Genomic sequencing of Phyllosticta citriasiana provide insight into its conservation and diversification with closely related Phyllosticta species associated with citrus

Abstract

Phyllosticta citriasiana is the causal agent of the pomelo tan spot. Here, we presented the ~34Mb genome of P. citriasiana. The genome is organized in 92 contigs, encompassing 9202 predicted genes. Comparative genomic analyses with other two Phyllosticta species (P. citricarpa and P. capitalensis) associated with citrus was conducted to understand their evolutionary conservation and diversification. Pairwise genome alignments revealed that these species are highly syntenic. All species encode similar numbers of CAZymes and secreted proteins. However, the molecular functions of the secretome showed that each species contains some enzymes with distinct activities. Three Phyllosticta species shared a core set of 7261 protein families. P. capitalensis had the largest set of orphan genes (2040), in complete contrast to that of P. citriasiana (371) and P. citricarpa (262). Most of the orphan genes were functionally unknown, but they contain a certain number of species-specific secreted proteins. A total of 23 secondary metabolites (SM) biosynthesis clusters were identified in the three Phyllosticta species, 21 of them are highly conserved among these species while the remaining 2 showed whole cluster gain and loss polymorphisms or gene content polymorphisms. Taken together, our study reveals insights into the genetic mechanisms of host adaptation of Phyllosticta species associated with citrus and paves the way to identify effectors that function in infection of citrus plants.