The serine proteinase inhibitor OsSerpin is a potent tillering regulator in rice

Tillering in rice (Oryza sativa L.) is an important agronomic trait that enhances grain production. A tiller is a specialized grain-bearing branch that is formed on a non-elongated basal internode that grows independently of the mother stem. Transgenic rice over-expressing the transcription factor OsTB1, a homologue of maize TB1 (Teosinte Branched 1), exhibits markedly reduced lateral branching without the propagation of axillary buds being affected. However, the tillering mechanism remains unknown. Therefore, to further understand that mechanism, we applied proteomics methodology to isolate the proteins involved. Using two-dimensional gel electrophoresis and mass spectrometry, our analysis of the basal nodes from two rice cultivars that differ in their numbers of tillers showed that a rice serine proteinase inhibitor, OsSerpin, accumulates in great amounts in high-tillering 'Hwachung' rice. Northern blot analysis revealed that much more OsSerpin transcript is found in 'Hwachung' than in relatively low-tillering 'Hanmaeum', likely because of high levels of transcription. Therefore, our data suggest that OsSerpin content determines the extent of lateral branching.