Synthetic control of flowering in rice independent of the cultivation environment.

For genetically homogeneous crops, the timing of flowering is determined largely by the cultivation environment and is strongly associated with the yield and quality of the harvest. Flowering time and other agronomical traits are often tightly correlated, which can lead to difficulty excluding the effects of flowering time when evaluating the characteristics of different genetic varieties. Here, we describe the development of transgenic rice plants whose flowering time can be controlled by specific agrochemicals. We first developed non-flowering rice plants by overexpressing a floral repressor gene, Grain number, plant height and heading date 7 (Ghd7), to inhibit any environmentally induced spontaneous flowering. We then co-transformed plants with a rice florigen gene, Heading date 3a (Hd3a), which is induced by the application of specific agrochemicals. This permitted the flowering time to be experimentally controlled regardless of the cultivation environment: some transgenic plants flowered only after agrochemical treatment. Furthermore, plant size and yield-related traits could, in some cases, be increased owing to both a longer duration of vegetative growth and an increased panicle size. This ability to control flowering time experimentally, independently of environmental variables, may lead to production of crops suitable for growth in different climates and facilitate breeding for various agronomical traits.