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Brassica oleracea-Alternaria brassicicola interaction during the early stages of leaf infection

ABSTRACT: Gene expression changes during the initial stages of black spot disease caused by Alternaria brassicicola on Brassica oleracea (Brassica oleracea var. capitata f. alba, white cabbage) leaves were investigated with Arabidopsis thaliana oligonucleotide microarrays. Transcriptional profiling of infected B. oleracea leaves revealed that photosynthesis was the most negatively regulated biological process. The negative regulation of 6 photosynthesis-related genes, mainly the genes involved in the photosynthesis light reaction and Calvin cycle, was observed as early as 12 hours post infection (hpi). It progressed through 48-hpi stage, when 44 down-regulated photosynthesis-related genes were detected. The analyses of infected leaves at microscopic, ultrastructural and physiological levels supported the microarray-based observations and indicated that the photosynthetic processes are suppressed in B. oleracea as a result of the fungal infection.

ORGANISM(S): Arabidopsis thaliana Brassica oleracea var. capitata

PROVIDER: GSE155051 | GEO | 2020/07/25

REPOSITORIES: GEO

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Project description:Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen. Molecular determinants of its life style shift between saprophyte and pathogen, however, are unknown. To identify these determinants we studied 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 Δabpf2 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 chemical stressors, such as a phytoalexin, reactive oxygen species, and osmolites. The mutants, however, did not penetrate host plant tissues, though their hyphae continued to grow on the plant surface. 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 located in both the cytoplasm and nuclei of young, mature conidia. The protein level decreased during saprophytic growth but increased several-fold during pathogenesis. Levels of both the proteins and transcripts sharply declined following colonization of host tissues beyond the initial infection site. When the transcription factor was expressed at an induced level in the wild type during early pathogenesis, the expression of 106 fungal genes was down-regulated in the Δabpf2 mutants. Notably, 33 of the 106 genes encoded secreted proteins, including eight putative effector proteins. Plants inoculated with Δabpf2 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 conidia of A. brassicicola are programmed as saprophytes, but become parasites upon contact with their hosts. AbPf2 coordinates this transformation by expressing pathogenesis-associated genes, including those coding for effectors.

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Brassica oleracea-Alternaria brassicicola interaction during the early stages of leaf infection

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