【课件】高级植物生理学课件第七章植物的生殖生理

1、Plant ReproductionZichao Mao Life cycle of plant Transition to reproductionFlower organ developmentGametogenesis and fertilizationPlant ReproductionTransition to reproductionVegetative phaseReproductive phase?InflorescenceFlowerProduction of flowers involves two transitions in ArabidopsisSC: stem ce

2、llP: organ primordiaSe: sepalConvert SAM （Shoot Apical Meristem)to inflorescence meristem (infinite, making lateral organs)2. Convert inflorescence meristem to floral meristem (terminal, flowers)Factors regulating the transitionsVegetative meristemInflorescence meristemFloral meristemGenes (flowerin

3、g-time genes and floral identity genes)Light (photoperiod)The biological clockTemperature Hormones affecting the transition of vegetative growth to reproductive growthWTemf2Flowering-time genesemf1embryonic floweraffecting formation of inflorescence and floral meristemsFloral identity genesInfloresc

4、ence (from Inflorescence meristem)Flower (from Floral meristem)terminal flower 1 (tfl1): Convert the inflorescence meristem to the flower meristem. leafy (lfy): produce more inflorescences, delayed floweringMutations in floral identity genestfl1FUNCTION Controls inflorescence meristem identity and i

5、s required for maintenance of a indeterminate inflorescence. Prevents the expression of APETALA1 and LEAFY. Also plays a role in the regulation of the time of flowering in the long-day flowering pathway. May form plexes with phosphorylated ligands by interfering with kinases and their effectors Expr

6、essed below the apical dome of inflorescence and coflorescence meristems, and in inflorescence stem. Weakly expressed in vegetative phase from day 2 or day 3. Increased expression after mitment to flowering from day 7 on. LEAFY;LFY, FUNCTIONS IN: chromatin DNA binding, transcription factor activity,

7、 sequence-specific DNA binding; INVOLVED IN: flower development, maintenance of inflorescence meristem identity, response to gibberellin stimulus, gibberellic acid mediated signaling; LOCATED IN: nucleus; EXPRESSED IN: shoot apex, leaf whorl, embryo, flower, seed; EXPRESSED DURING: 7 growth stages;

8、Factors regulating the transition to reproductionVegetative meristemInflorescence meristemFloral meristemEMFTF1LFYGarner and Allard (1920s)The discovery of photoperiodismSoybeans (Glycine max) planted over a three-month period all flowered about the same timeMany more experiments were followed: Elim

9、inate a variety of environmental conditions: Nutrition, temperature, and light intensityRelative length of day and night decides the flowering timePhotoperiodism: ability of an organism to measure the proportion of daylight during a 24-hour period Varies according to the latitude and seasonal change

10、s. PhotoperiodCritical daylengthCriticalDaylength(CD)Xanthium(苍耳）: a short day plant, flowers when CD is LESS than 15.5 hours. Hyoscyamus(茛菪 ): a long day plant, flowers when CD is MORE than 11 hours.Plants are induced to flower by different photoperiodsshort day (SD) : plants are stimulated to flow

11、er when the length of day falls below a thresholdlong day (LD): plants are stimulated to flower when the length of day exceeds a thresholdDay neutral (DN): plants flower indifference to the changes of day length. Long-short-day: flowering requires certain number of short days are preceded by a certa

12、in number of long days.Short-long-day: flowering requires certain number of long days are preceded by a certain number of short days.Intermediate-daylength: not flowering if the daylength is too short or too long. Plants that respond to lengthening days and flower in the spring or early summer are k

13、nown as long-day (LD) plants. Short-day (SD) plants flower in the late summer or autumn in response to shortening days and lengthening nights Do plants really measure the length of the daylength? Xanthium flowers when the dark period exceeds 8.5 hours. Hamner and Bonner (1938): Xanthium strumarium(苍

14、耳）, a SD plant with CD = 15.5 hoursShort interruption of dark period, even by a pulse of light as short as 1 minute delays flowering.The relative length of dark is not the determining factor.Similar results were obtained with other SD plants.For LD plantsA longer dark period inhibits flowering.Light

15、 break induces flowering.What tissues/organs perceive photoperiod?Exp. 1: The leaf or apex of Perilla（紫苏 ） (a short day plant) was exposed to different daylength. Exp. 2: Grafting experiment with Perillathe flowering signal is generated in the leafthe signal goes one way: from the leaf to the apexGr

16、afting transmittableThe flowering signal: florigen ?vegetative or reproductive growth?SAMFlorigenFlorigenFlorigen Recent studies in Arabidopsis and rice have made a strong case that florigen, or at least aponent of the floral stimulus, is the floral integrator FT. The FT gene is expressed in leaves,

17、 and the protein travels to the meristem where it interacts with another integrator, FD, to initiate the floral transition FT-like genes ( FD, FVE, FCA, FY, and FPA) are ubiquitous in plants and have been found to regulate flowering in a variety of species including wheat and poplarThe role of phyto

18、chrome in de-etiolation responsePhytochrome: a molecular switching mechanismThe effect of light on the biological clockPhytoperiodism and control of floweringShort-day plant: required a light period shorter than a critical length to flowerlong-day plant: required a light period longer than a critica

19、l length to flowerDay-neutral plant: unaffected by photoperiod and flower when reaching a certain stage of maturityVernalization: use of pretreatment with cold to induce floweringThe Arabidopsis biological clockThe central oscillator: CCA1, LHY, and TOC1 (these are transcription factors) and other p

20、roteins33Present in plants, animals, fungi, and some photosynthetic bacteriaAn internal time measuring system (“clock”) that runs on its own with a periodicity of nearly 24 hours. It can be “reset” by external signals. The biological clockTemperatureBiological clocks andcircadian rhythmsThe Arabidop

