Tobacco Mosaic Virus Regulates the Expression of Its Own Resistance Gene N

The N gene of tobacco (Nicotiana tabacum) is a typical resistance (R) gene engendering localization of tobacco mosaic virus (TMV) infection and the elicitation of a hypersensitive necrotic response. The consensus model for R gene-derived resistance is at the level of protein:protein interactions, in which proteins of the pathogen interact with already present receptor-like proteins produced by the plant's R genes. This article demonstrates, by quantitative real-time reverse transcription-PCR analysis, that in tobacco carrying the dominant allele N, a basal level of transcription indeed occurs in noninfected plants. However, accumulation of N-mRNA in infected plants indicates that transcription is stimulated by TMV infection (up to 38-fold in locally infected leaves and up to 165-fold in upper, noninoculated leaves). Potato virus Y infection did not result in accumulation of N-mRNA, indicating a specific TMV-related phenomenon. The possible uncoupling of viral restriction from necrosis is discussed

EOBII, a Gene Encoding a Flower-Specific Regulator of Phenylpropanoid Volatiles' Biosynthesis in Petunia[C][W]

Floral scent and color play major roles in the plant's life cycle. Using petunia as a model system, a MYB-like factor was identified that transcriptionally regulates floral scent but not pigmentation. The multilayered regulation allows efficient control of metabolic flux in the phenylpropanoid pathway

Reverse Genetics of Floral Scent: Application of Tobacco Rattle Virus-Based Gene Silencing in Petunia1[OA]

Floral fragrance is responsible for attracting pollinators as well as repelling pathogens and pests. As such, it is of immense biological importance. Molecular dissection of the mechanisms underlying scent production would benefit from the use of model plant systems with big floral organs that generate an array of volatiles and that are amenable to methods of forward and reverse genetics. One candidate is petunia (Petunia hybrida), which has emerged as a convenient model system, and both RNAi and overexpression approaches using transgenes have been harnessed for the study of floral volatiles. Virus-induced gene silencing (VIGS) is characterized by a simple inoculation procedure and rapid results relative to transgenesis. Here, we demonstrate the applicability of the tobacco rattle virus-based VIGS system to studies of floral scent. Suppression of the anthocyanin pathway via chalcone synthase silencing was used as a reporter, allowing easy visual identification of anthocyaninless silenced flowers/tissues with no effect on the level of volatile emissions. Use of tobacco rattle virus constructs containing target genes involved in phenylpropanoid volatile production, fused to the chalcone synthase reporter, allowed simple identification of flowers with suppressed activity of the target genes. The applicability of VIGS was exemplified with genes encoding S-adenosyl-l-methionine:benzoic acid/salicylic acid carboxyl methyltransferase, phenylacetaldehyde synthase, and the myb transcription factor ODORANT1. Because this high-throughput reverse-genetics approach was applicable to both structural and regulatory genes responsible for volatile production, it is expected to be highly instrumental for large-scale scanning and functional characterization of novel scent genes