Phosphoproteomic profiling of microsomal fractions in leaves of Cogon grass (Imperata cylindrica)

Abstract

Cogon grass [Imperata cylindrica (L.) Beauv. var. major] is one of the top-ten weeds. It is a widespread distributed C4 plant. In particular, one ecotype (Chuwei) is salt and flooding tolerant. Imperata leaves harvested from Chuwei and Sarlun control site were subjected to microsomal fractionation followed by membrane shaving using trypsin. The resulting peptides were further enriched by columns and mass spectrometry analyses for phosphopeptide identification. The phosphoproteomic analysis identified 20 phosphorylation sites from 16 unique phosphorylated peptides in the microsomal fractions isolated from leaves of Imperata, of which 5 are specific to Chuwei ecotype. Out of these 5 phosphopeptides, 2 belong to sugar transporters, including a sucrose transporter SUT1 which appears to be a novel and C4-specific phosphorylation site. Whereas the other 3 belong to photosynthesis proteins of which 2 are C4 enzymes. Interestingly, two independent phosphopeptides of tonoplast monosaccharide transporter 2 (TMT2) were identified in Chuwei ecotype and the other salt-intolerant Sarlun population individually. Our phosphoproteomic study identified differentially phosphorylated peptides of membrane proteins which may play an important role in the salt stress response of Imperata.