Floral initiation is regulated by an elaborate network of signalling pathways, including the photoperiodic pathway. In Arabidopsis, flowering is promoted through this pathway by activation of FLOWERING LOCUS T (FT) by CONSTANS (CO) in long days. During juvenility plants are incapable of flowering in response to environmental conditions that would normally be favourable. This project studies the molecular basis of floral incompetence during juvenility in the model annual species, Antirrhinum majus and the important commercial tree species, Olea europaea, which has an extended juvenile phase. Photoperiod transfer experiments were used to measure the length of juvenility in plants grown in controlled environment cabinets at different Daily Light Integrals. Analysis of Antirrhinum FT (AmFT) expression during development showed that AmFT expression is minimal during juvenility and increases in all leaves following the end of the juvenile phase. The photoperiodic pathway was shown to be active during juvenility, suggesting that an additional mechanism involving the repression of FT could be involved in the regulation of juvenility. Full length Antirrhinum and Olive cDNAs representing homologues of the Arabidopsis FT repressors TEMPRANILLO 1 (AtTEM1) and AtTEM2, which act antagonistically with CO, were isolated. Molecular and phylogenetic analyses revealed high amino acid identities between Antirrhinum (AmTEM) and Olive (OeTEM) TEM-like proteins and AtTEM1 & 2. AmTEM and OeTEM proteins contain AP2 and B3 domains, consistent with AtTEM1 and AtTEM2, and can be classified as Class I members of the RAV sub-family of B3 transcription factors. AmTEM and OeTEM expression levels were shown to be higher during juvenility suggesting a potential role for TEM in controlling juvenility. A reciprocal relationship between expression levels of AmTEM/AtTEM1 and AmFT/AtFT was revealed in both Antirrhinum and Arabidopsis. Analysis of expression across development showed that AmTEM/AtTEM1 levels decline at around the time juvenility ends corresponding to when AmFT/AtFT levels start to increase. Arabidopsis tem1 mutants over-expressing AmTEM, OeTEM or AtTEM1 exhibited delayed flowering compared to the tem1 mutant, which demonstrated their role in regulating flowering time. Over-expression of AmTEM was shown to increase the length of the juvenile phase, delay the induction of AtCO and AtFT expression and reduce the overall levels of AtFT expression. Conversely, the juvenile phases of tem1 single and tem1/2 double mutants were shown to be shorter than in wild-type plants, with the induction of AtCO and AtFT expression occurring earlier. These findings are consistent with a role for TEM in regulating juvenility, which occurs through the down-regulation of FT and CO, and results in the inability to proceed to reproductive growth.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:560324 |
| Date | January 2012 |
| Creators | Sgamma, Tiziana |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/48973/ |
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