Potentiation of pathogen-specific defense mechanisms in Arabidopsis by beta-aminobutyric acid

The nonprotein amino acids gamma -aminobutyric acid (GABA) and beta -aminob utyric acid (BABA) have known biological effects in animals and plants. The ir mode of action has been the object of thorough research in animals but r emains unclear in plants. Our objective was to study the mode of action of BABA in the protection of Arabidopis plants against virulent pathogens. BAB A protected Arabidopsis against the oomycete pathogen Peronospora parasitic a through activation of natural defense mechanisms of the plant such as cal lose deposition, the hypersensitive response, and the formation of trailing necroses. BABA was still fully protective against P. parasitica in transge nic plants or mutants impaired in the salicylic acid, jasmonic acid, and et hylene signaling pathways. Treatment with BABA did not induce the accumulat ion of mRNA of the systemic acquired resistance (SAR)-associated PR-1 and t he ethylene- and jasmonic acid-dependent PDF1.2 genes. However, BABA potent iated the accumulation of PR-1 mRNA after attack by virulent pathogenic bac teria. As a result, BABA-treated Arabidopsis plants were less diseased comp ared with the untreated control. In the case of bacteria, BABA protected mu tants insensitive to jasmonic acid and ethylene but was not active in plant s impaired in the SAR transduction pathway. Thus, BABA protects Arabidopsis against different virulent pathogens by potentiating pathogen-specific pla nt resistance mechanisms. In addition, we provide evidence that BABA-mediat ed papilla formation after P. parasitica infection is independent of the SA R signaling pathway.