Cytokinis biosynthesis and transduction

Class presentation on Cytokinis biosynthesis and transduction

1. PP 503: Physiological and molecular responses of plant to abiotic stresses (2+1) Cytokinin Biosynthesis and transduction 1 Presented by: Ekatpure Sachin Chandrakant (PhD Research Scholar)

2. What is a hormone? Biochemical which regulates growth based on biological and environmental influences Synonyms : Plant hormones, plant growth regulators (PGRs), Phytohormone Regulate growth and development Mobile throughout plant Environment and stress responsive 2

3. Major plant hormones Auxin – Greek: auxein ; to grow or increase Cytokinin – cytokinesis (cell division) Abscisic acid – abscission Jasmonic acid – found in jasmine oil Gibberellic acid – pathogen Gibberella Ethylene – chemical brother to ethanol Brassinosteroids – derived from Brassica spp. 3

4. Cytokinins 4

5. Definition Cytokinins (CK) are a class of plant growth substances ( phyto hormones) that promote cell division, in plant roots and shoots. 5

6. History 1. Discovery : 1913, Gottlieb Haberlandt . 1941, Johannes van Overbeek 1954, Jablonski and Skoog . 2. Isolation: The first cytokinin (kinetin) was isolated in 1955 by Miller The first naturally occurring cytokinin ( zeatin ) was isolated in 1961 by Miller 6

7. Basic chemistry All cytokinins have basic Adenine ring structure. 7

8. Types There are two types of cytokinins : A denine-type cytokinins ; represented by kinetin, zeatin , and 6-benzylaminopurine (6BAP) Phenylurea -type cytokinins like diphenylurea and thidiazuron (TDZ ) 8

9. Produced Cytokinins are produced mainly in the : Roots Fruits Young leaves Developing tissues 9

10. Functions Induce cell division in callus cells in the presence of an Auxin Promote bud or root formation from callus cultures when in the appropriate molar ratios to Auxin Delay senescence of leaves Promote expansion of dicot cotyledons Promote movement of nutrients Promote chloroplast development Promote cell expansion in leaves and cotyledons Regulate growth of stems and roots 10

11. Biosynthesis of Cytokinins 11

12. 1. Biosynthesis 12 An enzyme that synthesis cytokinin called ∆ 2 -isopentenyl- pyrophosphate: AMP transferase or cytokinin synthase Isopentenyl group of ∆ 2 -IPP transferred to the AMP with the help of Prenyl transferase The product of this reaction is isopentenyl adenine ribotide This compound is active as a cytokinin in bioassays And is readily converted to Zeatin and other cytokinins

13. 2. Crown gall cytokinin biosynthesis 13 During Agrobacterium infection: A small portion of Ti plasmid known as T-DNA is incorporated in to host DNA T DNA carries genes necessary for the auxin and cytokinins synthesis known as Opines These opines are not synthesize by plant The T-DNA genes involved in cytokinin biosynthesis known as ipt genes That encodes isopentenyl transferase enzyme That transfers the isopentyl group from isopentenyl pyrophosphate to AMP to form isopentenyl adenine ribotide Isopentenyl adenine ribotide can be converted to the active cytokinins such as trans zeatin and dihydro zeatin by endogenous enzymes in plants

14. 3. Cytokinin Biosynthesis Cytokinins can also be produced by recycled  tRNAs  in plants and bacteria tRNAs with  anticodons  that start with a  uridine  and carrying an already prenylated adenosine adjacent to the anticodon release on degradation the adenosine as a cytokinin The  prenylation  of these adenines is carried out by  tRNA - isopentenyltransferase 14

15. Cytokinin Signaling Transduction 15

16. Histidine Kinases HKs are prevailing sensors in prokaryotes That initiate a signaling system in which phosphoryl groups are transferred between histidines and aspartates ( phosphorelay signaling system) To activate or inhibit similar downstream partners called response regulators (RRs) 16

17. Response regulators The first set of genes to be upregulated in response to cytokinin are the ARR ( A rabidopsis R esponse R egulator) genes In Arabidopsis, response regulators are encoded by a multigene family. They fall into two basic classes : T he type A ARR genes, which are made up solely of a receiver domain, (The rate of transcription of the type-A gene is increased within 10 minutes in response to applied cytokinin) The type B ARR genes, which contain a transcription factor domain in addition to the receiver domain 17

18. Steps to cytokinin signaling AHK (Arabidopsis Histidine Kinase) sensing and signaling, AHP (Arabidopsis Histidine Phosphotasferase) nuclear translocation, ARR (Arabidopsis Response Regulators) transcription activation, and Negative feedback loop through cytokinin-inducible ARR gene products 18

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21. Thank You 21