Chilli leaf curl virus-based vector for phloem-specific silencing of endogenous genes and overexpression of foreign genes

Geminiviruses are the largest and most devastating group of plant viruses which contain ssDNA as a genetic material. Geminivirus-derived virus-induced gene silencing (VIGS) vectors have emerged as an efficient and simple tool to study functional genomics in various plants. However, previously developed VIGS vectors have certain limitations, owing to their inability to be used in tissue-specific functional study. In the present study, we developed a Chilli leaf curl virus (ChiLCV)-based VIGS vector for its tissue-specific utilization by replacing the coat protein gene (open reading frame (ORF) AV1) with the gene of interest for phytoene desaturase (PDS) of Nicotiana benthamiana. Functional validation of ChiLCV-based VIGS in N. benthamiana resulted in systemic silencing of PDS exclusively in the phloem region of inoculated plants. Furthermore, expression of enhanced green fluorescence protein (EGFP) using the same ChiLCV vector was verified in the phloem region of the inoculated plants. Our results also suggested that, during the early phase of infection, ChiLCV was associated with the phloem region, but at later stage of pathogenesis, it can spread into the adjoining non-vascular tissues. Taken together, the newly developed ChiLCV-based vector provides an efficient and versatile tool, which can be exploited to unveil the unknown functions of several phloem-specific genes.

Development of a VIGS vector based on the β-satellite DNA associated with bhendi yellow vein mosaic virus

Bhendi yellow vein mosaic virus (BYMV) is a monopartite begomovirus with an associated β-satellite. βC1 ORF encoded by the β-satellite is the symptom determinant and a strong suppressor of post transcriptional gene silencing. To create a virus induced gene silencing vector based upon the β-satellite associated with BYVMV the βC1 ORF was replaced with multiple cloning sites. GFP transgene and plant endogenous genes Su, PDS, PCNA and AGO1 were cloned into β-satellite based VIGS vector. GFP expression was silenced in the GFP expressing transgenic 16c Nicotiana benthamiana plants infiltrated with VIGS vector carrying GFP gene inside. N. benthamiana plants infiltrated with the VIGS vector harboring the endogenous genes Su, PDS, PCNA and AGO1 produced the phenotypic symptoms yellowing of the veins, photobleaching of the veins, stunting of the plant and upward leaf curling, respectively. Real time PCR analyses revealed a reduction in the levels of the corresponding transgene or endogenous target mRNA. The β-satellite based VIGS vector was able to silence the target genes effectively. Hence, BYVMV β-satellite based VIGS vector can be used in functional genomics studies.

A dual gene-silencing vector system for monocot and dicot plants

Plant virus-based gene-silencing vectors have been extensively and successfully used to elucidate functional genomics in plants. However, only limited virus-induced gene-silencing (VIGS) vectors can be used in both monocot and dicot plants. Here, we established a dual gene-silencing vector system based on Bamboo mosaic virus (BaMV) and its satellite RNA (satBaMV). Both BaMV and satBaMV vectors could effectively silence endogenous genes in Nicotiana benthamiana and Brachypodium distachyon. The satBaMV vector could also silence the green fluorescent protein (GFP) transgene in GFP transgenic N. benthamiana. GFP transgenic plants co-agro-inoculated with BaMV and satBaMV vectors carrying sulphur and GFP genes, respectively, could simultaneously silence both genes. Moreover, the silenced plants could still survive with the silencing of genes essential for plant development such as heat-shock protein 90 (Hsp90) and Hsp70. In addition, the satBaMV- but not BaMV-based vector could enhance gene-silencing efficiency in newly emerging leaves of N. benthamiana deficient in RNA-dependant RNA polymerase 6. The dual gene-silencing vector system of BaMV and satBaMV provides a novel tool for comparative functional studies in monocot and dicot plants.