Efficient virus-induced gene silencing in Arabidopsis using a 'one-step' TYMV-derived vector.

Virus-induced gene silencing (VIGS) is an important tool for the analysis of gene function in plants. This technique exploits recombinant viral vectors harbouring fragments of plant genes in their genome to generate double-stranded RNAs that initiate homology-dependent silencing of the target gene. Several viral VIGS vectors have already been successfully used in reverse-genetics studies of a variety of processes occurring in plants. Here, we show that a viral vector derived from Turnip yellow mosaic virus (TYMV) has the ability to induce VIGS in Arabidopsis thaliana, accession Col-0, provided that it carries an inverted-repeat fragment of the target gene. Robust and reliable gene silencing was observed when plants were inoculated simply by abrasion with intact plasmid DNA harbouring a cDNA copy of the viral genome, thus precluding the need for in vitro transcription, biolistic or agroinoculation procedures. Our results indicate that a 76 bp fragment is sufficient to cause gene silencing in leaves, stems and flowers, and that the TYMV-derived vector also has the ability to target genes expressed in meristematic tissues. The VIGS vector described here may thus represent an ideal tool for improving high-throughput functional genomics in Arabidopsis.

Targeted protein accumulation promoted by autoassembly and its recovery from plant cells.

The expression of a fusion protein formed between the avian infectious bronchitis virus M protein and the bacterial enzyme beta-glucuronidase (GUS) in plants promotes the formation of new organization of the endoplasmic reticulum in tobacco plants. This unusual organization of the membranes, never present in nontransformed plants, has been explained by the oligomerization of the GUS domains of the IBVM-GUS fusion proteins. These specific organized membranes could have broad implications for biotechnology since their formation could be used as a mechanism for retaining and accumulating resident proteins in specific and discrete membrane compartments. In this study, we have shown that the unusual organization of native membranes due to overexpression of the IBVM-GUS fusion gene in tobacco transgenic plants and calli is present at higher levels in plant cell suspensions than in plant tissues. In these cell suspensions, IBVM-GUS protein was continuously synthesized and accumulated throughout the cell culture. An enrichment of the chimeric IBVM-GUS protein corresponding to a five-fold increase in the microsomal fractions was achieved and the GUS enzyme did not show any modification on enzyme kinetics. However, the GUS activity could be differentially distributed in the fractions eluted at different pH suggesting differences in the surface topography of histidine residues for this recombinant GUS.

A Turnip yellow mosaic virus infection system in Arabidopsis suspension cell culture.

Turnip yellow mosaic virus (TYMV) is a positive-strand RNA virus able to infect Arabidopsis thaliana. To establish a TYMV infection system in Arabidopsis cell culture, TYMV replicons with the capsid protein gene replaced by a reporter gene expressing the Sh ble protein conferring zeocin resistance were used to transfect Arabidopsis cells. Zeocin-resistant Arabidopsis calli were used to generate a suspension cell culture. Detection of viral proteins and RNAs after 18 months in culture demonstrated persistent replication of the replicon. The Arabidopsis cell culture yielded soluble, active replication complexes, providing a useful tool to study host factors involved in TYMV replication.