1、第四章,赤霉素,生物合成,微生物中的合成途径,植物中的合成途径,在微生物中的合成途径,Gibberellin (GA)-biosynthetic pathways in Fusarium fujikuroi, indicating reactions of the main (3-hydroxylated) and the minor (non-hydroxylated) pathways as well as side reactions catalysed by the enzyme P450-1. All reactions affected in the cpr-Gf mutant a
2、nd dependent on cytochrome P450 oxidoreductase (CPR) are marked. Dotted arrows Proposed sequence of reactions. GGPP Geranylgeranyl diphosphate, CPPent-copalyl diphosphate,Tudzynski， Appl Microbiol Biotechnol (2005) 66: 597611,Thomas and Sun， Plant Physiology, June 2004, Vol. 135, pp. 668676,在植物中的合成途
3、径,比较在微生物与植物中合成途径的差异,Tudzynski，Appl Microbiol Biotechnol (2005) 66: 597611,赤霉素的代谢途径,Olszewski, et al., The Plant Cell, S61S80, Supplement 2002,Inactivecatabolites,赤霉素合成缺失突变体,Phenotype of GA-deficient mutants in Arabidopsis and in barley. A, Five-week-old wild-type (WT) Arabidopsis and the GA-deficien
4、t ga1-3 mutant. B, Two-week-old WT Himalaya and a GA-deficient mutant grd2 (Chandler and Robertson, 1999).,Thomas and Sun， Plant Physiology, June 2004, Vol. 135, pp. 668676,WT,ga1-3,WT,grd2,GA突变体,Barley GA Mutants.Plants are of equal age and are (from left to right) Himalaya (wild type), grd2 (GA-de
5、ficient putative GA3ox mutant Chandler andRobertson, 1999), Sln1d (dominant dwarf), and sln1c (slender).,Olszewski, The Plant Cell, S61S80, Supplement 2002,sln1c,sln1d,grd2,WT,施用GA会促进植物伸长,Fig. 1. Three-week-old pumpkin seedlings, treated with GA4 and/or the GA-biosynthesis inhibitor LAB150978 (Jung
6、et al. 1986). Treatment from left to right: control, GA4 (10)6 M), LAB150978 (10)6 M), and GA4 plus LAB150978 (both 10)6 M),Lange， Planta (1998) 204: 409419,control,加GA4,加GA4合成抑制剂,同时加GA4和GA4合成抑制剂,赤霉素信号转导,Thomas and Sun, Plant Physiology, June 2004, Vol. 135, pp. 668676,Gomi and Matsuoka Current Opin
7、ion in Plant Biology 2003, 6:489493,In the absence of GA, DELLA protein (SLR1/RGA) directly or indirectly inhibitsthe expression of GA-induced genes, including GAMYB. KGM inhibits GAMYB activity by phosphorylation. SPY activates the negative regulator andinhibits the activity of the positive regulat
8、or by O-GlcNAc modification. GA binds to an unidentified GA receptor(s) and activates G proteins (D1) that enhance the GA signal. PHOR1 is translocated into the nucleus, where it acts as a positive regulator by GA signalling. The GA signal also activates protein kinase and GID1 to trigger GID2/SLY1-
9、mediated degradation of SLR1/RGA. 14-3-3 proteins regulate the subcellular localisation of RSG,which controls the expression of the ent-kaurene oxidase gene.,Possible roles of recently identified factors in the GA signalling pathway.,GA,GA biosynthetic and catabolic enzymes, and feedback regulation
10、of GA biosynthesis by the GA-response pathway.,Bioactive GAs are synthesized from geranyl geranyl diphosphate via multiple enzymes that catalyze sequential steps in the pathway. Boxed italic text indicates metabolites. T-bars indicate the inhibition of gene expression, the block arrow indicates the
11、promotion of gene expression. GA homeostasis is achieved by a feedback mechanism. An elevated activity in the GA-response pathway downregulates transcript levels of some of the GA20ox and GA3ox genes, but upregulates transcript levels of GA2ox genes. CPS, copalyl diphosphate synthase; GA2ox, GA 2-ox
12、idase (encoded by multiple genes); GA3ox, GA 3-oxidase (encoded by multiple genes); GA20ox, GA 20-oxidase (encoded by multiple genes); KAO, ent-kaurenoic acid oxidase; KO, ent-kaurene oxidase; KS, ent-kaurene synthase.,Fleet and Sun, Current Opinion in Plant Biology 2005, 8:7785,赤霉素调控不同发育基因的表达,Model
13、 of the GA signaling pathway. Ovals represent transcriptionfactors, gray lines indicate hypothesized interactions. Arrows and T-bars indicate direct or indirect activation and inhibition, respectively. B genes encode PI and AP3; the C gene in this pathway encodes AGAMOUS; DELLA includes RGA, GAI, RG
14、Ls, SLR1, SLN1, and other orthologs. *PKL inhibits embryonic cell fate duringpost-embryonic development.,Fleet and Sun, Current Opinion in Plant Biology 2005, 8:7785,赤霉素调控花发育的分子机制,Activation of a hypothetical transmembrane receptor by GA inhibitsrepressors of GA signaling. These repressors are encod
