Genomic sequencing ofPhyllosticta citriasianaprovide insight into its conservation and diversification with closely relatedPhyllostictaspecies associated with citrus

Abstract

18Phyllosticta citriasiana is the causal agent of the pomelo tan spot. Here, we 19 presented the ~34Mb genome of P. citriasiana. The genome is organized in 92 20 contigs, encompassing 9202 predicted genes. Comparative genomic analyses with 21 other two Phyllosticta species (P. citricarpa and P. capitalensis) associated with citrus 22 was conducted to understand their evolutionary conservation and diversification. Pair-23 wise genome alignments revealed that these species are highly syntenic. All species 24 encode similar numbers of CAZymes and secreted proteins. However, the molecular 25 functions of the secretome showed that each species contains some enzymes with 26 distinct activities. Three Phyllosticta species shared a core set of 7261 protein 27 families. P. capitalensis had the largest set of orphan genes (2040), in complete 28 contrast to that of P. citriasiana (371) and P. citricarpa (262). Most of the orphan 29 genes were functionally unknown, but they contain a certain number of species-30 specific secreted proteins. A total of 23 secondary metabolites (SM) biosynthesis 31 clusters were identified in the three Phyllosticta species, 21 of them are highly 32 conserved among these species while the remaining 2 showed whole cluster gain and 33 loss polymorphisms or gene content polymorphisms. Taken together, our study 34 reveals insights into the genetic mechanisms of host adaptation of Phyllosticta species 35 associated with citrus and paves the way to identify effectors that function in infection 36 of citrus plants.37 38