westerville, OH, 43081, USA
2 - West Virginia University, Dept. of Biology, 53 Campus Drive, Morgantown, WV, 26506, USA

Keywords:
Corallorhiza
WHY1
Whirly transcription factors
mycoheterotrophy
alternative splicing
nonsynonymous substitutions
differential gene expression.

Presentation Type: Oral Paper
Session: CGT2, Comparative Genomics/Transcriptomics II
Location: /
Date: Tuesday, July 20th, 2021
Time: 2:00 PM(EDT)
Number: CGT2007
Abstract ID:525
Candidate for Awards:Margaret Menzel Award