β-aminobutyric acid protects Brassica napus plants from infection by Leptosphaeria maculans. Resistance induction or a direct antifungal effect?
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Resistance to infection in plants can be induced by treatment with various chemicals. One such compound is β-aminobutyric acid (BABA). Its positive effect on disease resistance has been noted in several pathosystems. Here we demonstrate that treatment with BABA protects Brassica napus plants from infection by the fungal pathogen Leptosphaeria maculans. Surprisingly, BABA also displayes in vitro antifungal activity against L. maculans with EC50 similar to the fungicide tebuconazole. Both spore germination and hyphal growth were affected. The toxic effect can be reverted by addition of trypton to the culture medium. We hypothesised that BABA might inhibit inorganic nitrogen assimilation. Suppression of disease progression in plants and antifungal activity in vitro was weaker for α-aminobutyric acid and negligible for γ-aminobutyric acid. In contrast to a resistance inducer benzothiadiazole, the effect of BABA on disease development was nearly independent of the timing of treatment, indicating possible antifungal activity in planta. On the other hand, quantification of multiple hormones and an expression analysis have shown that treatment with BABA induces a synthesis of salicylic acid (SA) and expression of SA marker gene PR-1, but no evidence was observed for priming of SA responses to L. maculans. While we have not conclusively demonstrated how BABA suppresses the disease progression, our results do indicate that antifungal activity is another mechanism by which BABA can protect plants from infection.
KeywordsAntimicrobial BTH Gene expression Pathogen Priming Salicylic acid
green fluorescent protein
liquid chromatography–mass spectrometry
We would like to thank Myrta Pařízková and Ladislav Čech for their excellent technical support, Ane Sesma for providing pCAMBgfp plasmid, and Thierry Rouxel for L. maculans isolates JN2 and JN3. This research was supported by grants from the Czech Science Foundation (522/08/1581) and the Czech Ministry of Agriculture (QH72117).
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