Mutation in the Non‐coding Sequence of Badh2 Gene Reduces its Transcription and Translation in Fragrant Rice ‘Nankai 138’

It has been previously demonstrated that loss‐of‐function mutations in the coding sequence of the betaine aldehyde dehydrogenase 2 (BADH2) gene result in the accumulation of 2‐acetyl‐1‐pyrroline (2‐AP), the key component of fragrance in most rice cultivars. In this work, a novel allele of the BADH2 gene, badh2‐p‐5′UTR , found in a new fragrant rice cultivar Nankai 138 was studied. In Nankai 138, mutations in the non‐coding sequence of the BADH2 gene result in downregulation of the mRNA. This makes the specific activity of the BADH2 protein in the Nankai 138 decline from 50 to 40% of the value observed in Nipponbare from 12 to 20 d after flowering, and subsequently leading an increase of 2‐AP content to 47.8 ng g –1 in brown rice. In conclusion, the mutations in non‐coding region of BADH2 gene in Nankai 138 weaken transcription of the gene thereby reducing the accumulation of the functional protein and conferring fragrance to rice. These results add to the current knowledge of molecular mechanism of fragrance in rice.