Viral suppressor of RNA silencing in vascular plants also interferes with the development of the bryophyte Physcomitrella patens

Plant viruses are important pathogens able to overcome plant defense mechanisms using their viral suppressors of RNA silencing (VSR). Small RNA pathways of bryophytes and vascular plants have significant similarities, but little is known about how viruses interact with mosses. This study elucidated the responses of Physcomitrella patens to two different VSRs. We transformed P. patens plants to express VSR P19 from tomato bushy stunt virus and VSR 2b from cucumber mosaic virus, respectively. RNA sequencing and quantitative PCR were used to detect the effects of VSRs on gene expression. Small RNA (sRNA) sequencing was used to estimate the influences of VSRs on the sRNA pool of P. patens. Expression of either VSR-encoding gene caused developmental disorders in P. patens. The transcripts of four different transcription factors (AP2/erf, EREB-11 and two MYBs) accumulated in the P19 lines. sRNA sequencing revealed that VSR P19 significantly changed the microRNA pool in P. patens. Our results suggest that VSR P19 is functional in P. patens and affects the abundance of specific microRNAs interfering with gene expression. The results open new opportunities for using Physcomitrella as an alternative system to study plant-virus interactions.