Development of protein biomarkers for the authentication of organic rice

The rice protein profiles of Oryza sativa L (Koshihikari) grown under organic and conventional cultivation regimes were compared on 2-D gels to develop diagnostic marker proteins for organic rice. The selected proteins, differentially expressed between organic and conventional rice, were compared with the differentially expressed proteins of another organic and conventional rice pairing, produced at a different location. In the first comparison among conventional, no-chemical, and organic rice grown in the same region, Korea, 13 proteins exhibiting differential expression in organic and conventionally grown plants were selected. Eight of the 13 proteins were down-regulated, and the 5 remaining proteins were up-regulated from conventional to organic rice. The second comparison pairing from Kyungju, revealed 12 differentially expressed proteins, with 8 down-regulated and 4 up-regulated proteins. Ten of the differentially expressed proteins that overlapped between the two comparison sets could not be clustered into any functional group using a functional annotation clustering tool. Further comparisons using another set of conventional and organic rice, belonging to a different variety of Oryza sativa L and produced in Sanchung, revealed 8 differentially expressed proteins, 5 of which were down-regulated and 3 of which were upregulated in the organic rice. Overall, 3 differentially expressed proteins were commonly found in all three organic rice crops. These 3 proteins, along with other overlapping differentially expressed proteins, can provide a good starting point for the development of signature proteins that can be used for the authentication of organic rice with a follow-up studies with more comparison sets.