| The regulation of flowering has been investigated in numerous herbaceous species. However, information on the molecular mechanisms necessary for phase transition and flower initiation in perennial tree crops is still limited. Homologues of TERMINAL FLOWER, LEAFY, and APETALA1 were isolated from 'Washington' navel orange ( Citrus sinensis L. Osbeck) and assessed for sequence and structural similarities with their respective counterparts in Arabidopsis thaliana . The deduced protein sequences of CsTFL, CsLFY, and CsAP1 had 74%, 68%, and 66% identity, respectively, with the Arabidopsis homologues. Using the 35S cauliflower mosaic virus (35S CaMV) promoter, CsTFL, CsLFY, and CsAP1 were overexpressed in Arabidopsis wild type Columbia and tfl1--2, lfy-10, and ap1--3 mutant plants. Transgenic wild type plants constitutively expressing the CsTFL, CsLFY, and CsAP1 transgene produced phenotypes similar to those observed for transgenic plants constitutively expressing the homologous Arabidopsis gene. The severity of the phenotype was correlated with the amount of CsTFL, CsLFY, and CsAP1 transcript that accumulated. Partial or full complementation of phenotype was related to the accumulation of CsTFL, CsLFY, and CsAP1 transcripts in their respective mutant.;To investigate the regulation of CsTFL, CsLFY, and CsAP1, mature (florally competent) and juvenile (florally-incompetent) 'Washington' navel orange plants were placed under low-temperature floral-inductive conditions and transcript accumulation was measured and compared. There were distinct differences in transcript accumulation between mature and juvenile plants. Overall, more CsTFL transcript accumulated in juvenile plants compared to mature plants. In contrast, CsLFY and CsAP1 accumulated to higher levels in mature plants. Taken together, the results of this study provide evidence that the C. sinensis floral regulatory genes isolated in this study have high amino acid conservation and functional equivalency to their Arabidopsis homologues. In addition, the differences in the regulation of these genes between mature and juvenile citrus plants highlights the distinctiveness of these two developmental phases and suggests that manipulation of CsTFL versus CsLFY or CsAP1 these genes could impact phase transition in citrus. |