15、ed by theRGA, GAI, and RGL genes. The SPY gene also represses GA signalingand genetically acts upstream of RGA and GAI. It may act topromote the activity of GAI/RGA/RGL by GlcNAc modification, inwhich case GA signaling may inhibit GAI/RGA/RGAL by repressingSPY function. PHOR1 has not been described
16、in Arabidopsis, buthas been shown to be involved in GA signaling in potato. Its possibleinvolvement in ubiquitination and protein degradation leads tothe tentative proposal that it is involved in the demonstrated degradationof the repressing protein RGA in response to GA. The floralmeristem identity
17、 gene LFY is upregulated at the transcriptional levelby GA. The flowering-time gene SOC1 is also upregulated by GA,whereas FPF1 and GA-MYB were proposed to mediate betweenGAs and the regulation of flowering time. These three genes maytherefore act downstream of GAI/RGA/RGL but upstream of LFY.The da
18、ta underlying this scheme are described in detail in the text.,Mouradov et al., The Plant Cell, S111S130, Supplement 2002,赤霉素在调控开花中的作用,Mouradov et al., The Plant Cell, S111S130, Supplement 2002,Figure 2. The KNOX pathway and shoot development. A: Insitu hybridization of SHOOTMERISTEMLESS (STM) in an
19、Arabidopsis shoot apex. STM expression marks the shootapical meristem (SAM) and its absence marks the leaf foundercells (FC) and leaves. B: Cartoon showing genetic interactionsin the shoot apex (KNOXgenes shownin white, hormone genesin black and other transcription factors in red). STM is expressedt
20、hroughout the SAM (purple) but is absent from leaffounder cells and leaves (shown in green). The expression ofASYMMETRIC LEAVES1 (AS1) and AS2 is excluded from theSAM and restricted to leaves. STM negatively regulates AS1and AS2 within the SAM, and downregulation of STM in leavesallowsAS1and AS2expr
21、ession.AS1and AS2act together as aheterodimer to negatively regulate the KNOX genes BP,KNAT2 and KNAT6 thereby restricting their expression to theSAM. YABBY (YAB) genes are expressed in the abaxialdomain of the leaf (shown in yellow) and repress BP and STMexpression (regulation of STM not depicted).
22、 The GA biosyntheticgene AtGA20ox1 is in turn repressed by STM, restrictingits expression to the leaf. Both STM and BP can formheterodimers with the BLH homeodomain protein BELLRINGER(BLR)/PENNYWISE (PNY) in the SAM (indicated by .-.).,Hay et al., BioEssays 26:395404, 2004,赤霉素与KNOX基因的关系,KNOX directl
23、y represses GA 20 oxidase expression in the SAM, thus allowing normal shoot development. Increased GA activity enhances the effect of decreased KNOX function, thus preventing shoot development. AD (adapted from Sakamoto T et al., Genes and Development, 2001,15: 581590 with the permission of Cold Spr
24、ing Harbor Laboratory Press.): Mutually exclusive expression patterns of NTH15 (A) and Ntc12 (B) mRNA in a tobacco shoot apex. Mutation in the NTH15-binding sequence expands the wild-type Ntc12 expression pattern (C: Ntc12-w.t.) to the corpus of the SAM (D: Ntc12-m2). EH (adapted from Hay A et al.,
25、Current Biology 2002,12,15571565 with permission of Elsevier): ConstitutiveGAsignalling in an stm-2 background results in failure to initiate a SAM. Aerial view of Arabidopsis plants of the following genotypes: E: spy-5, F: stm-2, G: wild type, H: stm-2;spy-5. The spy mutation(97) is used in these e
26、xperiments to confer constitutive GA signalling to the plant but may affect additional processes that have not yet been described.,Hay et al., BioEssays 26:395404, 2004,在叶子发育过程中赤霉素与KNOX的调控关系,Hay et al., BioEssays 26:395404, 2004,在植物生长的过程中KNOX基因与植物激素之间的调控关系,Figure 5. Regulation of hormone activities
27、by KNOX proteinsin the shoot apex. This cartoon represents a longitudinal view ofa shoot apex. KNOX expression in the SAM (shown in pink) promotes cytokinin synthesis (shown as a purple gradient) and cytokinin may in turn promote KNOX expression in the SAM (dashed arrow). KNOX represses GA synthesis
28、 (and may promote breakdown of GA) such that GA activity is confined to leaves (shown in green). Auxin (IAA) gradients predict the site of leaf inception (shown as a yellow arrowhead) and promote primordium outgrowth and vascular differentiation (shown as yellow arrows). KNOX expression may be repre
29、ssed in regionsof high IAA;,Hay et al., BioEssays 26:395404, 2004,KNOX在植物发育过程中的作用,Figure 6. KNOX transcription factors have multiple inputsinto growth regulation. KNOX activates cytokinin biosynthesis,which in turn activates cell division. KNOX represses GA biosynthesis, and this may regulate cytosk
