Una visione sistematica per l’ingegneria metabolica

1. Una visione sistematica per l’ingegneria metabolica Creazione di vie metaboliche

2. + + + + TF Ingegneria metabolica probabilmente efficace probab. inefficace (1) (2) (3) (4) (5) (6) (7) (8) (9) S S S S S S S S S A A A A A A A A A Y E B B B B B B B B B Z W X C C C F C C C C C Q P P P Q P P P P P P ATP

3. (3) (4) S S A A E B B C C F Q P P Q Espressione di nuovi enzimi Manipolazioni efficaci che riguardano uno o pochi enzimi Golden rice Polyesters Palatinosio in Sugarcane Dhurrin (glucosidi cianogenici)

4. Produzione di glucosidi cianogenici Tattersall et al., 2001 Science 293:1826-1828

5. Via biosintetica della Dhurrina Two multifunctional microsomal cytochromes P450 (CYP79A1 and CYP71E1) and a soluble UDPG-glucosyltransferase (sbHMNGT)

6. As with S. bicolor, pathway intermediates in these A. thaliana plants were hardly detectable. Plants expressing all three dhurrin biosynthetic pathway genes also accumulated hydroxybenzylglucosinolate, although at much lower levels. CYP79A1 and CYP71E1 CYP79A1, CYP71E1 and sbHMNGT wt

7. Effetto dell’accumulo su insetti A. thaliana leaves containing dhurrin inhibit flea beetle and larvae feeding. (A) Adult beetles fed extensively only on leaves containing no dhurrin. (B) Larvae (indicated by arrows) frequently initiated no mines on leaves containing dhurrin, although attempts were made to feed (indicated by circles). Scale bar, 2.5 mm.

8. Effetto sulle larve Nearly all larvae (98%) presented to leaves containing about 4 mg of dhurrin/gfw died. Transgenic A. thaliana plants released high levels of HCN, up to 2 μmol/gfw, upon tissue damage. An endogenous β-glucosidase with dhurrin hydrolyzing activity is present in A. thaliana. Consumption of leaf-disc material from the transgenic lines expressing the two cytochrome P450 genes (CYP79A1 and CYP71E1), or the UDPG-glucosyltransferase gene (sbHMNGT), or containing the two empty expression vectors was not significantly different from the consumption of leaf-disc material from wt plants.

9. Apparentemente nessun fenotipo “forte” in assenza di insetti Event. una lieve riduzione nella crescita a 4 mg/gfw

10. Kristensen et al., 2005 PNAS 102:1779-84 1X 2X 3X • Kristensen C eta al., (2005) Metabolic engineering of dhurrin in transgenic Arabidopsis plants with marginal inadvertent effects on the metabolome and transcriptome. Proc Natl Acad Sci U S A. 102:1779-84.

11. Fenotipo delle piante Transgenic Arabidopsis phenotypes. Eighteen independent 1x lines were generated by transforming wild type (wt) with sorghum CYP79A1. Ten independent 2x lines were generated by transformation with both CYP79A1 and CYP71E1. Two 3x lines were generated by retransforming the 2x.7 and 2x.8 lines with sorghum UGT85B1.

12. Wt 1X 2X 3X 1X accumulated 2–3% of its dry matter as tyrosine-derived hydroxybenzylglucosinolate Comparison of plant morphology and metabolite composition Plants expressing sorghum CYP79A1 are designated 1x, plants expressing sorghum CYP79A1 and CYP71E1 are designated 2x, and plants expressing CYP79A1, CYP71E1, and UGT85B1 are designated 3x. Morphological phenotype (A) and metabolite profile as monitored as total ion trace (TIC) and extracted ion chromatographs (EIC) in the three transgenic lines are shown (B).

13. Wt 1X 2X 3X the 2x plant line accumulated 6-fold less phydroxybenzylglucosinolate (n. 7 and 8) in comparison with the 1x plant line. Major glucosides in 3X: p-glucosyloxy-benzoic acid (3), p-hydroxybenzoylglucose (5), p-glucosyloxybenzoylglucose (1) Predicted accumulation of dhurrin (6) in large amounts (C) Close-ups of the extracted ion chromatograms to facilitate visualization of minor components. Compound numbers and absolute and relative changes are tabulated in Table 1. the level of sinapoylglucose (14), sinapoylmalate (13) kaempferol-3-O-glucoside-7-O-rhamnoside (15), kaempferol-3-Orhamnoside-7-O-rhamnoside (16), and kaempferol-3-O-[rhamnosyl(132)glucoside]-7-O-rhamnoside (17) in 2x plants was reduced.

