Phylogenomic analyses of Alternaria section Alternaria: A high-resolution, genome-wide study of lineage sorting and gene tree discordance

Abstract

The genus Alternaria contains a diversity of saprobic and pathogenic species that can be found in a wide range of environments. Alternaria is currently divided into 26 subgeneric sections, and the "small-spored" Alternaria section Alternaria includes many species that are economically important agricultural pathogens. Recognizing that a stable framework for systematics and species identification is essential for management and regulation purposes, this section has experienced much taxonomic debate and systematic revision in recent years. Molecular phylogenetic studies have challenged the reliability of using morphological characteristics to differentiate Alternaria species but have also suggested that commonly used molecular markers for fungal phylogenetics may not be sufficiently informative at this taxonomic level. To allow the assessment of molecular variation and evolutionary history at a genome-wide scale, we present an overview and analysis of phylogenomic resources for Alternaria section Alternaria. We review the currently available genomic resources and report five newly sequenced genomes. We then perform multiple comparative genomic analyses, including macrosynteny assessment and inference of phylogenetic relationships using a variety of data sets and analysis methods. Fine-scale, genome-wide phylogenetic reconstruction revealed incomplete lineage sorting and the genomic distribution of gene/species tree discordance. Based on these patterns, we propose a list of candidate genes that may be developed into informative markers that are diagnostic for the main lineages. This overview identifies gaps in knowledge and can guide future genome sequencing efforts for this important group of plant pathogenic fungi.

Keywords: Alternaria alternata; arborescens; comparative genomics; gaisen; longipes; whole-genome sequencing.