Fragrance of the rice grain achieved via artificial microRNA-induced down-regulation of OsBADH2

With 6 figures and 1 table Abstract 2-acetyl-1-pyrroline (2AP) is the principal compound responsible for grain fragrance in rice. In fragrant rice cultivars, BADH2 (betaine-aldehyde dehydrogenase 2) is inactivated. Here, we describe the effect of amiRNA (artificial microRNA) transgenesis targeted at BADH2 in rice. BADH2 (but not BADH1) expression was down-regulated in transgenic lines where the amiRNA was driven by the maize ubiquitin promoter, and in these lines, grain 2AP content was also significantly elevated; meanwhile, 2AP could not be detected in the grain of wild-type lines. The leaf proline content in the transgenics was increased through the simultaneous down-regulation of PRODH and up-regulation of P5CS. In transgenic lines where the same amiRNA was driven by the endosperm-specific promoter GluC, no effect on BADH2 expression was detectable, and the content of grain 2AP did not differ from that present in wild-type grains.