Review article Enhancing C3 photosynthesis: an outlook on feasible interventions for crop improvement Jitender Singh 1,2 , Prachi Pandey 1 , Donald James 1 , Kottakota Chandrasekhar 1 , V. Mohan Murali Achary 1 , Tanushri Kaul 1 , Baishnab C. Tripathy 2 and Malireddy K. Reddy 1, * 1 Plant Molecular Biology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India 2 School of Life Sciences, Jawaharlal Nehru University, New Delhi, India Received 3 April 2014; revised 14 July 2014; accepted 20 July 2014. *Correspondence (Tel +91 11 26741358; fax +91 11 26742316; email reddy@icgeb.res.in) Keywords: C3 photosynthesis, crop improvement, RuBisCO, RuBisCO activase, photorespiration, carbon concentrating mechanisms. Summary Despite the declarations and collective measures taken to eradicate hunger at World Food Summits, food security remains one of the biggest issues that we are faced with. The current scenario could worsen due to the alarming increase in world population, further compounded by adverse climatic conditions, such as increase in atmospheric temperature, unforeseen droughts and decreasing soil moisture, which will decrease crop yield even further. Furthermore, the projected increase in yields of C3 crops as a result of increasing atmospheric CO 2 concentrations is much less than anticipated. Thus, there is an urgent need to increase crop productivity beyond existing yield potentials to address the challenge of food security. One of the domains of plant biology that promises hope in overcoming this problem is study of C3 photosynthesis. In this review, we have examined the potential bottlenecks of C3 photosynthesis and the strategies undertaken to overcome them. The targets considered for possible intervention include RuBisCO, RuBisCO activase, Calvin–Benson–Bassham cycle enzymes, CO 2 and carbohydrate transport, and light reactions among many others. In addition, other areas which promise scope for improvement of C3 photosynthesis, such as mining natural genetic variations, mathematical modelling for identifying new targets, installing efficient carbon fixation and carbon concen- trating mechanisms have been touched upon. Briefly, this review intends to shed light on the recent advances in enhancing C3 photosynthesis for crop improvement. Introduction According to the World Food Summit held in 1996 at Rome, food security is defined as ‘when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life’. However, with a burgeoning population, decreasing arable land, stagnation in agricultural production, the erratic and extreme environmental changes due to global warming along with various biotic stresses, it becomes an overwhelming task to ensure complete food and nutrient security. Recent statistics reveal that over 870 million people are chronically undernour- ished in terms of dietary energy supply (FAO, 2012). It is estimated that global food production must increase 50% by 2030 and 70%–100% by the year 2050, to feed adequately a global population of around nine billion people (Covshoff and Hibberd, 2012; Long, 2012; Zhu et al., 2010a). Huge improve- ments in grain yield achieved in the past by the green revolution seem to be inadequate to feed the exponentially increasing global population, and the need for another quantum leap in agricul- tural productivity has never been more crucial. One fundamental component of plant productivity that has yet to be utilized to potential for increasing yield is photosynthesis. The time is at hand to employ our extensive knowledge of this fundamental process to improve crop productivity. Photosynthesis Life on earth requires a constant source of energy to fuel its activities. Photosynthesis provides this energy by converting light, normally from the sun into chemical energy of carbohydrates using CO 2 and water. Enhancing photosynthetic capacity of plants is a very promising approach to increase crop productivity. Moreover, because of its carbon sequestering ability, photosyn- thesis reduces the concentration of CO 2 in the atmosphere, the primary component of green house gases and therefore would help mitigate global warming (Ruan et al., 2012). The Calvin–Benson–Bassham cycle (CBB cycle/C3 photosynthe- sis) is used by majority of terrestrial plants for assimilation of CO 2 into organic matter and fixes 100 billion tons of carbon a year that constitutes 15% of the carbon in the atmosphere (Raines, 2011). The first stable compound formed in C3 photosynthesis is phosphoglycerate (3-PGA) and consists of three carbon atoms, hence the name ‘C3 cycle’. In C3 photosynthesis, mesophyll cells containing RuBisCO remain in direct contact with the intercellular air space that is connected to the outer environment via stomatal Please cite this article as: Singh, J., Pandey, P., James, D., Chandrasekhar, K., Achary, V.M.M., Kaul, T., Tripathy, B.C. and Reddy, M.K. (2014) Enhancing C3 photosynthesis: an outlook on feasible interventions for crop improvement. Plant Biotechnol. J., doi: 10.1111/pbi.12246 ª 2014 Society for Experimental Biology, Association of Applied Biologists and John Wiley & Sons Ltd 1 Plant Biotechnology Journal (2014), pp. 1–14 doi: 10.1111/pbi.12246