14. Metabolic profiling of wild-type and transgenic A. thaliana lines +, Metabolite present with relative amounts indicated by the number of plus signs. –, Metabolite was not detected; rt, retention time. *Metabolites marked derived from p-hydroxyphenylacetaldoxime. †Metabolites marked derived from p-hydroxymandelonitrile (6). Compared with wild-type plants, the level of sinapoylglucose (no. 14, rt 18.4 min), the shared precursor for sinapoylcholine and sinapoylmalate, was found to be 7 fold down-regulated.

15. Vie alternative 1X 2X 3X Sinalbin (p-hydroxybenzyl glucosinolate)

16. No effect on aa pools Non sembra esserci una riduzione significativa nel contenuto dei vari aa, tirosina compresa Nonostante l’enorme flusso che passa attraverso la Phe/Tyr, il livello non è calato significativamente  la sintesi è controllata dal demand

17. Via biosintetica del sinapato

18. Forse uno dei metaboliti che si accumulano nella pianta 2X (es derivati del benzoilglucosio) inibisce qualche enzima della via del sinapato a motivo della somiglianza Sinapate

19. Surprisingly, metabolite profiling of the 2x plants revealed that sinapoylmalate (no. 13), sinapoylglucose (no. 14), and kaempferol glucoside (nos. 15, 16, and 17) levels were decreased compared with wild-type plants (Fig. 2 and Table 1). Sinapoylmalate and sinapoylglucose serve as UV protectants and constitute the major sinapate esters in A. thaliana leaves (27). Several mutants with impaired sinapoylmalate levels, designated reduced epidermal fluorescence (ref ) mutants have been characterized (28). The ref2 mutant has decreased lignin content and 3-fold-reduced sinapate ester levels (29). The ref2 mutant is defective in CYP83A1, one of the two oxime-metabolizing cytochrome P450s in glucosinolate biosynthesis (30, 31). It has been suggested that accumulation of oximes or their degradation products perturbs the biosynthesis of phenylpropanoids. In S. bicolor, CYP79A1, CYP71E1, and UGT85B1 have been argued to form a dhurrin-producing metabolon, defined as a multienzyme complex that facilitates channeling of the intermediates in dhurrin synthesis. In the 3x plant line, no p-hydroxybenzylglucosinolate is detectable. This finding augments the proposition that UGT85B1 interacts or colocalizes with CYP79A1 and CYP71E1, thereby excluding p-hydroxybenzylglucosinolate formation

20. Essenzialmente nessun cambiamento nel trascrittoma Ogni punto nel grafico dà il valore di espressione di un gene nel wt (ascissa) e nel mutante (ordinata). I dati per A,B e C sono fatti con un chip specifico (453 geni*), mentre D contiene 27,216 probes. Le linee blu indicano le zone corrispondenti ad un aumento nell’espressione di 2 o 4 volte. The 1x, 2x, and 3x transgenic lines were first analyzed by using the focused array. Arbitrarily, a twofold induction or reduction has traditionally been used to select differentially expressed genes in microarray experiments. Using this criterion, only two endogenous genes were selected as differentially expressed in the 3x line, and no genes were selected in the 1x and 2x lines.

21. Conclusioni The 1x and 3x plants share three common characteristics: (i) no obvious morphological phenotype, (ii) accumulation of large amounts of a tyrosine derived natural product (iii) no evident impact of transgene insertion and expression on the metabolome and transcriptome. -The high levels of phydroxybenzylglucosinolate in 1x A. thaliana plants (n.7 and 8), would support that CYP79A1 associates, interacts, or at least colocalizes with the endogenous post-oxime metabolizing enzymes in glucosinolate synthesis i.e., CYP83A1 or CYP83B1. -Introduction of UGT85B1 facilitated not only rescue of the stressed and stunted phenotype but also eliminated the large majority of novel metabolites observed to accumulate in the 2x plants and the impact on the transcriptome. -The steady-state transcriptional level of the three sorghum genes CYP79A1, CYP71E1, and UGT85B1 was not detected as highly elevated over background levels in the transgenic plants (Fig. 3).

