OsPLB gene expressed during seed germination encodes a phospholipase in rice

Hydrolysis of phospholipid monolayer by phospholipases is an important event in the mobilization of stored lipids for seed germination. However, the identification and functional characterization of cereal phospholipases, especially during rice germination, are limited. In the present study, we have identified and characterized a phospholipase OsPLB gene expressed during germination. The full-length coding region of OsPLB was cloned into pRSETA as well as pYES2/NTC vector. The recombinant protein was successfully expressed in both E. coli and Saccharomyces cerevisiae. The recombinant protein was purified to homogeneity by affinity chromatography, and it was further confirmed by MS/MS analysis. In vitro lipase assay and lipidome analysis using high-resolution mass spectrometry showed phosphatidylcholine (PC) specific phospholipase B activity. The results revealed that protein encoded by OsPLB gene prefers to hydrolyze PCs with C28, C32, and C34 containing unsaturated fatty acids. Collectively, the present study describes the identification and characterization of a phospholipase B, which hydrolyze PC, a major component of phospholipid monolayer covering storage lipid, as an initial event during rice seed germination.