The phytoalexins from cultivated and wild crucifers: chemistry and biology.
ABSTRACT Phytoalexins are antimicrobial secondary metabolites produced de novo by plants in response to stress, including microbial attack. In general, phytoalexins are important components of plant defenses against fungal and bacterial pathogens. The phytoalexins of crucifers are indole alkaloids derived from (S)-tryptophan, most of which contain a sulfur atom derived from cysteine. Beside their antimicrobial activity against different plant pathogenic species, cruciferous phytoalexins have shown anticarcinogenic effects on various human cell lines. This review focuses on the phytoalexins produced by cruciferous plants reported to date, with particular emphasis on their chemical synthesis, biosynthesis, metabolism by plant fungal pathogens and biological activities. A summary table containing all phytoalexins, their cultivated and wild cruciferous sources, their synthetic starting materials, biotransformation products and biological activities is provided.
- [show abstract] [hide abstract]
ABSTRACT: In plants, a host's responses to an attempted infection include activation of various secondary metabolite pathways, some of which are specific for particular plant phylogenetic clades. Phytochemicals that represent respective end products in plant immunity have been stereotypically linked to antimicrobial properties. However, in many cases, owing to the lack of unequivocal evidence for direct antibiotic action in planta, alternative functions of secondary metabolites should be considered. Correspondingly, recent findings have identified novel, and rather unexpected, functions of phytochemicals in plant immunity that mediate regulatory pathways for conserved defence responses. It also seems likely that these conserved responses can be regulated by clade-specific phytochemicals.Current opinion in plant biology 03/2012; 15(4):407-14. · 10.33 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen. To identify molecular determinants of pathogenicity we created nonpathogenic mutants of a transcription factor-coding gene, AbPf2. Frequency and timing of germination and appressorium formation on host plants were similar between the nonpathogenic ∆abpf2 mutants and wild-type A. brassicicola. The mutants were also similar in vitro to wild-type A. brassicicola in vegetative growth, conidium production, and responses to a phytoalexin, reactive oxygen species, and osmolites. The mutants' hyphae slowly grew but did not cause disease symptoms on the surface of host plants. Transcripts of the AbPf2 gene increased exponentially soon after wild-type conidia encountered their host plants. A small amount of AbPf2 protein, monitored by fused green fluorescent protein, was present in young, mature conidia. The protein level decreased during saprophytic growth, but increased and located primarily in fungal nuclei during pathogenesis. Levels of the proteins and transcripts sharply declined following colonization of host tissues beyond the initial infection site. When the transcription factor was induced in the wild type during early pathogenesis, 106 fungal genes were also induced in the wild type but not in the ∆abpf2 mutants. Notably, 33 of the 106 genes encoded secreted proteins, including eight putative effector proteins. Plants inoculated with ∆abpf2 mutants expressed higher levels of genes associated with photosynthesis, the pentose phosphate pathway, and primary metabolism, but lower levels of defense-related genes. Our results suggest that AbPf2 is an important regulator of pathogenesis, yet does not affect other cellular processes in A. brassicicola. This article is protected by copyright. All rights reserved.The Plant Journal 04/2013; · 6.58 Impact Factor