Grain number is an important factor in determining grain production of rice ( Oryza

41 Grain number is an important factor in determining grain production of rice (Oryza 42 sativa L.). The molecular genetic basis for grain number is complex. Discovering 43 new genes involved in regulating rice grain number increases our knowledge 44 regarding its molecular mechanisms and aids breeding programs. Here, we 45 identified GRAINS NUMBER 2 (GN2), a novel gene that is responsible for rice grain 46 number, from ‘Yuanjiang’ common wild rice (Oryza rufipogon Griff.). Transgenic 47 plants over-expressing GN2 showed less grain number, reduced plant height, and 48 later heading date than control plants. Interestingly, GN2 arose through the 49 insertion of a 1,094-bp sequence from LOC_Os02g45150 into the third exon of 50 LOC_Os02g56630, and the inserted sequence recruited its nearby sequence to 51 generate the chimeric GN2. The gene structure and expression pattern of GN2 were 52 distinct from those of LOC_Os02g45150 and LOC_Os02g56630. A sequence analysis 53 showed that GN2 may be generated in the natural population of ‘Yuanjiang’ 54 common wild rice. In this study, we identified a novel functional chimeric gene and 55 also provided information regarding the molecular mechanisms regulating rice 56 grain number. 57