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A new member of the pea (Pisum sativum L.) defensin gene family (DRR230-c) was isolated and characterized. In the absence of pathogen infection, transcripts from this gene and that encoding a related defensin (DRR230-a) were detected at a relatively high level in several tissues with the exception of immature pods. Expression of these genes was activated in young pods, and further elevated in mature foliar tissues, following challenge with the fungal pathogen Ascochyta pinodes, as well as with compatible, incompatible and non-host races of the bacterial pathogen Pseudomonas syringae. Induction of the defensin genes paralleled that of several known pathogenesis-related genes, including a PR-10 homolog and β-1, 3-glucanase. Pathogen-induced defensin gene activation appeared to occur only in the infected tissues, and not systemically throughout the plant. Transgenic tobacco plants expressing either of the two pea defensin genes under the control of the cauliflower mosaic virus 35S promoter were generated. When compared to partially purified peptide extracts from untransformed tobacco plants, those from transgenic plants possessed a significantly higher potential to reduce the growth of several phytopathogenic fungi in vitro. |
