BIOSYNTHESIS OF GA_AYAN PRADHAN_H-2024-001-D.pptx

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1. BIOSYNTHESIS OF GA IN PLANTS Presentation – I under course FLS 601 Department of Floriculture, Medicinal & Aromatic Plants, Faculty of Horticulture, UBKV Submitted by, Ayan Pradhan Ph. D.1 st year 1 st Semester Faculty of Horticulture, UBKV Submitted to, Dr. Soumen Maitra Professor, Department of Floriculture, Medicinal and Aromatic Plants

2. Rice filed with infected plants Root Growth from Infected Node

3. Discovery of Gibberellins Early 1890’s, Gibberellins were discovered by Kurosawa in Japan. He studied abnormal growth in paddy seedlings caused by the fungus Gibberella fujikuroi . In the 1930s, T. Yabuta and T. Hayashi isolated an active compound from the fungus, which they named gibberellin.

4. Gibberellins Diversity Quantity Found Over 60 gibberellins identified in fungi and plants. Seed Plants 51 gibberellins discovered in seed-bearing plants. Species Variation No species contains more than 15 types; most have only a few (Phinney, 1979; Jones and MacMillan, 1984).

5. Structure of GA

6. Structure of GA Gibberelins are a group of tetracyclic diterpenoid carboxylic acid compound made of 4 isoprene unit All the gibberellins are almost similar in structure with either 4 or 5 ring system. They contain a gibbane ring made up of cyclohexane ring and 4-lactone ring. They differ in minute details viz., the number and position of –OH and sometimes –CH3 and –COOH groups at different carbon atoms of the gibbane ring. Till now 136 Gibberelins (only few bioactive) isolated from plants, fungi & bacteria. All the Gibberelins either have 19 carbon atoms (C19 GAs) or 20 Carbon atoms (C20 GAs). C19 are more biologically active than C20. GA3 is the most thoroughly studied gibberellin. Commercially available GAs: GA3, GA4, GA7 3 4 10 6 1 2 5 9

7. Biosynthesis of GA in plants Gibberelins are synthesized by the condensation of 4 isoperine subunits. The basic biological isoprene unit is IPP (Isopentyl Pyrophosphate). Pathway initiating Precursor : Acetyl Co-A Immediate Precursor of GA: ent -Kaurene Gibberellins are synthesized from acetate units of acetyl coenzyme A by the mevalonic pathway. The 3 steps that are involved in the biosynthesis of gibberellins occur in Plastid (Stage-I), ER (Stage-II) & Cytosol (Stage-III) respectively. 4 Main Events Synthesis of GGPP Formation of ent -kaurene Formation of GA12 aldehyde Formation of other Gibberellin form from GA12 aldehyde

8. Stage-I (in Plastid) Acetate esterified with co enzyme to form 3 molecules of Acetyl- CoA Acetyl CoA under series of condensing reaction produce BOG-CoA. This BOG-CoA is reduced to form Mevalonic acid Mevalonic acid is then phosphorylated by Mevalinic acid kinase (in presence of 2 ATP molecules) to form Mevalonic Acid Pyrophosphate The decarboxylation of Mevalonic Acid Pyrophosphate in presence of ATP yields Isopentyl Pyrophosphate ( IpPP ) By the enzyme IpPP isomerase, IpPP is converted to one of its isomer i.e. DMAPP. 1 molecule of DMAPP then serves as an acceptor of 1 IpPP molecule with elimination of Pyrophosphate and formation of GPP GPP with 1 molecule of IpPP forms Farnesol Pyrophosphate (FPP), which accepts another molecule of IpPP to form GGPP (Geranyl Geraniol Pyrophophate ) BOG-CoA : β- hydroxyl- β- methyl glutaryl CoA MA Kinase : Mevalonate Kinase MAP : Mevalonic Acid Pyrophosphate IpPP : Isopentyl Pyrophosphate DMAPP : Dimethylallyl Pyrophosphate GPP : Geraniol Pyrophoshate FPP : Farnesol Pyrophosphate GGPP : Geranyl Geraniol Pyrophosphate CPP : Copallyl Pyrophosphate

