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Transcriptional reprogramming plays a significant role in governing plant responses to pathogens. The underlying regulatory networks are complex and dynamic, responding to numerous input signals. Most network modelling studies to date have used large-scale expression data sets from public repositories but defence network models with predictive ability have also been inferred from single time series data sets, and sophisticated biological insights generated from focused experiments containing multiple network perturbations. Using multiple network inference methods, or combining network inference with additional data, such as promoter motifs, can enhance the ability of the model to predict gene function or regulatory relationships. Network topology can highlight key signaling components and provides a systems level understanding of plant defence. [ABSTRACT FROM AUTHOR]

Examines the signalling pathways underlying disease resistance to specific groups of pathogens in Arabidopsis and discusses the application of the emerging trends to the study of plant pathology in South Africa. Discussion on salicylic acid (SA)-dependent defence responses; SA-independent defence responses; Complexity of disease resistance signalling in Arabidopsis.

The article reports on plants' evolved systems of immunity such as the pathogen-associated molecular patterns (PAMP) detection, which serve as a warning for the presence of pathogens. PAMP binds to pattern recognition receptor resulting to the induction of basal defense systems. Pathogens fight back with evolved effectors resulting to evolution of cultivar-specific resistance in plants as a defense.

Numerous studies have suggested that plant/pathogen interactions are partially mediated via plant secondary metabolite production and corresponding pathogen tolerance. However, there are inconsistent reports on the ability of particular compounds to provide resistance to a pathogen. Most of these studies have focused on individual isolates of a given pathogen, suggesting that pathogens vary in their sensitivity to plant-produced toxins. We tested variability in virulence among pathogen isolates, and the impact on this by plant production of, and pathogen tolerance to, secondary metabolites. Botrytis cinerea isolates showed differing sensitivity to purified camalexin, and camalexin-sensitive isolates produced larger lesions on camalexin-deficient Arabidopsis genotypes than on the wild type. In contrast, the camalexin-insensitive isolate produced lesions of similar size on wild-type and camalexin-deficient Arabidopsis. Additional analysis with Arabidopsis secondary metabolite biosynthetic mutants suggests that Botrytis also has variable sensitivity to phenylpropanoids and glucosinolates. Furthermore, Botrytis infection generates a gradient of secondary metabolite responses emanating from the developing lesion, with the Botrytis isolate used determining the accumulation pattern. Collectively, our results indicate that Arabidopsis/ Botrytis interactions are influenced at the metabolic level by variations in toxin production in the host and sensitivity in the pathogen. [ABSTRACT FROM AUTHOR]

The circadian clock, an internal time-keeping mechanism, allows plants to anticipate regular changes in the environment, such as light and dark, and biotic challenges such as pathogens and herbivores. Here, we demonstrate that the plant circadian clock influences susceptibility to the necrotrophic fungal pathogen, Botrytis cinerea. Arabidopsis plants show differential susceptibility to B. cinerea depending on the time of day of inoculation. Decreased susceptibility after inoculation at dawn compared with night persists under constant light conditions and is disrupted in dysfunctional clock mutants, demonstrating the role of the plant clock in driving time-of-day susceptibility to B. cinerea. The decreased susceptibility to B. cinerea following inoculation at subjective dawn was associated with faster transcriptional reprogramming of the defence response with gating of infection-responsive genes apparent. Direct target genes of core clock regulators were enriched among the transcription factors that responded more rapidly to infection at subjective dawn than subjective night, suggesting an influence of the clock on the defence-signalling network. In addition, jasmonate signalling plays a crucial role in the rhythmic susceptibility of Arabidopsis to B. cinerea with the enhanced susceptibility to this pathogen at subjective night lost in a jaz6 mutant. [ABSTRACT FROM AUTHOR]