Investigating long-distance signal movement during Systemic Acquired Resistance in Arabidopsis
P. CARELLA (1), J. Merl-Pham (2), D. Wilson (1), S. Dey (3), S. Hauck (2), A. Vlot (3), R. Cameron (1) (1) Department of Biology, McMaster University, Canada; (2) Helmholtz Zentrum Muenchen, Research Unit Protein Science, Germany; (3) Helmholtz Zentrum Muenchen, Institute of Biochemical Plant Pathology, Germany

During Systemic Acquired Resistance (SAR), a SAR-inducing infection in one leaf initiates movement of phloem-mobile signals to uninfected distant leaves to prime plants for enhanced resistance to future infections. We previously demonstrated that the lipid transfer protein DIR1moves to distant leaves via the phloem to activate SAR using an estrogen inducible Es:DIR1-GFP/dir1-1 plant line. To discover how DIR1 gains access to the phloem we made use of plant lines with compromised plasmodesmatal cell-to-cell movement caused by overexpression of Plasmodesmata-Located Proteins. These lines were defective for SAR and DIR1 was not observed in distant leaf phloem exudates, supporting the idea that cell-to-cell movement of DIR1 through plasmodesmata is important for long-distance SAR signaling. Given that protein levels rise in phloem exudates after SAR induction, we speculate that phloem proteins besides DIR1 also contribute to long-distance signal movement in the phloem. To identify SAR-specific phloem proteins, we compared phloem exudate proteomes collected from mock- and SAR-induced leaves using quantitative LC-MS/MS. Numerous proteins were differentially abundant in SAR-induced versus mock-induced phloem exudates. T-DNA knock-out lines in some of these genes including m-type thioredoxins, a major latex protein-like protein and the UVR8 photoreceptor, were negatively impacted in SAR, indicating that these proteins contribute to the SAR response. The Arabidopsis SAR phloem proteome adds to our limited knowledge of protein composition in the phloem and is a valuable resource for understanding SAR long-distance signaling and the dynamic nature of the phloem during plant-pathogen interactions.

Abstract Number: P18-661
Session Type: Poster