Plant Science

Virus-based microRNA silencing (VbMS) is a viable and prompt method to screen and characterize the function of microRNAs (miRNAs) in plants. The Tobacco rattle virus (TRV)-based VbMS method was originally developed by the Yule Liu's group (Sha et al., 2014) using miRNA target mimic (TM) methodology. Here, we describe the TRV-based VbMS method for silencing endogenous miRNA in Nicotiana benthamiana and tomato via Agrobacterium infiltrations. For each assay, Agrobacterium cultures containing pTRV1 and specific pTRV2e derivative harboring TM fragments are mixed and infiltrated into plant tissues. Generally within 3 weeks, the target miRNAs gene will be silenced and the newly developed tissues will exhibit corresponding phenotypes.

microRNAs (miRNAs) are small non-coding RNAs, regulating most if not all, biological processes in eukaryotic organisms. miRNAs are initially processed from primary transcripts (pri-miRNAs) to produce miRNA precursors (pre-miRNAs), that are further processed into miRNA and its complementary strands (miRNA/*). In Arabidopsis, and possibly other plants, the processing from pri-miRNAs to pre-miRNAs and from pre-miRNAs to miRNA/* are both implemented through Dicer-like 1 (DCL1) complexes. Recently, we demonstrated isolation of DCL1 complexes of unprecedented quality from in planta. We further successfully reconstituted DCL1 cleavage assays in vitro that were able to fully recapitulate in vivo miRNA biogenesis. Here we provide a detailed protocol of DCL1 reconstitution assays. The protocol comprises three major parts (Figure 1): 1) Preparation of pri- and pre-miRNA transcripts (Procedures A-C); 2) Purification of the recombinant Arabidopsis DCL1 machinery from Nicotiana benthamiana (N. benthamiana) through immunoprecipitation (IP) (Procedures D and E); and 3) in vitro processing of radioisotope-labeled pri- or pre-miRNAs using the isolated DCL1 complexes (Procedure F). It is our desire that the protocol be a powerful tool for the RNAi community to study mechanistic issues or to develop RNA silencing technologies.

Small RNAs like microRNAs (miRNAs), small interfering RNAs (siRNAs) and other noncoding RNAs including snRNA and snoRNA have tremendous impact on eukaryotic gene regulation. Extraction of high quality small RNAs is an important prerequisite for experimental analyses of miRNAs. This will prevent RNA degradation and remove associated contaminations including polyphenols, polysaccharides and other secondary metabolites. In this protocol we describe a simple way to isolate small RNAs from the leaf tissues of Vigna mungo combining the protocols of two commercially available kits with some modifications.

This is a protocol to produce stable silencing efficacy and efficiency for VIGS using CymMV as a silencing vector for floral functional genomics in Phalaenopsis orchids. This protocol is established based on a method created by Lu et al. (2007), and then modified by Hsieh et al. (2013a; 2013b), Lu et al. (2012) successfully engineered a cloning vector (pCymMV-Gateway) in that the target gene fragment is simple to insert and can be manipulated with high efficiency. The silencing vector is inoculated into plants by Agro-inoculation by using Agrobacterium tumefaciens (A. tumefaciens) strain EHA105. Agro-infiltration of leaves for use in VIGS study of orchid flowers is a time saver and produces less damage to flower buds.

RNA-guided genome editing (RGE) using bacterial type II cluster regularly interspaced short palindromic repeats (CRISPR)–associated nuclease (Cas) has emerged as a simple and versatile tool for genome editing in many organisms including plant and crop species. In RGE based on the Streptococcus pyogenes CRISPR-Cas9 system, the Cas9 nuclease is directed by a short single guide RNA (gRNA or sgRNA) to generate double-strand breaks (DSB) at the specific sites of chromosomal DNA, thereby introducing mutations at the DSB by error-prone non-homologous end joining repairing. Cas9-gRNA recognizes targeted DNA based on complementarity between a gRNA spacer (~ 20 nt long leading sequence of gRNA) and its targeted DNA which precedes a protospacer-adjacent motif (PAM, Figure 1). In this protocol, we describe the general procedures for plant RGE using CRISPR-Cas9 system and Agrobacterium-mediated transformation. The protocol includes gRNA design, Cas9-gRNA plasmid construction and mutation detection (genotyping) for rice RGE and could be adapted for other plant species.

Plant viruses are strong inducers as well as targets of RNA silencing. In plants RNA silencing acts as a natural defense mechanism against viral infection and is associated with accumulation of virus-specific small interfering RNAs (siRNAs). The continuing discoveries, increasing awareness and interest in the regulatory roles of non-coding small RNAs have raised the need for methods that can reliably detect and quantitate the expression levels of small RNAs. Northern blot analysis of small RNAs involving the separation of RNA molecules using polyacrylamide gel electrophoresis (PAGE) has remained a popular and valuable analytical method to validate small RNAs. Northern blot analysis consist of resolving RNAs by gel electrophoresis, followed by transferring and fixing to nylon membranes as well as detecting by hybridization using radioactive probes. The following protocol provides a method for isolation and detection of small RNAs from virus-infected plants and was successfully used in Panwar et al. (2013a), Panwar et al. (2013b).