22. Increased metabolic flux from tyrosine into dhurrin in the 3x plants was neither accompanied by changes in the transcriptome nor in the pool of free amino acids. Aromatic amino acids are derived from the shikimate acid pathway and are precursors for a vast array of secondary metabolites (37, 38). Up to 20% of the carbon flow in plants passes through the shikimate pathway (39). Aromatic amino acid biosynthesis in plants is allosterically regulated at the enzyme level to accommodate rapid changes in flux and demands for aromatic amino acid-derived natural products (39, 40). Our combined analyses of the morphological phenotypes, and of metabolite and transcriptome profiles of the transgenic plants used in this study, demonstrate that insertion of an entire high-flux pathway into a transgenic plant is achievable without pleiotropic side effects. The flexibility of the shikimate pathway is demonstrated by the fact that we have increased the dry-weight matter of a tyrosine-derived metabolite to 4% with no impact on free amino acid pools, and without changing the steady-state transcriptional level of genes encoding enzymes in aromatic amino acid biosynthesis. Our data support that formation of metabolons serve to facilitate metabolic channeling to prevent escape of toxic and labile intermediates and to avoid interference with other parts of basic metabolism at all levels (22). The 1x and 2x plants used in this study illustrate this phenomenon. In the 2x plants, the predicted result of gene insertion would be formation of a labile and toxic cyanohydrin. The 2x plant counteracts the accumulation of the cyanohydrin by metabolism and detoxification reactions, as is evident from the altered phenotype, the altered metabolite profile showing accumulation of detoxification products, and the changes in transcriptome profile. In comparison with the metabolic and transcriptome changes that have typically been encountered as a result of changed growth conditions or mutations (e.g., refs. 41–44), the changes in metabolite and transcriptome profiles in the 2x plants were minor. Thus, targeted introduction of traits by genetic engineering based on a solid knowledge of plant metabolism offers the opportunity to generate cultivars that more strictly adhere to the principle of substantial equivalence than cultivars generated by classical breeding procedures.

23. Metabolon formation UGT85B1-YFP was enzymatically active and able to ensure fast and efficient conversion of the labile p-hydroxymandelonitrile into dhurrin. Tight interaction between the two cytochromes P450 was necessary for efficient substrate channelling ] CYP71E1-CFP riduce di molto la sintesi  CFP inibisce l’interazione Fig. 2. Metabolon composed of the two membrane bound cytochromes P450 CYP79A1 and CYP71E1 and the cytosolic UGT85B1 localized at the cytosolic surface of the endoplasmic reticulum. An NADPH dependent membrane bound NADPH-cytochrome P450 oxidoreductase provides reducing power in the form of single electrons. Nielsen et al., (2008) Phytochemistry 69:88-98

25. Plants expressing CYP79A1, CYP71E1, UGT85B1-YFP and free CFP Enhanced accumulation of UGT85B1-YFP towards the plasma membrane UGT85B1-YFP in the presence of CYP79A1 and CYP71E1 (B & E) did not match the cytosolic distribution of free CFP (A & D) Free CFP signal UGT85B1-YFP signal  possibility of in planta formation of a specific ER-localized dhurrin metabolon comprised of CYP79A1, CYP71E1 and UGT85B1

26. Neutral Red staining CFP large central vacuole Visualization of the of the vacuoles as dark areas following incubation with Neutral Red UGT85B1-YFP (da sola)  Il segnale della UGT85B1-YFP cambia Metabolon formation! Co-expression with CYP79A1 and CYP71E1

27. Bibliografia • Tattersall DB et al., (2001) Resistance to an herbivore through engineered cyanogenic glucoside synthesis. Science 293:1826-8. • Kristensen C et al., (2005) Metabolic engineering of dhurrin in transgenic Arabidopsis plants with marginal inadvertent effects on the metabolome and transcriptome. Proc Natl Acad Sci U S A. 102:1779-84. • Nielsen et al., (2008) Metabolon formation in dhurrin biosynthesis. Phytochemistry 69:88-98. • Jørgensen et al. (2005) Cassava Plants with a Depleted Cyanogenic Glucoside Content in Leaves and Tubers. Distribution of Cyanogenic Glucosides, Their Site of Synthesis and Transport, and Blockage of the Biosynthesis by RNA Interference Technology. Plant Physiology 139:363-374. • Poirier Y. (2001) Production of polyesters in transgenic plants. Adv Biochem Eng Biotechnol. 71:209-40. Review.