Abstract
Transitivity in plants is a mechanism that produces secondary small interfering RNAs (siRNAs) from a transcript targeted by primary small RNAs (sRNAs). It expands the silencing signal to additional sequences of the transcript. The process requires RNA-dependent RNA polymerases (RDRs), which convert single-stranded RNA targets into a double-stranded (ds) RNA, the precursor of siRNAs and is critical for effective and amplified responses to virus infection. It is also important for the production of endogenous secondary siRNAs, such as phased siRNAs (phasiRNAs), which regulate several genes involved in development and adaptation. Transitivity on endogenous transcripts is very specific, utilizing special primary sRNAs, such as miRNAs with unique features, and particular ARGONAUTEs. In contrast, transitivity on transgene and virus (exogenous) transcripts is more generic. This dichotomy of responses implies the existence of a mechanism that differentiates self from non-self targets. In this work, we examine the possible mechanistic process behind the dichotomy and the intriguing counter-intuitive directionality of transitive sequence-spread in plants.
Highlights
The proper regulation of gene expression is essential for the development and the adaptation of plants to their environment
DCL4 is dominant over DCL2, much lower levels of 22 nt than 21 nt small interfering RNAs (siRNAs) are produced in the normal situation of both DICER-LIKE enzymes (DCLs) being present (Gasciolli et al, 2005; Xie et al, 2005; Deleris et al, 2006; Fusaro et al, 2006; Moissiard et al, 2007); and secondly, in contrast to miRNAs, siRNA-triggered transitivity is very limited when the target mRNA is from an endogene compared to the situation with transgenic transcripts or viral RNA (Figure 1B) (Vaistij et al, 2002; Himber et al, 2003; Kościań ska et al, 2005; Miki et al, 2005; Petersen and Albrechtsen, 2005; Bleys et al, 2006b; Aregger et al, 2012)
A significant fraction of RNA-dependent RNA polymerase 6 (RDR6)-dependent RNA synthesis would not reach regions that are too far from the transcription beginning, even if the sequence is within range of the enzyme activity, due to early disassociation of the polymerase from the template (Figure 2B)
Summary
Transitivity in plants is a mechanism that produces secondary small interfering RNAs (siRNAs) from a transcript targeted by primary small RNAs (sRNAs). The process requires RNAdependent RNA polymerases (RDRs), which convert single-stranded RNA targets into a double-stranded (ds) RNA, the precursor of siRNAs and is critical for effective and amplified responses to virus infection. It is important for the production of endogenous secondary siRNAs, such as phased siRNAs (phasiRNAs), which regulate several genes involved in development and adaptation. Transitivity on transgene and virus (exogenous) transcripts is more generic This dichotomy of responses implies the existence of a mechanism that differentiates self from non-self targets.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
