In-frame editing of transcription factor gene RDD1 to suppress miR166 recognition influences nutrient uptake, photosynthesis, and grain quality in rice

The transcription factor-encoding gene RDD1 increases the uptake of nutrient ions, photosynthetic activity under ambient and high CO(2) conditions, and grain productivity, and microRNA166 (miR166) regulates its transcript levels. This study found that CRISPR/Cas9 genome editing of rice plants to inhibit miR166–RDD1 transcript pairing (R1-Cas plants) increased RDD1 transcript levels, NH(4)(+) and PO(4)(3−) uptake, and photosynthetic activity under high CO(2) conditions in rice. However, the panicle weight of the R1-Cas plants decreased compared with the wild-type (WT) plants. Adversely, changes in environmental conditions, such as high CO(2) or high temperatures, showed insignificant differences in the panicle weight between the WT and R1-Cas plants despite a largely increased panicle weight observed in the transgenic RDD1-overexpressing plants. Moreover, both the R1-Cas and transgenic RDD1-overexpressing plants that were matured in a growth chamber demonstrated an improved grain appearance quality or a decrease in the number of chalky grains compared with the WT plants. These results suggest that the in-frame mutagenesis of RDD1 to suppress miR166–RDD1 transcript pairing contributes to the improved grain appearance of rice.