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1 Engineering Rubisco Activase from Thermophilic Cyanobacteria into High-Temperature Sensitive Plants Chukwuma C. Ogbaga, 1,* Piotr Stepien, 2 Habib-ur-RehmanAthar, 3 Muhammad Ashraf 4 1 Department of Biological Sciences, Nile University of Nigeria, Airport Road, Abuja, Nigeria 2 Department of Plant Nutrition, Wroclaw University of Environmental and Life Sciences, ul.Grunwaldzka 53,50-357 Wroclaw, Poland 3 Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan, Pakistan 4 Pakistan Science Foundation, Islamabad, Pakistan *Corresponding author: Chukwuma C. Ogbaga Nile University of Nigeria, Airport road, Abuja, Nigeria Telephone : +2349030333632 Email:
[email protected] 2 Table of Contents Abstract Abbreviations Introduction I RUBISCO/RUBISCO ACTIVASE A. Structure and Function II CHAPERONINS AND HEAT SHOCK PROTEINS III ALTERNATIVE SPLICING IV CYANOBACTERIA (PHOTOSYNTHETIC BACTERIA) V THERMOPHILIC CYANOBACTERIA VI HIGHER CROPS AND PLANTS A. Alternative splicing of RCA gene in rice affects Rubsico thermotolerance B. Increase in temperature lowers Rubisco activity in maize VII ENGINEERING RUBISCOACTIVASE FROM THERMOPHILIC CYANOBACTERIA INTO HIGH TEMPERATURE SENSITIVE BIOMASS PLANTS Conclusion References 3 Abstract In the past decade, various strategies to improve photosynthesis and crop yield, such as leaf morphology, light interception and use efficiency, biochemistry of light reactions, stomatal conductance, carboxylation efficiency, and source to sink regulation , have been discussed at length. Leaf morphology and physiology are tightly coupled with light capturing efficiency, gas exchange capacity, and temperature regulation. However, apart from the photoprotective mechanism of photosystem-II (PSII), i.e. non-photochemical quenching, very low genetic variation in the components of light reactions has been observed in plants. In the last decade, biochemistry-based enhancement of carboxylation efficiency that improves photosynthesis in plants was one of the potential strategies for improving plant biomass production. Enhancement of activation of the ubiquitous enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) by Rubisco activase may be another potential strategy for improving a photosynthesis-driven increase in crop yield. Rubisco activase modifies the conformation of the active center in Rubisco by removing tightly bound inhibitors, thereby contributing to enzyme activation and rapid carboxylation. Thermophilic cyanobacteria are oxygenic photosynthetic bacteria that thrive in high temperature environments. This critical review discusses the prospects for and the potential of engineering Rubisco activase from thermophilic cyanobacteria into temperature-sensitive plants, to increase the threshold temperature and survival of these plants in arid regions. Key terms: Photosystem II; Photosynthesis; CO 2 fixation; Heat stress; Drought; Higher Plants 4 Abbreviations ATP, adenosine triphosphate; CA, carbonic anhydrase; CA1P, 2-carboxy-D-arabinitol 1- phosphate; CCM, carbon-concentrating mechanism;cyt b 6 f; cytochrome b 6 f complex;Cytc550, cytochrome c550; ETC, electron transport chain; ETR, electron transfer rate; HSP; heat shock protein; LHC, light-harvesting complex; PC, plastocyanin; PG, phosphoglycolate; PQ; plastoquinone; PsbU, luminal peripheral protein in PSII; PSII, photosystem II; RCA, Rubisco activase;RbcL,Rubisco large subunit; RbcS, Rubisco small subunit; RuBP, D-ribulose-1,5-bisphosphate 5 Introduction Over the last century, there has been a massive rise in food and energy demands because of population growth, which has led to an increase in their consumption and production costs (Kearney, 2010; McMichael et al., 2007). Complacent attitudes towards the rising demands for food and energy could potentially result in their shortage in the near future. Simultaneously, continuous fossil fuel use contributes to climate change due to the increase in greenhouse gases (IPCC, 2013, 2014). In addition to polluting the environment, greenhouse gases provoke serious human health problems (McMichael et al., 2007).Therefore, there is a need to grow more food with a simultaneous reduction in emissions; however, land availability limits the former. Appropriation of arable land from rainforests has been considered but the destruction of these habitats is neither sustainable nor desirable (Alongi, 2002; Tilman et al., 2002). To reduce emissions, renewable energy use has also been considered (Fridleifsson, 2001; Jacobson and Delucchi, 2011; Panwar et al., 2011); however, their current limitations include requirement of liquid fuels and competition with food-based agriculture. There is an overall need to utilize limited land for maximum food and energy production. Biofuels and biomass crops emit small amounts of greenhouse gases and are sustainable; thus, they are more appropriate for food and energy production (Escobar et al., 2009). However, temperature extremes can limit growth of biomass crops on both arable and marginal lands, thereby limiting their application (McKendry, 2002). Hence, a better understanding of the effects of extreme temperatures on suitable high-biomass plants is required. Under extreme temperatures, plants close their stomata to conserve water, which restricts CO 2 supply and reduces photosynthesis. Heat stress may also directly inhibit photosynthesis. Further absorption of sunlight under high temperature conditions leads to the formation of
