Genetic Regulations of Photosynthesis _Prakash V

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Creating Intellectual Assets Through Innovation Every day almost one billion people suffer from chronic hunger, and the situation is expected to deteriorate with a projected population growth to 9 billion worldwide by 2050 . The rice yields in Asia need to increase by 60%, a change that may be achieved by introduction of the C4 photosynthetic cycle into rice. The international C4 Rice Consortium was founded in order to test the feasibility of installing C4 photosynthetic engine into rice. Demand for Food Cyclic electron flow around PSI in higher plants consists of at least two partially redundant pathways FQR and NDH Ferredoxin quinone oxidoreductas NAD(P)H dehydrogenase

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GENETIC REGULATIONS of PHOTOSYNTHSIS - ETC AND CARBON ASSIMILATION Fd- dependent electron transport-associated proton transport pathways Creating Intellectual Assets Through Innovation Therefore between cyclic and non-cyclic pathways gives us a degree of flexibility in the ratio of ATP/NAPDH production. Thereby plants can hence adjust the ratio of ATP/NAPDH to meet the needs of metabolism.

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Creating Intellectual Assets Through Innovation Several structural and functional components of the photosynthetic apparatus are responsive to stress, photosystems and Rubisco act as the major stress sensors. Stress sensing is primarily reflected in imbalance in cellular redox homeostasis and changes in cellular sugar level alteration and signaling Signals generated by these changes bring about photochemical, metabolic and molecular reprogramming for stress adaptation through different signal transduction pathways. Genetic factors play an important role to high CO2 conc. The down regulation of Transcripts encoding Rubisco and other proteins involved in CO2 fixation

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Creating Intellectual Assets Through Innovation When the supply of free energy ( photons ) from light is in excess of the needs of metabolism, The ETC emerges with safe dissipation of the excess free energy. 1. PQ 2. Heat 3. NPQ The photosynthetic engine must be able to adjust the relative rates of production of ATP/NADPH in order to prevent limitations on the operation of photosynthesis due to imbalance in the availability of energy. Imbalance

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Creating Intellectual Assets Through Innovation Redox Reactions Ex: Give and take policy, Time value of money, Purchasing power of money and Inflation “ Keep rotating money by investing ”

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Fates of Organic Building Blocks in ATP Metabolism ORGANIC BUILDING BLOCK MOLECULES Monosaccharides Amino acids Acetates Nucleotide bases Polymers & other energy rich molecules CO 2 & H 2 O anabolic processes catabolic processes ATP ADP+P i energy energy Creating Intellectual Assets Through Innovation

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Creating Intellectual Assets Through Innovation Chloroplast and PETC A. The principle sink for electrons produced in chloroplast is Calvin cycle for CO2 assimilation– Photosynthesis B. Apart from photosynthesis, chloroplast is unique site for essential metabolic reactions like… Chlorophyll biosynthesis Fatty acid synthesis Hormones Several steps in Sulphur and Nitrogen metabolism Redox signaling and redox balancing Water –water cycle –ASADA cycle Fd s e - Efficiency

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Creating Intellectual Assets Through Innovation Redox chemistry of PETC and associated redox regulators PSII and PSI – Redox mediators ( Green ) Electron flow from water to NADP – (Thick Black) Redox Transmitters- TRX, NTRC, Ccda HCF164 - ( Yellow ) Minor electrons used for regulatory redox – (Thin black) Influence of regulators on distinct cell process - ( Blue mark ) 1.Anabolic metabolism 2.Antioxidant systems 3.Redox regulatory system QA-----QB-----PQH2-------Cyb6f------PC = slowest process

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Principle approaches to identify the nature and origin of photosynthetic redox signals through Site-specific inhibitors in ETC . DCMU -Dichlorophenyl -dimethyl urea DBMIB- Dibromo-methyl-isopropyl-benzoquinone Creating Intellectual Assets Through Innovation Algae Photo Bioreactor chlamydomonas reinhardtii

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Creating Intellectual Assets Through Innovation Input elements and output acceptors of Redox in PETC signaling Input elements - Fd, NADPH, and GSH Target proteins - FBPase, malate dehydrogenase (MDH), FLN, and AGPase Final acceptors - ROS, RNS, peroxides, and O2 Generation of ROS is stimulated upon metabolic imbalances that usually are induced by sudden environmental changes leading to signaling events. Imbalance b/w energy supply and demand e - e - PQ

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Creating Intellectual Assets Through Innovation Reduced PQ pool and signaling events in plastid transcription The redox state of the PQ pool modulates several independent redox signaling pathways, that serve to regulate photosynthetic efficiency by the transcription and post-translational modification of existing LHCs and RCs proteins. Allen et al 2011 STN7 is important mediator for redox state sensing of PQ-pool

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Creating Intellectual Assets Through Innovation Chloroplast (green), Cytosol (white) Nucleus (yellow). The integrated cellular network consists of two sub-networks. 1. One network is the signaling transduction pathways in the cytosol 2. The gene regulatory network for transcriptional regulation in nucleus. An important mediator for PQ pool redox status is the thylakoid kinase STN7 . STN7 kinase transmits the decisive signal to the nucleus, resulting in the ensuing regulation of the relative amount of each of the photosystems. In this study, the gene regulatory network (protein-DNA interaction) in the nucleus is constructed under different retrograde signals originating from different redox states in the PQ pool. Effect of light quality on gene expression The mechanism by which the redox signal is transmitted from the chloroplast double membrane into the cytosol is poorly understood ?

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Thioredoxin Reductase Type C (NTRC) Enhanced Thermotolerance in Arabidopsis by Its Redox-Dependent Holdase Chaperone Function- March 2013 Creating Intellectual Assets Through Innovation In conclusion, our study reveals novel functions of NTRC working specifically in plant chloroplasts provides enhanced thermotolerance to plants against high light and temperature stress Phenotype for drought and radiation use efficiency (photosynthesis efficiency, source to sink) is a challenge in phenotyping methods - BIRAC

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Redox regulation in plastid starch and lipid synthesis Creating Intellectual Assets Through Innovation A ACCase ( Acetyl-CoA carboxylase ) and MGD ( mono- galactosyldiacylglycerol synthase ) in plastid lipid synthesis are activated by Trx transmitters AGPase plays a key role in starch synthesis in plastid, is activated by reduction of a disulfide by Trx-f and Trx-m A good correlation exists between Suc. concentration , reduction state PQ , and starch synthesis

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Creating Intellectual Assets Through Innovation Acclimation of photosynthesis in C3 plants to high CO2 CO2  Sudden  Photosynthesis Sudden  Photorespiration CO2/O2  Photosynthesis Yield Growth Rapid inhibitory effect on Ph. Sy . genes Alteration in source and sink relationship Insufficient sink capacity and  in CHO Substantial reprograming of gene expression. Down regulation of Ph.Sy. Genes RuBisCO activity  Up-regulation of RuBP regeneration Starch synthesis

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Creating Intellectual Assets Through Innovation THNAK YOU Next…….GENETIC REGULATIONS OF C3 and C4 CARBON ASSIMILATION Prakash V Bioseed Research India Ltd. Biotech R&D Center- ICRISAT Campus Hyderabad

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