Rice Transcriptomics Reveal the Genetic Determinants of An In Planta Photorespiratory Bypass: a Novel Way to Increase Biomass in C3 Plants

Developing C₄ rice is one of the global research challenges for yield improvement. In the optimal environment, the key difference between C₃ and C₄ plants with reference to biomass accumulation is photorespiration. Photorespiration is important for a plant’s survival. In spite of the high energy cost and carbon loss, diversion of a significant part of carbon from photorespiration to enrich CO₂ concentration (preventing carbon loss) was opted for. Installation of photorespiratory bypasses was reported to improve biomass and yield in C₃ plants. The contribution of non-foliar photosynthesis to yield improvement was well documented. However, its underlying genetic differences, when compared to foliar photosynthesis, are a research gap. In three rice genotypes (APO, BAM4234, and CROSSA), we compared the expression levels (for genes associated with photosynthesis and photorespiration) between the photosynthetic non-foliar (3–5-day old developing grains and peduncle) and foliar (flag leaf) organs to understand their differential expression pattern using an RNA-seq approach. Significant downregulation of the genes of photorespiration was observed in non-foliar photosynthetic tissue (3–5 dpa old developing grains) when compared to the flag leaves. Simultaneously, our study also revealed significant upregulation of the chloroplastic pyruvate dehydrogenase (cpPDC, BGIOSGA015796) gene in developing grains, when compared to the flag leaf, in all three genotypes. The occurrence of an in planta photorespiratory bypass in the photosynthetic tissues of the developing grains in rice is proposed. Enhanced expression levels for the cpPdc gene in the foliar tissues will potentially install a photorespiratory bypass for enhanced biomass accumulation and thereby yield.