The xenobiotic β-aminobutyric acid enhances Arabidopsis thermotolerance

The non-protein amino acid beta-aminobutyric acid (BABA) primes Arabidopsis to respond more quickly and strongly to pathogen and osmotic stress. Here, we report that BABA also significantly enhances acquired thermotolerance in Arabidopsis. This thermotolerance was dependent on heat shock protein 101, a critical component of the normal heat-shock response. BABA did not enhance basal thermotolerance under a severe heat-shock treatment. No roles for the hormones ethylene and salicylic acid in BABA-induced acquired thermotolerance were identified by mutant analysis. Using global gene expression analysis, transcript levels for several transcription factors and DNA binding proteins regulating responses to the stress hormone abscisic acid (ABA) were found to be elevated in BABA-treated plants compared with water-treated plants. The role of ABA in BABA-induced thermotolerance was complex. BABA-enhanced thermotolerance was partially compromised in the ABA-insensitive mutant, abi1-1, but was augmented in abi2-1. In an unrelated process, BABA, like ABA, inhibited root growth, and the level of inhibition was roughly additive in roots treated with both compounds. Root growth of both abi1-1 and abi2-1 was also inhibited by BABA. Unexpectedly, abi1-1 and abi2-1 root growth was inhibited more strongly by combined ABA and BABA treatments than by BABA alone. Our results, together with previously published data, suggest that BABA is a general enhancer of plant stress resistance, and that cross-talk occurs between BABA and ABA signalling cascades. Specifically, the BABA-mediated accumulation of ABA transcription factors without concomitant activation of a downstream ABA response could represent one component of the BABA-primed state in Arabidopsis.