Genetic Transformation Of Plant Flowering Gene FT And Its Involvement In Flowering Control

In flowering plants, phase transition from vegetative to reproductive growth is a criticalevent in life cycle. Flowering and seed setting of wheat determines successful cycling ofgenerations, and also affects food security worldwide. A number of major flowering geneshave been cloned in Triticeae species. Wheat vernalization gene VRN3is actally the FloweringLocus T (FT). To characterize molecular bases of flowering control, both transgenicapproaches and mutant analyses were performed in wheat, Brachypodium, and/or barley onFT genes. Transgenic study revealed a positive relationship between levels of FT expressionand flowering/heading time in wheat and Brachypodium. It was shown that FTsilencing/knockdown affected the expression of other flowering gene expression.Characterization of FT gene enables us to easily regulate flowering time and develop wheatcultivars suitable to specific regions and climates. The main results are as follows:1. We idenfied19barley FT members and19Brachypodium FT members. According toprotein sequences, barley and Brachypodium FT genes were divided into four categories:FT-like I, FT-like II, MFT-like, and TFL-like. Among152sequenced plant species, FThomologues were found in12of26monocot species,44of112dicot species, and3of9gymnosperm species, but no FT homologue was detected in4algae species and1bryophytespecies.2. Transgenic wheat and Brachypodium were obtained using particle gun andAgrobacterium-mediated transfer, respectively. Silencing and overexpression of TaFT genedramatically changed the flowering time in wheat, suggesting that TaFT plays crucial role inflowering control. TaFT silencing resulted in non-flowering or late-heading in spring wheat“Bobwhite”; most transgenic plants maintained vegetative growth up to10months andeventually died. Overexpression of TaFT gene in Bobwhite led to extremely early-flowering;many shoots developed reproductive organs during the regeneration process in tissue culture.Transgenic Brachypodium of BdFT genes displayed the same phenotype as discovered inwheat, and silencing of BdFT gene led to non-flowering phenotype. The data proved that FTgenes play a critical role on flowering time control.3. FT silencing/knockdown affected the expression of other flowering genes. Intransgenic wheat, was associated with enhanced expression of GI, CO, and SOC1whichfunctions in FT silencing the photoperiod flowering pathway, while the vernalization gene VRN1were turned down and the repressor genes VRN2and FDL2was turned up. In addition,the flowering time gene FT2was down-regulated in FT silencing plants.4. Mutants were identified during the screening of EMS-based barley population. Fivemutants were obtained for HvVRN1gene, and2of them were nonsense mutation. Six mutantswere found for HvFT gene, and2of them were associated with amino-acid change. However,all five HvFT2mutants had silent mutation.5. FT genes are essential for flowering control. It perceives signals from photoperiod andvernalization pathways, and determines flowering time in wheat. In contrast, VRN1gene is animportant but not essential for flowering time control.