Improving Soybean Yield and Quality by Optimizing Nodulation

In soybean breeding, there is an insurmountable negative correlation between yield and protein. In the past, soybean breeding aimed at yield often resulted in a significant decrease in protein content, which became a bottleneck that plagued the breeding of high-yielding, high-protein and high-oil soybeans. At the same time, soybeans can fix air nitrogen through nodulation and are an environmentally friendly crop. However, the yield of super-nodulation soybeans discovered in the past all decreased due to carbon and nitrogen imbalance, leading to the inherent thinking that "high nodulation in soybeans will reduce yield". Therefore, genetic improvement of biological nitrogen fixation is generally ignored in breeding.

On May 9, 2024, Yuefeng Guan's research group from Guangzhou University and his collaborators published a research paper titled "Genetically optimizing soybean nodulation improves yield and protein content" in Nature Plants. They precisely controlled the number of root nodules through gene editing to achieve efficient nitrogen fixation with carbon and nitrogen balance, thus significantly increasing soybean yield and protein content under field planting conditions. This study therefore proposes new ideas for precision breeding that optimize nodulation and nitrogen fixation to promote high yield and high quality.

This study created various soybean mutants (nin-4m, ric1b/2b, ric1a/2a, ric-6m and nark) with varying degrees of nodule number through gene editing. It was found that the biomass of the super-nodulated soybean mutants ric-6m and nark was reduced, while the biomass of the ric1a/2a mutant with doubled root nodules was significantly increased. Isotope tracing and other experiments show that the appropriate increase in the number of root nodules in ric1a/2a not only increases biological nitrogen fixation, but also promotes chlorophyll content through nitrogen, enhances soybean photosynthetic efficiency, and ultimately achieves synergistic promotion of carbon and nitrogen. The appropriately increased root nodules in ric1a/2a did not consume too much carbon source like the hypernodulation mutant, thus maintaining the carbon and nitrogen balance. The author has conducted multi-site field experiments for many years in Fujian, Hebei and other places in China. Compared with the chassis national approval variety Huachun 6, the plot yield of ric1a/2a has significantly increased by more than 10-20%, while the protein content has steadily increased by 1-2 percentage points without significantly reducing the oil content. This is attributed to the synergistic increase in carbon and nitrogen sources transported to seeds in ric1a/2a, thus achieving biological breeding that synergistically increases yield and protein. Optimizing soybean nodulation and nitrogen fixation through biological breeding methods such as gene editing is expected to become an important way to improve soybean yield and quality.

Reference

1. Zhong,X., et al. Genetically optimizing soybean nodulation improves yield and protein content. Nat Plants. 2024, 10(5): 736-742.

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