Arabidopsis AZI1-family of lipid transfer proteins mediate priming-signal(s) mobilization for systemic defense programs. / Conferencista invitado

CECCHINI NM; STEFFES K; SCHLÄPPI MR; GIFFORD AN; GREENBERG JT

Conferencia; Gordon Research Conferences, Plant Lipids: Structure, Metabolism & Function.; 2015

Priming is a major mechanism behind the immunological ?memory? observed during two key plant systemic defenses against microorganisms: systemic acquired resistance (SAR) and induced systemic resistance (ISR). A lipidic signal, azelaic acid (AZA), was identified as a chloroplast lipid-derived mobile priming factor. Here we show that the lipid transfer protein (LTP)-like AZI1 and its closest paralog EARLI1 are necessary for SAR, ISR and the systemic movement and uptake of AZA in Arabidopsis. Localization and fractionation studies indicate that AZI1 and EARLI1 localize to expected places for lipid exchange/movement to occur: vesicles-like structures, the ER/plasmodesmata, plasma membrane, and chloroplasts outer envelope, enriched in contact sites between ER/chloroplasts. After SAR triggering infection, the fraction of AZI1 associated with chloroplasts increases, suggesting a key role for the chloroplast pool of these proteins. Moreover, these LTP-like proteins form complexes with each other and with an unrelated LTP, DIR1, and act at the site of SAR induction. The results suggest the existence of a LTPs complex(s) working in different steps/places during SAR/ISR establishment, probably allowing movement of a lipidic signal(s), such as AZA, intracellularly as well as over long distance to the systemic tissues. Furthermore, AZI1, EARLI1 and other AZI1-paralogs protein architecture and requirements for their subcellular localization patterns and dynamic trafficking indicate they use a novel mode of plastid targeting.