Approaches to Enhance Photosynthetic Capacity in Crops

Enhancing photosynthetic capacity of both C3 and C4 crops is one of the means that may translate to improved yield potential and/or protect yield or abiotic stress conditions. As a means to explore this approach, we are exploring the expression of an inorganic carbon transporter B (ictB), from cyanobacteria Synechococcus sp. and sedoheptolose-1, 7-bisphosphatese (SBPase) from tomato which were previously shown to increase photosynthesis in transgenic plants. A total of five constructs for each crop with codon-optimized versions of both genes were assembled and used for Agrobacterium-mediated transformation of soybeans and wheat (C3) and sorghum (C4). These constructs either harboured individual ictB with or without small pea small subunit of Rubisco transit peptide (TP) to target protein to the plastid, SBPase or both genes in a stack. ictB gene in both soybean and wheat are constitutively expressed under 35S CaMV promoter while SBPase is under the control of pea Rbcs promoter. Additionally, all constructs used in sorghum transformation were under the control of pea Rbcs promoters. Molecular analysis of transgenic events carrying these genes show stable integration and expression in their progenies. In addition, phenotypic analysis of transgenic soybean events overexpressing stacked genes with or without TP and TP-ictB alone show improved photosynthesis during vegetative and reproductive stages under greenhouse conditions. Furthermore, transgenic sorghum overexpressing both ictB and SBPase in stack showed improved photosynthesis compared to wild type under salt stress.  Results indicated that overexpression of ictB and SBPase have the potential to increase photosynthetic capacity in soybean and sorghum.