21、sis biological clock CCA1 and LHY are expressed during the day and together repress expression of TOC1 during the dayTOC1 is expressed at night and is required for activation of CCA1 and LHY1, beginning just before morningLack of the nyctinastic movement: diurnal rise and fall of leavesAltered flowe

22、ring time in some mutantscca1: early floweringlhy: early floweringtoc1: early floweringSome other clock mutants can be late flowering Mutations in the clock genesTemperature: VernalizationVernalization: low temperature treatment can promote flowering in some plants. The vernalization-effective tempe

23、rature and duration of low temperature treatment may vary. Vernalization is perceived by the shoot apex.The vernalization state is grafting transmissible.Definition the acquisition or acceleration of the ability to flower by a chilling treatmentPlants have evolved many systems to sense their environ

24、ment and to modify their growth and development accordingly. One example is vernalization, the process by which flowering is promoted as plants sense exposure to the cold temperatures of winter. A requirement for vernalization is an adaptive trait that helps prevent flowering before winter and permi

25、ts flowering in the favorable conditions of spring. In Arabidopsis and cereals, vernalization results in the suppression of genes that repress flowering. We describe recent progress in understanding the molecular basis of this suppression. In Arabidopsis, vernalization involves the recruitment of ch

26、romatin-modifying plexes to a clade of flowering repressors that are silenced epigenetically via histone modifications. vernalizationCan be induced quicklyIncreases plant resistance to freezing stressDoes not affect flowering time. Cold acclimationVenalization in cerealsMachanism of Vernalization Ve

27、rnalization-mediated changes in FLC chromatin. (a) Prior to cold exposure, FLC is actively expressed. The plexes that maintain this active chromatin conformation include the PAF plex, which methylates histone 3 tails at lysine 4 and 36 (H3K4triMe and H3K36triMe), a SWR1-like plex, which deposits a h

28、istone 2A variant in the nucleosomes of FLC chromatin, and H2B ubiquitinases like HUB1 and HUB2 that ubiquitinate histone 2B tails (H2Bub1). Although FLC is in an active state, there are repressive plexes present such as Polyb Repression Complex 2 and some degree of lysine 27 methylation of histone

29、3 (H3K27triMea repressive modification) (b) During cold exposure, FLC repression is initiated. VIN3 is induced, VIN3 and VIL1/VRN5 associate with the Polyb plex, the density of repressive chromatin modifications such as lysine 27 methylation of histone 3 increases, and repressors such as LIKE HETERO

30、CHROMATIN PROTEIN 1 (LHP1) assemble on FLC chromatin. (c) As vernalization proceeds, the density of repressive modifications, particularly H3K27triMe and lysine 9 methylation of histone 3 H3K9triMe; mediated by an unknown H3K9 methyltransferase (HMTase) increases. (d) Eventually, a mitotically stabl

31、e state of repression that no longer requires VIN3 is achieved. This mitotically stable state is likely to involve positive feedback loops in which the repressive chromatin modifications serve to recruit the chromatin-modifying plexes including VRN1 to maintain a repressive state. As the FLC locus p

32、asses to the next generation, the active chromatin state represented in (a) is re-established Hormone GA regulates flowering timeGA1: an enzyme involved in GA biosynthesisga1: In addition to the dwarf phenotype, the mutant flowers late under LD conditions and does not flower under SD conditions.GA t

33、reatment promotes flowering time. Flower development in ArabidopsisVegetative meristemInflorescence meristemFloral meristemFlower: sepals, petals, stamens, and carpelsTransition to reproduction: Genes & other factorsFlower organ development:Organ identity genesOne of the early successes of the appli

34、cation of molecular genetics to study plant development was the discovery of a series of genes that act together, in an apparently simple binatorial model, to specify the identity of the different organs of a flower. Widely known as the ABC model, The cast list of genes has been defined and, great p

35、rogress has been made in understanding how they are regulated, how they act together, what they do and how they have contributed to the evolution of the flower in its varied forms. Flower organspetalstamencarpelsepalThe flower is generated from the floral meristem the floral meristemProduced in 4 co

36、ncentric whorls with the same ordersepal (whorl 1)stamen (whorl 3)petal (whorl 2)carpel (whorl 4)Flower organs ABC model (the ap1 mutant is similar)stamen-carpel-stamen-carpelsepal-petal-stamen-carpelwtpistillata (pi)sepal-sepal-carpel-carpelsepal-petal-stamen-carpelapetala3 (ap3)sepal-petal-stamen-

37、carpelsepal-petal-petal-sepalThe “ABC” model for flower developmentThe ABC genes function in the distinct fields. The A and C genes are mutually exclusive in their expression. ABCAP1, AP2AP3, PIAGThe A genes: ap1 or ap2 mutants should (and do) make carpel-stamen-stamen-carpelap1 or ap2WTThe B genes:

38、 ap3 or pi mutants should (and do) make sepal-sepal-carpel-carpelWTap3 or piThe C genes: ag mutants should (and do) make sepal-petal-petal-sepalWTagMADS-box proteins (MCM1, AG, DEF, SRF)Plant MADS-box proteins belong to two large families: the type I class, which group with the human SRF protein, an

39、d the type II class that groups with yeast MEF2ABCE model (A)BC model Gametogenesis and FertilizationFlower organ function:generative cellDiploid pollen mother cells undergo meiosis to produce a tetrad of haploid microspores. Each microspore develops into a pollen grain containing two haploid cells (mitosis I):the generative cell (small)The vegetative cell (large)Male gametogenesisthe vegetative cell grows to produce the pollen tubethe generative cell produce 2 sperm cells (mitosis II