Abstract
In plants, RNA interference (RNAi) plays a pivotal role in growth and development, and responses to environmental inputs, including pathogen attack. The intercellular and systemic trafficking of small interfering RNA (siRNA)/microRNA (miRNA) is a central component in this regulatory pathway. Currently, little is known with regards to the molecular agents involved in the movement of these si/miRNAs. To address this situation, we employed a biochemical approach to identify and characterize a conserved SMALL RNA-BINDING PROTEIN 1 (SRBP1) family that mediates non-cell-autonomous small RNA (sRNA) trafficking. In Arabidopsis, AtSRBP1 is a glycine-rich (GR) RNA-binding protein, also known as AtGRP7, which we show binds single-stranded siRNA. A viral vector, Zucchini yellow mosaic virus (ZYMV), was employed to functionally characterized the AtSRBP1-4 (AtGRP7/2/4/8) RNA recognition motif and GR domains. Cellular-based studies revealed the GR domain as being necessary and sufficient for SRBP1 cell-to-cell movement. Taken together, our findings provide a foundation for future research into the mechanism and function of mobile sRNA signaling agents in plants.
Highlights
The molecular mechanisms underlying the processes associated with RNA interference (RNAi) have been well characterized
To further explore the in planta function of CsSRBP1, we used the cucurbit-infecting Zucchini yellow mosaic virus (ZYMV) as a viral vector (Figure 1F), as it has been shown to be an effective tool to analyze the functions of endogenous genes, such as FLOWERING LOCUS T (Lin et al, 2007; Yoo et al, 2013)
Recognized by a DCL enzyme that generates 21-nt viral siRNA (vsiRNA) that is bound by AtSRBP1
Summary
The molecular mechanisms underlying the processes associated with RNAi have been well characterized. The fundamental agents acting in this RNAi pathway are the small interfering RNAs (siRNAs), in the 21 to 24 nucleotide (nt) size class, generated by Dicer (in animals) and DICER-LIKE (in plants) proteins, which cleave double-stranded (ds) RNAs (Bernstein et al, 2001; Kim et al, 2009). These siRNAs are incorporated into ARGONAUTE proteins (AGO) to regulate either posttranscriptional or transcriptional gene silencing (Bologna and Voinnet, 2014). The role of the phloem system in mediating the long-distance delivery
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