A brief overview of the size and composition of the myrtle rust genome and its taxonomic status

Abstract

Using de novo assembly of 46 million paired end sequence reads of length 250 bp for a myrtle rust isolate, we have estimated its genome size to be between 103 and 145 Mb and the number of proteins as >19,000. Annotation of the contigs found a very large percentage of proteins are associated with molecular functions of DNA binding or binding in biological processes for DNA integration and RNA-dependent DNA replication. A large proportion of these activities are attributed to the transposable elements (TEs). These elements are estimated to comprise 27% of the genome with 22% retrotransposons and 5% DNA transposons. The exon and intron boundaries of 46 genes occurring on contigs >20,000 bp have been determined. The number of introns range from 2 to 20 with a mean of 7. Phylogenetic analyses using partial COXI, 18S rRNA and 28S rRNA genes have placed myrtle rust in the Pucciniaceae lineage on a separate taxonomic branch from the families of Pucciniaceae, Phragmidiaceae, Sphaerophragmiaceae, Phragmidiaceae, Uropyxidaceae, Chaconiaceae and Phakopsoraceae. Further work is thus required to determine the family placement of myrtle rust in the Pucciniaceae of Pucciniales.