Identification of elicitor-responsive proteins in rice leaves by a proteomic approach

Experiments were conducted to identify the differentially expressed proteins in rice (Oryza sativa L.) plants after treatment with the glycoprotein elicitor CSB I, purified from ZC(13), a race of the rice blast fungus Magnaporthe grisea. The interactions of two near isogenic lines of rice, C101A51 and CO39, with ZC(13) resulted in completely incompatible and compatible types, respectively. Proteins were extracted from rice leaves at 12 and 24 h after treatment with CSB I. Temporal changes in total proteins were examined using 2-DE. Among more than 900 protein spots reproducibly detected on each gel, 11 were up-regulated, three were down-regulated and seven were newly induced during, at a minimum, one time point. Twenty-one differentially expressed proteins were identified by linear ion trap quadrupole (LTQ)-MS/MS. The identified proteins were classified into six categories based on their putative function reported: (i) defense proteins (PR-10a, PR-5 and putative salt-induced protein), (ii) signal transduction (nucleoside diphosphate kinase and putative profilin), (iii) ROS (Mn-SOD, Cu/Zn-SOD, GST and CAT), (iv) programmed cell death (translationally controlled tumor protein), (v) molecule biosynthesis (putative ribosomal protein S5, putative ribosomal protein L12, putative translational elongation factor Tu and putative chaperonin 21 precursor) and (vi) metabolism (putative fructose-bisphosphate aldolase class-I, putative malate dehydrogenase, cytoplasmic malate dehydrogenase, putative acid phosphatase, putative transketolase1 and gamma hydroxybutyrate dehydrogenase-like protein). All of these proteins (except Cu/Zn-SOD, putative acid phosphatase and translationally controlled tumor protein) were induced faster and to a higher degree in C101A51 than in CO39. These data suggest that the incompatible rice line may possess a more sensitive recognition system that can identify and react to specific chemical, biological or physical triggers in a more efficient manner, thus eliciting an early and fast defense response.