Accumulation patterns of endogenous β-aminobutyric acid during plant development and defense in Arabidopsis thaliana.

We have recently discovered that β-aminobutyric acid (BABA), a molecule known for its ability to prime defenses in plants, is a natural plant metabolite. However, the role played by endogenous BABA in plants is currently unknown. In this study we investigated the systemic accumulation of BABA during pathogen infection, the levels of BABA during plant growth and development, and analyzed mutants possibly involved in BABA transport or regulation. BABA was quantified by LC-MS using an improved method adapted from a previously published protocol. Systemic accumulation of BABA was determined by analyzing non-infected leaves and roots after localized infections with Plectosphaerella cucumerina or Pseudomonas syringae pv. tomato (Pst) DC3000 avrRpt2. The levels of BABA were also quantified in different plant tissues and organs during normal plant growth, and in leaves during senescence. Mutants affecting amino acid transport (aap6, aap3, prot1, and gat1), γ-aminobutyric acid levels (pop2), and senescence/defense (cpr5-2) were analyzed. BABA was found to accumulate only locally after bacterial or fungal infection, with no detectable increase in non-infected systemic plant parts. In leaves, the BABA content increased during natural and induced senescence. Reproductive organs were found to show the highest levels of BABA, and the mutant cpr5-2 was found to produce constitutively high levels of BABA. Synthetic BABA is highly mobile in the receiving plant, whereas endogenous BABA appears to be produced and accumulated locally in a tissue-specific way. We discuss a possible role for BABA in the age-related resistance, and propose a comprehensive model for endogenous and synthetic BABA. This article is protected by copyright. All rights reserved.