An Efficient Brome mosaic virus-Based Gene Silencing Protocol for Hexaploid Wheat (Triticum aestivum L.)

Inoculation of Maize with Sugarcane Mosaic Virus Constructs and Application for RNA Interference in Fall Armyworms

Virus-mediated transient gene overexpression and gene expression silencing can be used to screen gene functions in plants. Sugarcane mosaic virus (SCMV) is a positive strand RNA virus in the Potyviridae family that has been modified to be used as vector to infect monocots, including maize (Zea mays), for transient gene overexpression and gene expression silencing. Relative to stable transformation, SCMV-mediated transient expression in maize has the advantages of being faster and less expensive. Here, we describe a protocol for cloning constructs into the plasmid vector pSCMV-CS3. After maize seedlings are transformed with pSCMV-CS3 constructs by particle bombardment, the virus replicates and spreads systemically in the plants. Subsequent infections of maize seedlings can be accomplished by rub inoculation with sap from SCMV-infested plants. As an example of a practical application of the method, we also describe virus-induced gene silencing (VIGS) of fall armyworm (Spodoptera frugiperda) gene expression. Transgenic viruses are created by cloning a segment of the fall armyworm target gene into pSCMV-CS3 prior to maize transformation. Caterpillars are fed on the virus-infected maize plants, which make dsRNA to silence the expression of the fall armyworm target gene after ingestion. This use of SCMV for plant-mediated VIGS in insects allows rapid screening of gene functions when caterpillars are feeding on their host plants. Graphical overview.

Safflower Flavonoid 3′5′Hydroxylase Promotes Methyl Jasmonate-induced Anthocyanin Accumulation in Transgenic Plants

Flavonoids are the most abundant class of secondary metabolites that are ubiquitously involved in plant development and resistance to biotic and abiotic stresses. Flavonoid biosynthesis involves multiple channels of orchestrated molecular regulatory factors. Methyl jasmonate (MeJA) has been demonstrated to enhance flavonoid accumulation in numerous plant species; however, the underlying molecular mechanism of MeJA-induced flavonoid biosynthesis in safflower is still not evident. In the present study, we revealed the underlying molecular basis of a putative F3′5′H gene from safflower imparting MeJA-induced flavonoid accumulation in transgenic plants. The constitutive expression of the CtF3′5′H1 gene was validated at different flowering stages, indicating their diverse transcriptional regulation through flower development in safflower. Similarly, the CtF3′5′H1-overexpressed Arabidopsis plants exhibit a higher expression level, with significantly increased anthocyanins and flavonoid content, but less proanthocyanidins than wild-type plants. In addition, transgenic plants treated with exogenous MeJA revealed the up-regulation of CtF3′5′H1 expression over different time points with significantly enhanced anthocyanin and flavonoid content as confirmed by HPLC analysis. Moreover, CtF3′5′H1- overexpressed Arabidopsis plants under methyl violet and UV-B irradiation also indicated significant increase in the expression level of CtF3′5′H1 with improved anthocyanin and flavonoid content, respectively. Noticeably, the virus-induced gene silencing (VIGS) assay of CtF3′5′H1 in safflower leaves also confirmed reduced anthocyanin accumulation. However, the CtF3′5′H1 suppression in safflower leaves under MeJA elicitation demonstrated significant increase in total flavonoid content. Together, our findings confirmed that CtF3′5′H1 is likely mediating methyl jasmonate-induced flavonoid biosynthesis in transgenic plants via enhanced anthocyanin accumulation.

Clathrin-mediated endocytosis facilitates the internalization of Magnaporthe oryzae effectors into rice cells

Fungi and oomycetes deliver effectors into living plant cells to suppress defenses and control plant processes needed for infection. Little is known about the mechanism by which these pathogens translocate effector proteins across the plasma membrane into the plant cytoplasm. The blast fungus Magnaporthe oryzae secretes cytoplasmic effectors into a specialized biotrophic interfacial complex (BIC) before translocation. Here we show that cytoplasmic effectors within BICs are packaged into punctate membranous effector compartments that are occasionally observed in the host cytoplasm. Live cell imaging with fluorescently labeled proteins in rice (Oryza sativa) showed that these effector puncta colocalize with the plant plasma membrane and with CLATHRIN LIGHT CHAIN 1, a component of clathrin-mediated endocytosis (CME). Inhibiting CME using virus-induced gene silencing and chemical treatments resulted in cytoplasmic effectors in swollen BICs lacking effector puncta. By contrast, fluorescent marker co-localization, gene silencing and chemical inhibitor studies failed to support a major role for clathrin-independent endocytosis in effector translocation. Effector localization patterns indicated that cytoplasmic effector translocation occurs underneath appressoria before invasive hyphal growth. Taken together, this study provides evidence that cytoplasmic effector translocation is mediated by clathrin-mediated endocytosis in BICs and suggests a role for M. oryzae effectors in co-opting plant endocytosis.

