Azelaic acid-conferred defense priming in Arabidopsis.

CECCHINI NM; BEST M; GIFFORD AN; KIM A; SUNG WON; FOWLER JS; GREENBERG JT

Congreso; Molecular Biosciences Annual Retreat, Division of Biological Sciences, University of Chicago.; 2012

Priming of defense responses could be a major mechanism behind the immunological ?memory? observed during plant systemic acquired resistance (SAR). A lipidic signal, azelaic acid (AZA) was identified as a key mobile priming factor. AZA treatment induces the essential SAR-component AZI1 and DIR1. The products of these genes are lipid transfer proteins (LTPs) suggesting that AZA, or an AZA-derivative, could be bound and translocated by AZI1 and/or DIR1. To discern the role of these LTPs in AZA-conferred priming we analyzed two key aspects: how AZI1/DIR1 affects AZA movement and AZI1/DIR1 subcellular locations.Using phloem uploading assays we analyzed the 14C-AZA uptake in azi1-1 and dir1. The azi1-1 mutant, but not dir1, showed a significant decrease in uptake compared to wild-type plants. Moreover, in a preliminary radiotracer experiment azi1-1 moved less 14C-AZA from source to sink leaves.Localization studies using confocal microscopy showed AZI1-GFP in cytoplasmic vesicles, plasma membrane/cell wall, in contact sites between ER/chloroplasts and also tightly surround the chloroplasts. Interestingly, the ER contacts sites are proposed as places were lipid exchange occurs. DIR1-GFP localizes mainly in ER and also in vesicles-like structures. Western blot analysis of subcellular fractions was in agreement with confocal localization. Interestingly, co-immunoprecipitation assays using ?HA and ?GFP tagged versions of AZI1 and DIR1 showed interactions between them. In agreement, tissues co-expressing AZI1/DIR1 showed co-localization in ER, vesicles and apoplast.Taken together these results suggest the idea of AZI1/DIR1 LTP-complex acting during SAR-priming probably moving a lipidic signal(s), such as AZA.