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植物开花时间控制的分子机理 Molecular mechanism of plant flowering time control

第十章 基因和发育 第二讲. 植物开花时间控制的分子机理 Molecular mechanism of plant flowering time control. By Hongwei Guo, Peking University, 2008.12.18. Transition to reproduction. When to flower is a matter of the survival of species. ?. Vegetative phase. Reproductive phase.

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植物开花时间控制的分子机理 Molecular mechanism of plant flowering time control

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  1. 第十章 基因和发育 第二讲 植物开花时间控制的分子机理 Molecular mechanism of plant flowering time control By Hongwei Guo, Peking University, 2008.12.18

  2. Transition to reproduction When to flower is a matter of the survival of species ? Vegetative phase Reproductive phase

  3. Two major pathways regulating floral transition Photoperiodic flowering (光周期开花): day-length dependent flowering time control Vernalization (春化): cold-promoted flowering

  4. (“Maryland Mammoth” cultivar of tobacco)

  5. Floral induction of leaves of Short Day plant Perrila crispa “Something” must be produced in leaves and “move” to the meristem Long journey to identify “Florigen” began (Lang and Zeevart)

  6. Multiple grafting experiment with Perilla Long distance transport---- thru vascular tissue

  7. The flowering signal: florigen vegetative or reproductive growth? • the flowering signal is generated in the leaf • the signal goes one way: from the leaf to the apex • Grafting transmittable SAM Florigen Florigen Florigen

  8. Photoperiodic flowering • Two essential questions: • 1. How does the leaf measure day-length? • 2. What is the florigen?

  9. Genetics provides the answers Arabidopsis: Long Day Plant Flowering is induced by Long Day (LD) Certain late flowering mutants are blind to photoperiod cryptochrome 2 (cry2) phytochrome A (phyA) contstans (co) flowering locus t (ft) Cry2: blue light receptor PhyA: Far-red light receptor CO: transcriptional co-activator FT: transcriptional co-activator (?)

  10. 3 wavelengths (Blue, Red, Far-red) are important in regulating plant growth and development

  11. Phytochromes (光敏色素）：Red/Far-redlight receptors Cryptochromes (隐花色素）：Blue light receptors phyA also absorbs blue light

  12. Signal Trans-duction

  13. (originally proposed by Boenning, 1936) Light has a dual role in this model: - entrains the circadian oscillation of light- and dark-sensitive phases - directly required for the production of the signal.

  14. PRR: photoperiod response regulator

  15. PRR: photoperiod response regulator

  16. CO is essential for photoperiodic flowering, as co mutant is late flowering and almost a day-neutral plant. It encodes a transcriptional regulator.

  17. （春化） LFY A, B, C, E class genes Is co the PRR that measures daylength?

  18. COisrequiredforFTexpression

  19. FT mRNA levels determine flowering time LD: early flowering SD: late flowering phyBDE: early flowering cry2: late flowering

  20. Cry inhibits CO protein degradation in light When CO mRNA peaks at midnight in SDs, COP1 is predominantly localized in the nucleus. CRY interacts with COP1 but is not able to repress its activity. COP1–CO interaction results in ubiquitination and degradation of CO (A), whereas when CO mRNA peaks in the afternoon in LDs, light activation of CRY during the daytime might mediate translocation of COP1 from nucleus to cytoplasm. Consequently, CO is able to accumulate and activate the transcription of FT to promote flowering (B). U, ubiquitin.

  21. Molecular mechanism of photoperiodic flowering

  22. Photoperiod-dependent activation of COproteinand FT mRNA CDF1: circadian dependent factor CO protein measures day-length FT mRNA level determines flowering time CO mRNA is regulated by circadian clock. CO protein is stabilized by light Therefore, FT expression is activated only in long day

  23. FT (or Hd3a) is a floral activator both in LD and SD plants Long Day Plant Short Day Plant (Kobayashi & Weigel, 2007) CO in Long Day plants and similar proteins (Hd1) in Short Day plants are regulated in opposite ways

  24. 2005 retr

  25. Heating the leaf of pHSP::FT transgenic plants can promote flowering, and FT mRNA can be detected in SAM

  26. However, the mRNA hypothesis was challengedin 2006 by a PNASpaper, the original Sciencepaper was retracted in 2007. 5 more papers have been published in 2007 – allargued that FT protein is the florigen, in at least 5different plant species: Arabidopsis, rice, tomato,tobacco, pumpkin. Yuval Eshed‘s labin Israel clonedtomato FT genefrom a tomatomutant, sft.TheyoverexpressedSFT in tomato,resulting in earlyflowering, but theyfound littletransgenic SFTmRNA in the apicalmeristem。

  27. leaves SAM

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