Proteomics to identify pathogenesis-related proteins in rice roots under water deficit

Upland and lowland rice (Oryza sativa L.) showed different mechanisms of water stress resistance. Hydroponically grown 3-week-old seedlings of a lowland variety IR64 and an upland variety were exposed to 15% polyethylene glycol (PEG-6000). After 7 d of treatment, IR64 maintained high relative water content and developed a well-branched root. Therefore, IR64 had better water-deficit tolerance than Azucena under PEG treatment. To identify water-deficit-responsive proteins associated with the tolerance differences between two ecotypes, a comparative proteomic analysis of roots was conducted. Out of 700 proteins reproducibly detected on two-dimensional electrophoresis gels, 65 proteins exhibited significant changes in at least one ecotype at 48 h of water deficit. Only 15 proteins showed different responses to water deficit between the two ecotypes. Twelve proteins were identified by matrix-assisted laser desorption/ionization-time of flight/time of flight-mass spectrometry, which involved in energy and metabolism, protein processing and degradation, detoxification and pathogenrelated (PR) proteins, i.e. PR-1a, RSOsPR10 and JIOsPR10. All three PR proteins were induced more strongly in IR64 than in Azucena by water deficit at both protein and mRNA level. The results suggested that PR-1a, RSOsPR10 and JIOsPR10 may play important roles in protecting root cells against water deficit in rice.