Proteomic analysis of rice plasma membrane reveals proteins involved in early defense response to bacterial blight

Plant plasma membrane (PM) proteins play important roles in signal transduction during defense response to an attacking pathogen. By using an improved method of PM protein preparation and PM-bound green fluorescent protein fusion protein as a visible marker, we conducted PM proteomic analysis of the rice suspension cells expressing the disease resistance gene Xa21, to identify PM components involved in the early defense response to bacterial blight (Xanthomonas oryzae pv. oryzae). A total of 20 regulated protein spots were observed on 2-D gels of PM fractions at 12 and 24 h after pathogen inoculation, of which some were differentially regulated between the incompatible and compatible interactions mediated by Xa21, with good correlation between biological repeats. Eleven protein spots with predicted functions in plant defense were identified by MS/MS, including nine putative PM-associated proteins H+-ATPase, protein phosphatase, hypersensitive-induced response protein (OsHIR1), prohibitin (OsPHB2), zinc finger and C2 domain protein, universal stress protein (USP), and heat shock protein. OsHIR1 was modified by the microbal challenge, leading to two differentially accumulated protein spots. Transcript analysis showed that most of the genes were also regulated at transcriptional levels. Our study would provide a starting point for functionality of PM proteins in the rice defense.