The power of synteny : deep evolutionary insights from comparative genomics

Synteny, or the order of genes in a given genome, is an emergent property of individuals and species that has only, with the implementation of next gen-sequencing, become available for evolutionary consideration. In this dissertation, I leverage syntenic information in concert with sequence data to draw connections between evolutionary mechanisms, species divergence, and trait innovation. In Chapter I, I review the major themes that ties my dissertation research together, highlighting important mechanisms at work in evolutionary complexity and introducing the system of which it will be a part. In Chapter II, I use a phylogenomic approach to better understand species relationships within the tribe. I utilize transcriptome sequences and genome derived synteny information to improve orthology detection over standard sequence similarity approaches and gain greater insight into the relationships of the tribe. I also implement differential fractionation rate orthology inference information to address gene tree-species tree incongruence. In Chapter III, as published in Abrahams et al., 2020, I utilize a microsynteny network and phylogenetic inference to investigate the origin and diversification of the MAM/IPMS gene family. I uncover unique MAM-like genes found at the orthologous locus in the Cleomaceae that shed light on the transition from IPMS to MAM. In the Brassicaceae, I identify six distinct MAM clades across Lineages I, II, and III. I characterize the evolutionary impact and consequences of local duplications, transpositions, whole genome duplications, and gene fusion events, generating several new hypotheses on the function and diversity of the MAM locus.

GreenPhylDB v5: a comparative pangenomic database for plant genomes

Comparative genomics is the analysis of genomic relationships among different species and serves as a significant base for evolutionary and functional genomic studies. GreenPhylDB (https://www.greenphyl.org) is a database designed to facilitate the exploration of gene families and homologous relationships among plant genomes, including staple crops critically important for global food security. GreenPhylDB is available since 2007, after the release of the Arabidopsis thaliana and Oryza sativa genomes and has undergone multiple releases. With the number of plant genomes currently available, it becomes challenging to select a single reference for comparative genomics studies but there is still a lack of databases taking advantage several genomes by species for orthology detection. GreenPhylDBv5 introduces the concept of comparative pangenomics by harnessing multiple genome sequences by species. We created 19 pangenes and processed them with other species still relying on one genome. In total, 46 plant species were considered to build gene families and predict their homologous relationships through phylogenetic-based analyses. In addition, since the previous publication, we rejuvenated the website and included a new set of original tools including protein-domain combination, tree topologies searches and a section for users to store their own results in order to support community curation efforts.

Inferring Orthologs: Open Questions and Perspectives

With the increasing number of sequenced genomes and their comparisons, the detection of orthologs is crucial for reliable functional annotation and evolutionary analyses of genes and species. Yet, the dynamic remodeling of genome content through gain, loss, transfer of genes, and segmental and whole-genome duplication hinders reliable orthology detection. Moreover, the lack of direct functional evidence and the questionable quality of some available genome sequences and annotations present additional difficulties to assess orthology. This article reviews the existing computational methods and their potential accuracy in the high-throughput era of genome sequencing and anticipates open questions in terms of methodology, reliability, and computation. Appropriate taxon sampling together with combination of methods based on similarity, phylogeny, synteny, and evolutionary knowledge that may help detecting speciation events appears to be the most accurate strategy. This review also raises perspectives on the potential determination of orthology throughout the whole species phylogeny.

ORTHOFOCUS: PROGRAM FOR IDENTIFICATION OF ORTHOLOGS IN MULTIPLE GENOMES IN FAMILY-FOCUSED STUDIES

The identification of orthologs to a set of known genes is often the starting point for evolutionary studies focused on gene families of interest. To date, the existing orthology detection tools (COG, InParanoid, OrthoMCL, etc.) are aimed at genome-wide ortholog identification and lack flexibility for the purposes of case studies. We developed a program OrthoFocus, which employs an extended reciprocal best hit approach to quickly search for orthologs in a pair of genomes. A group of paralogs from the input genome is used as the start for the forward search and the criterion for the reverse search, which allows handling many-to-one and many-to-many relationships. By pairwise comparison of genomes with the input species genome, OrthoFocus enables quick identification of orthologs in multiple genomes and generates a multiple alignment of orthologs so that it can further be used in phylogenetic analysis. The program is available at .