Identification and expression analysis of non-photosynthetic Rubisco small subunit, OsRbcS1-like genes in plants

Rubisco is the key enzyme of photosynthetic CO2 fixation, whereas a Rubisco small subunit homolog (OsRbcS1) in rice, was exclusively expressed in non-photosynthetic organs. In this study, OsRbcS1-like genes were identified in several plant species including foxtail millet (SiRbcS1), tomato (SlRbcS1), Lotus japonicus (LjRbcS1), grape (VvRbcS1A, VvRbcS1B) and Selaginella moellendorffii (SmRbcS1A, SmRbcS1B). RT-PCR analysis revealed that SiRbcS1 was expressed in seeds of foxtail millet. In tomato, SlRbcS1 was expressed in the stamen, pistil and green fruit. In L. japonicus, LjRbcS1 was expressed in the root, nodule and seed. In grape, both VvRbcS1A and VvRbcS1B were expressed in mature leaves and the green berry. In S. moellendorffii, SmRbcS1A and SmRbcS1B displayed similar expression patterns and were expressed in the rhizome and root. Although these OsRbcS1-like genes were expressed in photosynthetic organs in S. moellendorffii, its expression levels were higher in non-photosynthetic organs than in photosynthetic organs. These results suggest that OsRbcS1-like RbcS functions in metabolic pathways other than photosynthetic CO2 fixation in various organs.