Plants treated with the non-protein amino acid beta-aminobutyric acid (BABA) develop an enhanced defensive capacity against a large variety of biotic and abiotic stresses. Expression of such BABA-induced resistance (BABA-IR) coincides with a faster and stronger defense response following pathogen attack or abiotic stress. This phenomenon has been termed “priming”. Our research group has shown previously that there is a genetic basis for the observed induced resistance and priming. We have isolated mutants that allowed the dissection of the signalling pathways involved in the phenomenon, demonstrating that BABA-IR against biotic and abiotic stresses is based on priming of distinct defense signalling mechanisms involving several plant hormone defense pathways. Recently, we have been able to show that natural priming and priming by BABA both are transgenerational phenomena, the primed state of a plant being transferred to its descendants. Beta-amino acids are rarely found in plants and up to now, BABA was considered as xenobiotic substance. However, our latest results obtained in collaboration with our colleagues from the institute of chemistry provide clear evidence that plants do synthesize BABA and its accumulation increases upon exposure to biotic and abiotic stress. This exciting result upgrades BABA to the status of a potential plant priming hormone and opens a large array of questions that will be addressed in the present proposal: • How widespread is the occurrence of BABA in plants? • Is endogenous BABA indispensable for natural priming? • What is the biosynthetic pathway of BABA production? • How is BABA biosynthesis induced and regulated? • What is the fate of BABA in plants (catabolism, storage)? • How is BABA perceived by the plant? To answer these questions, we will not only rely on our longstanding experience in plant research based techniques but we will develop novel strategies in collaboration with colleagues from organic chemistry. As an example, the biosynthetic pathway will be analysed classically by screening plant mutant populations to pinpoint the synthesis and regulatory genes of the pathway and in parallel, tools for a chemistry-based approach using radiolabeled putative precursors will be developed and exploited. The natural occurrence and inducibility of BABA in plants together with its very large spectrum of efficacy for plant priming when applied exogenously suggest that it plays an important role in the establishment of natural priming. Priming confers enhanced stress resistance with minimal inhibitory effects on yield and fitness. Interestingly, the primed state is transferred to the descendants of a primed plant. If we can identify plants that have naturally higher levels of BABA, this trait could be exploited to introduce a higher adaptive capacity to respond to stress into our agricultural ecosystems.