ALD1 regulates the basal immune components and early inducible defense responses in Arabidopsis.
Nicolás M. Cecchini,Ho Won Jung,Nancy L. Engle,Timothy J. Tschaplinski,Jean T. Greenberg
2015 April 29 Molecular Plant-Microbe Interactions 28(4): 455-466
Robust immunity requires basal defense machinery to mediate timely
responses and feedback cycles to amplify defenses against potentially
spreading infections. AGD2-LIKE DEFENSE RESPONSE PROTEIN 1 (ALD1) is
needed for the accumulation of the plant defense signal salicylic acid
(SA) during the first hours after infection with the pathogen Pseudomonas syringae
and is also upregulated by infection and SA. ALD1 is an
aminotransferase with multiple substrates and products in vitro.
Pipecolic acid (Pip) is an ALD1-dependent bioactive product induced by P. syringae.
Here, we addressed roles of ALD1 in mediating defense amplification as
well as the levels and responses of basal defense machinery. ALD1 needs
immune components PAD4 and ICS1 (an SA synthesis enzyme) to confer
disease resistance, possibly through a transcriptional amplification
loop between them. Furthermore, ALD1 affects basal defense by
controlling microbial-associated molecular pattern (MAMP) receptor
levels and responsiveness. Vascular exudates from uninfected ALD1-overexpressing plants confer local immunity to the wild type and ald1
mutants yet are not enriched for Pip. We infer that, in addition to
affecting Pip accumulation, ALD1 produces non-Pip metabolites that play
roles in immunity. Thus, distinct metabolite signals controlled by the
same enzyme affect basal and early defenses versus later defense