30、eletal arrangements that control cell differentiation. Cell differentiation is also suppressed by the direct regulation of cell wall biosynthesis by KNOX. GA and auxin activate expression of the cell wallloosening proteins, expansins, therefore KNOX regulation of hormone homeostasis may indirectly r
31、egulate cell wall structure. Changes in cell division may feedback to regulate KNOX gene expression.,Hay et al., BioEssays 26:395404, 2004,Overexpression of miR159a delays the floral transition in short days (SDs).,Achard,et al., Development 131, 3357-3365,Micro RNA参与GA调控作用,Fleet and Sun Current Opi
32、nion in Plant Biology 2005, 8:7785,Roles for hormones other than GA are indicated only when they interact with GA functions. Large arrows indicate changes in developmental stage. Italic text indicates a developmental process that is affected by the indicated hormones.T-bars denote inhibition of the
33、indicated process, whereas black arrows denote promotion. Gray arrows denote a hypothesized role (on the basis of data from microarray analysis of transcripts in germinating seeds treated with GA). Two hormones showing synergistic interaction are denoted by a + between them; this does not imply an o
34、rdering of their activities. ABA, abscisic acid.,Interaction of GA with other hormones,目前发现参与GA调控形态发生作用的 基因,Fleet and Sun Current Opinion in Plant Biology 2005, 8:7785,pathway involving multiple enzymes and cellular components. The main, and possibly only, consequence of the perception of active GAs
35、 (such as GA4 in Arabidopsis) is the degradation of various DELLA proteins (such as GAI) via the SCFSLY1 E3 ubiquitin ligase complex. DELLA protein levels are also regulated by auxin and ethylene, raising the possibility that the DELLA proteins are general regulators of plant growth that are regulat
36、ed by several plant hormones rather than being specific components of GA signal transduction. Abbreviations: CPP, copalyl diphosphate; CPS, copalyl diphosphate synthase; GGPP, geranylgeranyl diphosphate; KO, ent-kaurene oxidase; KS, ent-kaurene synthase.,Swain and Singh， TRENDS in Plant Science Vol.
37、10 No.3 March 2005,GA biosynthesis and DELLA proteins. GAs are synthesized via a complex,Fig. 3. GA responses, including stem elongation, are promoted by degradation of repressive GAI and RGA functions. SPY might also negatively regulate stem elongation downstream of GAI and RGA or by modulating the
38、ir activity via GlcNAc-modification. This model has been proposed because the elongated spy phenotype, a phenocopy of GA over-stimulation, is epistatic to dwarfed gai and rga gain-of-function mutant phenotypes. Another GA response is reduced transcription of GA20ox leading to reduced GA levels. Scen
39、arios can be envisioned for how GA might affect stem elongation via microtubule dynamics directly or indirectly involving KSS and/or other microtubule-associated proteins (MAPs). First, a feedback loop might exist between GA levels and KSS expression. GA enhances KSS mRNA levels whereas KSS might do
40、wn-regulate GA levels because kss mutants exhibit loss of GA20ox repression by GA. Second, although highly speculative, SPY could affect the activity of KSS or other MAPs via GlcNAc-modifi- cation, and this apparent repression could be alleviated by GA in a manner similarto that observed for GAI and
41、 RGA.,Foster, et al., TRENDS in Plant Science Vol.8 No.5 May 2003,Possible interactions between gibberellin (GA) signaling and microtubule (MT) dynamics.,GA信号转导的泛素化通道,Figure 1. Key steps in the pathway of polyubiquitylation by SCF E3 ligase, which targets substrate protein and leads to degradation b
42、y the 26S proteasome. (a) Ubiquitin (Ub) is linked via a thioester bond to the ubiquitin-activating enzyme (E1). Ubiquitin is transferred from E1 to the cysteine of the ubiquitin-conjugating enzyme (E2). (b) The SCF E3 ubiquitin ligase (Skp1, cullin, F-box and Rbx1) catalyses the transfer of ubiquitin from E2 to a lysine residue on the substrate protein. Formation of a polyubiquitin chain on the substrate protein targets it for degradation by the 26S proteasome.,Itoh1, et al., TRENDS in Plant Science Vol.8 No.10 October 2003,
