Matthew Durrant and Shuqing Xu, Brigham Young University
Life Sciences
Researchers at the Max Planck Institute for Chemical Ecology have recently sequenced the Nicotiana attenuata (wild tobacco) genome. This genome affords researchers new opportunities to understand the evolution of this organism. One method for analyzing the evolution of specific genes in a given genome is referred to as phylostratigraphy, which makes use of large-scale BLAST sequence similarity searches. I designed a pipeline using the python programming language that implements a phylostratigraphic analysis to estimate the evolutionary age of all ~35,000 genes belonging to N. attenuata. By analyzing the large amounts of data produced by this BLAST search, each gene was assigned an estimated age through comparing the taxonomies of all other organisms that share similar protein sequences. This effectively answers the question “How old is this gene?” for each gene in the entire N. attenuata genome. Previous studies have produced microarray data that tracks the transcriptomic response of N. attenuata to an herbivore attack. By comparing the newly gathered gene evolutionary age information with this previously gathered microarray data, several new insights into the molecular signaling pathways of N. attenuata were made. It was found that at 1 hour following an herbivore attack, the transcriptome of N. attenuata is evolutionarily young, suggesting that the initial response to an herbivore attack recruits genes that have evolved more recently in the organism’s evolutionary history. At 5 hours after attack, however, there is a distinct decrease in the overall age of the N. attenuata transcriptome, suggesting that the organism is recruiting more ancient genes that are used to reconfigure the transcriptome of the organism. Beyond 5 hours, the transcriptome is once again relatively young, and it is clear that it has indeed been reconfigured to provide a more herbivore-specific defense response. This demonstrates a novel, evolutionary approach to analyzing signaling pathways in plants.