Abstract
BackgroundMicro RNAs (miRs) constitute a large group of endogenous small RNAs that have crucial roles in many important plant functions. Virus infection and transgenic expression of viral proteins alter accumulation and activity of miRs and so far, most of the published evidence involves post-transcriptional regulations.ResultsUsing transgenic plants expressing a reporter gene under the promoter region of a characterized miR (P-miR164a), we monitored the reporter gene expression in different tissues and during Arabidopsis development. Strong expression was detected in both vascular tissues and hydathodes. P-miR164a activity was developmentally regulated in plants with a maximum expression at stages 1.12 to 5.1 (according to Boyes, 2001) along the transition from vegetative to reproductive growth. Upon quantification of P-miR164a-derived GUS activity after Tobacco mosaic virus Cg or Oilseed rape mosaic virus (ORMV) infection and after hormone treatments, we demonstrated that ORMV and gibberellic acid elevated P-miR164a activity. Accordingly, total mature miR164, precursor of miR164a and CUC1 mRNA (a miR164 target) levels increased after virus infection and interestingly the most severe virus (ORMV) produced the strongest promoter induction.ConclusionThis work shows for the first time that the alteration of miR pathways produced by viral infections possesses a transcriptional component. In addition, the degree of miR alteration correlates with virus severity since a more severe virus produces a stronger P-miR164a induction.
Highlights
Micro RNAs constitute a large group of endogenous small RNAs that have crucial roles in many important plant functions
AGO1 is the most important Argonaute protein in the plant Micro RNAs (miRs) pathway and preferentially binds small RNAs with a 5' terminal uridine such as most miRs [8,9,10,11]. miRs are involved in plant development, signal transduction, transcription factor accumulation, protein degradation, response to environmental stresses and pathogen invasion [12,13]. miRs are expressed at variable levels in diverse tissues and developmental stages [14,15], regulate their own biogenesis [16,17,18] and it has been reported that modest changes in miR level can result in substantial changes in the accumulation of mRNAs target genes [12,19]
In this work we showed for the first time that virus infections and GA3 treatment lead to enhanced transcriptional activity of P-miR164a revealing a novel mode of viral interference with plant miR biogenesis
Summary
Micro RNAs (miRs) constitute a large group of endogenous small RNAs that have crucial roles in many important plant functions. MiRs are expressed at variable levels in diverse tissues and developmental stages [14,15], regulate their own biogenesis [16,17,18] and it has been reported that modest changes in miR level can result in substantial changes in the accumulation of mRNAs target genes [12,19]. These facts evidence that miR expression is under a tight and fine regulation
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