Secretion of Phospholipase Dδ Functions as a Regulatory Mechanism in Plant Innate Immunity

Abstract

Plant phospholipase Ds (PLDs), essential regulators of phospholipid signaling, function in multiple signal transduction cascades; however, the mechanisms regulating PLDs in response to pathogens remain unclear. Here, we found that Arabidopsis (Arabidopsis thaliana) PLDd accumulated in cells at the entry sites of the barley powdery mildew fungus, Blumeria graminis f. sp hordei. Using fluorescence recovery after photobleaching and single-molecule analysis, we observed higher PLDd density in the plasma membrane after chitin treatment; PLDd also underwent rapid exocytosis. Fluorescence resonance energy transfer with fluorescence lifetime imaging microscopy showed that the interaction between PLDd and the microdomain marker AtREMORIN1.3 (AtREM1.3) increased in response to chitin, indicating that exocytosis facilitates rapid, efficient sorting of PLDd into microdomains upon pathogen stimulus. We further unveiled a trade-off between brefeldin A (BFA)-resistant and-sensitive pathways in secretion of PLDd under diverse conditions. Upon pathogen attack, PLDd secretion involved syntaxin-associated VAMP721/722-mediated exocytosis sensitive to BFA. Analysis of phosphatidic acid (PA), hydrogen peroxide, and jasmonic acid (JA) levels and expression of related genes indicated that the relocalization of PLDd is crucial for its activation to produce PA and initiate reactive oxygen species and JA signaling pathways. Together, our findings revealed that the translocation of PLDd to papillae is modulated by exocytosis, thus triggering PA-mediated signaling in plant innate immunity.

Systemin‐mediated long‐distance systemic defense responses

“…Additionally, Pro‐SYS does not contain prenylation sites, N‐linked glycosylation sites, or transmembrane domains, suggesting that it is biosynthesized, stored, and processed in the cytoplasm and exported into the extracellular space via a noncanonical pathway (Dombrowski et al , 1999; Xing et al . , 2019). Indeed, immunochemical analyses have demonstrated that Pro‐SYS is located in the cytosol of vascular parenchyma cells in wounded tissues (Narváez‐Vásquez & Ryan, 2004).…”

Lipid Rafts to the Rescue! Plants under Fungal Attack Recruit Phospholipase Dδ

“…Green, PLDd-GFP; magenta, propidium iodide-stained powdery mildew; arrowheads, attempted fungal penetration sites; DMSO, dimethylsulfoxide; BFA, brefeldin A; scale bars = 20 mm. (Adapted from Xing et al [2019], Figures 4N and 4O). [OPEN] Articles can be viewed without a subscription.…”

“…But how does this structure form, and what regulates its formation? A recent study by Xing et al (2019) provides key insights into these questions. Previous studies have shown that phosphatidic acid (PA) serves as a signaling lipid that promotes plant immune responses and that phospholipase D enzymes (PLDs), which hydrolyze structural phospholipids, generate PA (for a review, see Zhao, 2015).…”

“…Previous studies have shown that phosphatidic acid (PA) serves as a signaling lipid that promotes plant immune responses and that phospholipase D enzymes (PLDs), which hydrolyze structural phospholipids, generate PA (for a review, see Zhao, 2015). Xing et al (2019) found that the PM localization of PLDd tagged with green fluorescent protein (PLDd-GFP) showed strong accumulation at the papillae where Bgh had attempted penetration (see figure) and also increased in abundance throughout the PM when treated with chitin, a fungal elicitor of pathogen-associated molecular pattern-triggered immunity in plants. Coexpression analysis together with Fö rster resonance energy transfer-fluorescence lifetime imaging microscopy of PLDd-GFP and AtREMOR-IN1.3-mCherry suggested that PLDd-GFP localizes to sterol-rich microdomains (or lipid rafts) of papillae and that PLDd accumulation increases in response to chitin treatment.…”

“…DOI 10.1105/tpc.19.00822 ; originally published onlineOctober 22, 2019;2019;31;2819-2820 This information is current as of July 3, 2020…”