Citrus psorosis virus 24 K protein interacts with citrus miRNA precursors, affects their processing and subsequent miRNA accumulation and target expression

Summary Sweet orange ( C itrus sinensis ), one of the most important fruit crops worldwide, may suffer from disease symptoms induced by virus infections, thus resulting in dramatic economic losses. Here, we show that the infection of sweet orange plants with two isolates of C itrus psorosis virus ( CPsV ) expressing different symptomatology alters the accumulation of a set of endogenous microRNAs ( miRNAs ). Within these miRNAs , miR156 , miR167 and miR171 were the most down‐regulated, with almost a three‐fold reduction in infected samples. This down‐regulation led to a concomitant up‐regulation of some of their targets, such as S quamosa promoter‐binding protein‐like 9 and 13 , as well as S carecrow‐like 6 . The processing of miRNA precursors, pre‐mi R 156 and pre‐mi R 171, in sweet orange seems to be affected by the virus. For instance, virus infection increases the level of unprocessed precursors, which is accompanied by a concomitant decrease in mature species accumulation. miR156 a primary transcript accumulation remained unaltered, thus strongly suggesting a processing deregulation for this transcript. The co‐immunoprecipitation of viral 24 K protein with pre‐mi R 156 a or pre‐mi R 171 a suggests that the alteration in the processing of these precursors might be caused by a direct or indirect interaction with this particular viral protein. This result is also consistent with the nuclear localization of both miRNA precursors and the CPsV 24 K protein. This study contributes to the understanding of the manner in which a virus can alter host regulatory mechanisms, particularly miRNA biogenesis and target expression.