A Dual-localized Fructose Bisphosphate Aldolase is Essential for Chloroplast Development and Carbon Metabolism in Rice

Fructose-1,6-bisphosphate aldolase (FBA) stands as a pivotal enzyme involved within the Calvin cycle and glycolytic pathways in bacteria and higher plants, but the specific function of OsFBA in rice is still unclear. Here, we identified a chloroplast and mitochondria dual-localized FBA protein, OsFBA1, in rice. Experimental evidence showed that the functionally deficient osfba1 mutants featured a notable decline in chlorophyll content, photosynthetic rate, and severe growth impediment by the three-leaf stage, leading to eventual plant demise. Up-regulation of photosynthetic-pathway genes in the osfba1 mutants indicated the essential role of OsFBA1 in chloroplast development and suggested a compensatory mechanism of other genes in the process. Furthermore, the absence of OsFBA1 impaired the carbon assimilation in young rice seedlings, and supplying exogenous glucose could partially sustain the survival of osfba1 mutant for a few more days. Pathway-specific metabolomics analysis revealed a systemic change of metabolites in the glycolytic pathway, and consequential carbohydrates accumulation due to OsFBA1 disruption. Transcriptomics profiling corroborated the expression changes of photosynthesis, and carbon metabolism pathway genes. We further demonstrated that OsFBA1 serves as the primary FBA enzyme governing energy generation, photosynthesis and carbon metabolism. These results prove that OsFBA1 is an essential core gene in supporting the life cycle of rice, its expression has to be tightly regulated.