RETRACTED: RNA silencing of host transcripts by cauliflower mosaic virus requires coordinated action of the four Arabidopsis Dicer-like proteins

Abstract

RNA silencing is an ancient mechanism of gene regulation with important antiviral roles in plants and insects. Although induction of RNA silencing by RNA viruses has been well documented in plants, the interactions between DNA viruses and the host silencing machinery remain poorly understood. We investigate this question with cauliflower mosaic virus (CaMV), a dsDNA virus that expresses its genome through the polycistronic 35S RNA, which carries an unusually extensive secondary structure known as translational leader. We show that CaMV-derived siRNAs accumulate in turnip- and Arabidopsis -infected plants and that the leader is a major, albeit not exclusive, source for those molecules. Biogenesis of leader-derived siRNA requires the coordinated and hierarchical action of the four Arabidopsis Dicer-like (DCL) proteins. Our study also uncovers a “facilitating” role exerted by the microRNA biosynthetic enzyme DCL1 on accumulation of DCL2-, DCL3-, and DCL4-dependent siRNAs derived from the 35S leader. This feature of DCL1 defines a small RNA biosynthetic pathway that might have relevance for endogenous gene regulation. Several leader-derived siRNAs were found to bear near-perfect sequence complementarity to Arabidopsis transcripts, and, using a sensor transgene, we provide direct evidence that at least one of those molecules acts as a bona fide siRNA in infected turnip. Extensive bioinformatics searches identified >100 transcripts potentially targeted by CaMV-derived siRNAs, several of which are effectively down-regulated during infection. The implications of virus-directed silencing of host gene expression are discussed.

Citrus tristeza virus infection induces the accumulation of viral small RNAs (21–24-nt) mapping preferentially at the 3′-terminal region of the genomic RNA and affects the host small RNA profile

“…Supporting this latter view , the highly -structured lead er region of a DN A virus transcript has been reported as the m ajor hotspot of vsRN As (Moissiard and Voinnet 2006).…”

Diversity, evolution, and therapeutic applications of small RNAs in prokaryotic and eukaryotic immune systems

“…DCL1 acts in conjunction with DCL2, and if DCL4 is compromised, DCL2 can produce 22-nucleotide products which also can target viral mRNA [34,53]. The role of DCL2 and DCL4 in antiviral defense has been demonstrated for Cauliflower mosaic virus (CaMV) and CMV [38,102]. The loss of both DCL4 and DCL2 leads to the production of 24-nucleotide viral siRNA by DCL3 [50].…”

La bataille du silence

“…De manière surprenante, dans le triple mutant dcl2/dcl3/dcl4, la production de vsARN par DCL1 est quasiment négligeable comme cela a été précédemment observé pour les virus à ARN. À la suite de ces observations, il fut proposé que DCL1 agit précocement dans la cascade d'action des Dicer, probablement en excisant la région 35S leader du transcrit viral primaire dans un processus réminiscent de son activité nucléaire de maturation des pre-miARN [18]. Cette excision fait de l'ARNdb viral un meilleur substrat pour l'action des autres Dicer (Figure 2A).…”

“…Cette revue détaille les mécanismes du RNA silencing et de son inhibition au cours des interactions plante/ virus et suggère les possibles conséquences de cette bataille moléculaire sur l'évolution de leur génomes respectifs. < 5' du transcrit polycistronique, appelée la région « 35S leader » représente la source majoritaire de vsARN en raison de sa structure secondaire extensive qui sert de principal substrat pour Dicer [18] (Figure 2A). Ainsi, le RNA silencing peut être défini comme un système immunitaire dont un aspect fondamental est qu'il est totalement inné car la réponse est uniquement programmée par les caractéristiques et la séquence du génome infectieux et non par le génome de l'hôte lui-même.…”