Nigromargarita tarda gen. et sp. nov. and distribution of an intron position class within Pleosporales

Pleosporales , the largest order in Dothideomycetes, has a broad host range and inhabits host plants as epiphytes, endophytes, parasites and saprophytes. Trematosphaeriaceae is a monophyletic family in Pleosporales, composed of species of deviated ecological background and morphological traits. In this study, we described a new fungal taxon under Trematosphaeriaceae, based on root endophytic fungi recovered from the desert plant Gymnocarpos przewalskii in Gansu Province, China. The taxon is characterised by simple, aseptate conidia and pycnidia in unusually small sizes. Multilocus phylogenetic analysis, based on ITS, LSU, SSU and TEF sequences and a morphology study indicated that the taxon represented a new genus within the Trematosphaeriaceae and was named Nigromargarita tarda. Intriguingly, an intron of 355 bp in length located at site 453 on the ribosomal SSU gene was detected in one strain of N. tarda. Sequence analysis and phylogenetic analysis indicated that the intron belongs to an intron position class (Pcl) restricted to Pleosporales. Phylogeny affiliated distribution of this Pcl was confined at the genus or lower level, suggesting a horizontal transmission pattern of this Pcl. This study established a new genus in Trematosphaeriaceae and depicted the spread features of a less-documented Pcl amongst Pleosporales families with high resolution, which promotes our understanding of the origin and transmission mechanism of such mobile genetic elements.