9. Stage-II (in ER) ent -kaurene is oxidized step-wise at C-19 to form ent-Kaurenol , ent-kaurenal and ent - Kaurenoic acid. The latter is hydroxylated to ent-7 α- hydroxy Kaurenoic acid. Now the contraction of beta ring & the process of beta hydroxylation begins and ent-7 α- hydroxy Kaurenoic acid gets converted to 20 carbon GA12 aldehyde GA12 aldehyde to GA12 by ent - kaurene acid oxidase enzyme (KAO)

10. Stage-III (in Cytosol) In Cytosol, 2 kinds of hydroxylation occurs viz. Non-C13-Hydroxylation & Early-C13-Hydroxylation Oxidation at 20 th Carbon forming C19 GA compound viz GA9 & GA20 Non-C13-Hydroxylation Early-C13-Hydroxylation

11. GA Inactivation (in Cytosol) Hydroxyla tion at 2 nd Carbon compound Non-C13-Hydroxylation Pathway Early-C13-Hydroxylation Pathway

12. Anti-Gibberellin Anti-Gibberellins AMO 1618 – 2 isopropyl 4,5 methyl ammo-5-methyl phenyl-1-peperidine carboxylate methyl chloride Phosphon -D Ancymidol A-Rest Paclobutrazole CCC: Dichloroethyl Trimethyl Ammonium Chloride

13. Reactivity of GAs on the basis of = bond (More Unsaturated) or (More Reactive) (Less Unsaturated) or (Less Reactive)

14. Plant parts where mostly produced: Apical Tissues & Young Leaves. Highest level of GA found in immature seeds & developing fruits. Developing seeds, fruits (most abundant young expanding organ, buds & embryos) Glucose derivatives ( carbon 2– O , 3– O , 11– O , 13– O , or 17– O ) are the most common conjugated GAs in plants GA3 Glycosides Conjugates ( Glc -Gas ) are stored form of GA in mature seeds. GA liberated from con jugated form by Glucosidase Distribution & Conjugates

15. Gibberellin Movement in Plant Fig.1 : Arrows indicate documented long-distance movement of mobile GAs. The arrows are color-coded to correlate with GA forms shown in the biosynthetic pathway in previous slide. Regnault et al. conducted a series of grafting experiments using Arabidopsis thaliana mutant plants compromised at different stages of GA biosynthesis and identified GA 12 as the major GA form transported over a long distance through the vasculature. GA 12 moved through the xylem in a root-to-shoot manner and in the phloem in a shoot-to-root direction to regulate plant growth.

16. I n plants: Stem elongation, germination, dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence. Function of Gibberellins

17. Different components of GA signaling pathway : A ligand, A receptor, Some inhibitors & Gibberelin response genes Signaling of Gibberellins Gibberelin (GA) Ligand DELLA REPRESSOR Receptor / Repressor DELLA GRAS Example In Rice, SLR 1 In Arabidopsis, GAI & RGA Phytochrome Interacting Factor (PIF) Molecular Chaperons Repressor Target GID 1 Transcription factor- GA insensitive Dwarf 1 26 S Proteasome Transcription factor- 26 S Proteasome Complex

18. REFERENCES Salisbury, F. B., and Ross, C. W. (1992). Plant physiology (4th ed.). Wadsworth Publishing Company, New York. pp. 317-324 Takahashi, N., Phinney, B. O., & MacMillan, J. (Eds.). (2012). Gibberellins. Springer Science & Business Media. Verma, S. K., and Verma, M. (2007). A textbook of plant physiology, biochemistry and biotechnology (6th ed.). S. Chand & Company Ltd. New Delhi. pp. 102-108 Yabuta , T. (1938). On the crystal of gibberellin, a substance to promote plant growth. J . Agric. Chem. Soc. Japan., 14(2):15-26. Zeng C, Cai WJ, Jiang LC, Ye T, Feng YQ. Advancing Glucose Conjugated Gibberellins Discovery: A Structure-Oriented Screening and Identification Method for Unraveling Gibberellin Metabolites in Plants. Metabolites. 2024 Jan 29;14(2):96. doi : 10.3390/metabo14020096. PMID: 38392988; PMCID: PMC10890662.