Reducing the biosynthesis of condensed tannin in winged bean (Psophocarpus tetragonolobus (L.) DC.) by virus-induced gene silencing of anthocyanidin synthase (ANS) gene

The Underutilized legume-winged bean (Psophocarpus tetragonolobus (L.) DC.) and its various parts are infested with condensed tannin (CT) or proanthocyanidin (PA). CT has anti-nutritional effect as it adversely affects the digestion of proteins, minerals and vitamin among ruminants and humans. It is also responsible for low protein digestibility and decreased amino acid availability. One of the probable reasons of underutilization of P. tetragonolobus is due to its infestation with CT. Histochemical staining of various tissues of P. tetragonolobus with dimethylcinnmaldehyde (DMACA) developed a deep-blue colour indicating the presence of polyphenolic condensed tannin. Structural monomeric unit catechin and epi-catechin were reported to be responsible for biosynthesis of CT in P. tetragonolobus. The enzyme anthocyanidin synthase (ANS) and its corresponding transcripts were identified and phylogenetically mapped. The transcript was subjected to virus-induced gene silencing (VIGS) through agro-infiltration in P. tetragonolobus for reducing the CT-content. The WbANS-VIGS induced P. tetragonolobus resulted in four-fold decrease of CT as compared to the control P. tetragonolobus. A decrease of 73% of CT level was reported in VIGS silenced Wb-ANS line of P. tetragonolobus. This study resulted and confirmed that, the silencing of (ANS) gene in P. tetragonolobus has a regulatory effect on the condensed tannin biosynthesis. This study will pave way for further manipulation of ANS enzyme for reducing the biosynthesis of the anti-nutrient CT. Reducing the CT content will make this underutilized legume more acceptable.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03435-5.

A circular RNA vector for targeted plant gene silencing based on an asymptomatic viroid

Gene silencing for functional studies in plants has been largely facilitated by manipulating viral genomes with inserts from host genes to trigger virus-induced gene silencing (VIGS) against the corresponding mRNAs. However, viral genomes encode multiple proteins and can disrupt plant homeostasis by interfering with endogenous cell mechanisms. To try to circumvent this functional limitation, we have developed a silencing method based on the minimal autonomously-infectious nucleic acids currently known: viroids, which lack proven coding capability. The genome of Eggplant latent viroid, an asymptomatic viroid, was manipulated with insertions ranging between 21 and 42 nucleotides. Our results show that, although larger insertions might be tolerated, the maintenance of the secondary structure appears to be critical for viroid genome stability. Remarkably, these modified ELVd molecules are able to induce systemic infection promoting the silencing of target genes in eggplant. Inspired by the design of artificial microRNAs, we have developed a simple and standardized procedure to generate stable insertions into the ELVd genome capable of silencing a specific target gene. Analogously to VIGS, we have termed our approach viroid-induced gene silencing, and demonstrate that it is a promising tool for dissecting gene functions in eggplant.

Foxtail mosaic virus-induced gene silencing (VIGS) in switchgrass (Panicum virgatum L.)

BACKGROUND

Although the genome for the allotetraploid bioenergy crop switchgrass (Panicum virgatum) has been established, limitations in mutant resources have hampered in planta gene function studies toward crop optimization. Virus-induced gene silencing (VIGS) is a versatile technique for transient genetic studies. Here we report the implementation of foxtail mosaic virus (FoMV)-mediated gene silencing in switchgrass in above- and below-ground tissues and at different developmental stages.

RESULTS

The study demonstrated that leaf rub-inoculation is a suitable method for systemic gene silencing in switchgrass. For all three visual marker genes, Magnesium chelatase subunit D (ChlD) and I (ChlI) as well as phytoene desaturase (PDS), phenotypic changes were observed in leaves, albeit at different intensities. Gene silencing efficiency was verified by RT-PCR for all tested genes. Notably, systemic gene silencing was also observed in roots, although silencing efficiency was stronger in leaves (~ 63-94%) as compared to roots (~ 48-78%). Plants at a later developmental stage were moderately less amenable to VIGS than younger plants, but also less perturbed by the viral infection.

CONCLUSIONS

Using FoMV-mediated VIGS could be achieved in switchgrass leaves and roots, providing an alternative approach for studying gene functions and physiological traits in this important bioenergy crop.