Functional Proteomics of Arabidopsis thaliana Guard Cells Uncovers New Stomatal Signaling Pathways

摘要

We isolated a total of 3 3 108 guard cell protoplasts from 22,000 Arabidopsis thaliana plants and identified 1734 uniquenproteins using three complementary proteomic methods: protein spot identification from broad and narrow pH range twodimensionaln(2D) gels, and 2D liquid chromatography–matrix assisted laser desorption/ionization multidimensional proteinnidentification technology. This extensive single-cell-type proteome includes 336 proteins not previously represented inntranscriptome analyses of guard cells and 52 proteins classified as signaling proteins by Gene Ontology analysis, of whichnonly two have been previously assessed in the context of guard cell function. THIOGLUCOSIDE GLUCOHYDROLASE1n(TGG1), a myrosinase that catalyzes the production of toxic isothiocyanates from glucosinolates, showed strikingnabundance in the guard cell proteome. tgg1 mutants were hyposensitive to abscisic acid (ABA) inhibition of guard cellninward K+ channels and stomatal opening, revealing that the glucosinolate-myrosinase system, previously identified as andefense against biotic invaders, is required for key ABA responses of guard cells. Our results also suggest a mechanismnwhereby exposure to abiotic stresses may enhance plant defense against subsequent biotic stressors and exemplify hownenhanced knowledge of the signaling networks of a specific cell type can be gained by proteomics approaches.