Addressing the escalating global food crisis necessitates innovative approaches in agricultural biotechnology. Engineering C4 photosynthetic traits into C3 crops like rice, a staple food source for billions worldwide, holds significant potential for enhancing yield and ensuring sustainable food security. Here, we present our ongoing research efforts towards realizing this ambitious goal, focussing on engineering the C4 metabolic pathway in rice. Building upon previous successes in the C4 Rice project, which introduced a partial NADP-malic enzyme type C4 pathway into rice1, our current efforts focus on complementing this minimal cycle by enhancing metabolite transport between mesophyll and bundle sheath cells to achieve its full functionality. To facilitate a unidirectional flow of metabolites through the C4 pathway, we introduced two constructs containing five key metabolic enzymes and seven membrane transporters, driven by cell-specific promoters, into rice (Oryza sativa spp. japonica cultivar Kitaake). Analysis of photosynthesis and growth in transgenic rice plants harbouring both constructs revealed correlations between phenotype and transgene expression levels. Notably, overexpression of certain transporters led to a slow-growth and chlorotic phenotype, possibly due to imbalances in carbon and nitrogen metabolism transport capacities, considering the dual roles of these transporters in these pathways2,3. Our ongoing investigation into the correlation between transgene expression levels, metabolite profiles, and physiological characteristics aims to deepen our understanding of the underlying mechanisms contributing to these deleterious phenotypes and to inform future engineering efforts.