Stomatal openings are a major route of pathogen entry into the plant, and plants have evolved mechanisms to regulate stomatal aperture as innate immune response against bacterial invasion. However, the mechanisms underlying stomatal immunity are not fully understood.
Taking advantage of high-throughput liquid chromatography tandem mass spectrometry (LC-MS/MS) and a TiO2/ZrO2-based phosphopeptide enrichment protocol, we performed a label-free proteomic and phosphoproteomic analyses of enriched guard cells in response to a model bacterial pathogen Pseudomonas syringae pv. tomato DC3000 .
In total, 495 proteins and 1229 phosphoproteins were identified as differentially regulated. These proteins are involved in a variety of signaling pathways, e.g., hormone and reactive oxygen species signaling. The pathways form interactive molecular networks that regulate stomatal immunity. Based on the motifs of the phosphoproteins, we tentatively identified different protein kinases responsible for the phosphorylation activities.
This study is the first comprehensive investigation of the guard cell phosphoproteome, and has provided new insights into the multifaceted mechanisms of stomatal immunity. The differential phospohoproteins are potential targets for engineering or breeding for enhancing plant defense