A single amino acid transporter controls the uptake of priming-inducing beta-amino acids and the associated trade-off between induced resistance and plant growth

ABSTRACT Selected beta-amino acids, such as beta-aminobutyric acid (BABA) and R-beta-homoserine (RBH), can prime plants for resistance against broad-spectrum diseases. Here, we describe a genome-wide screen of fully annotated Arabidopsis T-DNA insertion lines for impaired in RBH-induced immunity ( iri ) against the downy mildew pathogen Hyaloperonospora arabidopsidis , yielding 104 lines that were partially affected and 4 lines that were completely impaired in RBH-induced resistance. The iri1-1 mutant phenotype could be confirmed by an independent T-DNA insertion in the same gene, encoding the high-affinity amino acid transporter LHT1. Using uptake experiments with IRI1/LHT1 -expressing yeast cells and mass spectrometry-based quantification of RBH and BABA in leaves of mutant and over-expression lines of IRI1/LHT1 , we demonstrate that IRI1/LHT1 acts as the main transporter for cellular uptake and systemic distribution of RBH and BABA. Subsequent characterisation of mutant and over-expression lines of IRI1/LHT1 for induced resistance and growth responses revealed that the level of IRI1/LHT1 expression determines the trade-off between induced resistance and plant growth by RBH and BABA.