Genetic engineering to develop a two-celled type C4 rice

Melgar, R.J.; Karki, S.; Reyes, J.; Montecillo, F.A.; Realubit, C.M.; Lorenzana, G.; Dela Rosa, M.; Kamal, S.; Acoba, M.G.; Tapia, R.; Slamet Leodin, S.; Quick, P., International Rice Research Inst., DAPO Box 7777, Metro Manila . C4 Rice Center

Genetic engineering to develop a two-celled type C4 rice

2012

The world's population is projected to be 9 billion by 2050. Rice is the staple food of over half of the world's population and a predominant dietary energy source. In order to provide adequate food and nutrition in the future, rice yields need to increase by 60%. This could be achieved by converting the photosynthetic pathway of rice (C3) to the more efficient C4 type. This would increase rice yields while using resources (land, water, and fertilizer specifically nitrogen) more effectively. The aim is to genetically engineer a two-celled C4 photosynthetic shuttle in rice by expressing the classical enzymes of a NADP-ME C4 cycle in rice. To create prototype C4 rice, the authors are using Agrobacterium to introduce the genes of C4 pathway from maize into rice. Thirteen constructs to manipulate seven genes were generated and each has entered the transformation pipeline. Lines in which the authors have successfully over expressed C4 Phosphoenolpyruvate carboxylase (PEPC) and Pyruvate, orthophosphate dikinase (PPDK) genes from Zea mays are currently at the T3 stage, while T1 plants expressing NADP- Malate Dehydrogenase and NADP-Malic Enzyme genes are setting T2 seeds. To have an efficient C4 cycle in rice, some of the endogenous enzymes such as Rubisco and glycine decarboxylase have to be down regulated in mesophyll cells of rice. To achieve this, the authors are using artificial micro RNA construct. The authors are currently evaluating T1 and T2 lines for knock-down of Rubisco and Glycine Decarboxylase H subunit (GdcH). They have initiated transformation of C4 transporters into rice. Inter-crossing of these transgenic rice lines will be conducted for gene stacking which is expected to build in fundamental components of the C4 pathway in rice.

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