How did "Mo" non-soybean become more abundant? Scientists found the key gene for increasing soybean yield with molybdenum fertilizer!

On November 22, 2023, the international authoritative botanical journal "Contemporary Biology" published online a research paper completed by Chao Daiyin's research group at the Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences and Tian Zhixi's research group at the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences. Through whole-genome association analysis, the study successfully cloned two key genes, GmMOT1.1 and GmMOT1.2, that regulate the natural variation of molybdenum content in soybean seeds. The results showed that these two genes increase soybean yield by promoting molybdenum-dependent auxin synthesis in soybean leaves, increasing leaf photosynthetic area. In addition, the study also found that these two genes have 5 haplotypes, and the geographical distribution of these haplotypes is closely related to soil pH, which can provide guiding molecular markers for customized breeding of soybeans that adapt to different soil types.

Molybdenum (Mo) is an indispensable trace element for plant growth, and it plays an important role in the growth processes of multiple organisms. For legumes, molybdenum fertilizer is particularly important. In the process of agricultural production, it is often necessary to apply foliar molybdenum fertilizer to improve the production potential of legumes. It is generally believed that the extremely high demand of legumes for molybdenum fertilizer is related to the high demand for molybdenum in the biological nitrogen fixation process of legumes. However, this theory conflicts with the need to spread molybdenum fertilizer on the leaves in production, because nodule nitrogen fixation occurs in the roots, but there are no reports of mineral nutrients being transported from leaves to roots in plants. Therefore, there may be unknown mechanisms for the reason why foliar molybdenum fertilizer promotes production.

Soybean is one of the most important crops for human beings and the main source of protein and oil. Its yield is related to food security and national security. However, people still don't know whether there are natural variations in the ability to absorb and utilize molybdenum between different soybean varieties, how these variations affect soybean production, and how to utilize these variations.

Using ionomics and genome-wide association analysis, researchers cloned two genes, GmMOT1.1 and GmMOT1.2, that regulate natural variation in soybean molybdenum content. Further analysis revealed that natural soybean lines contain five major haplotypes, of which the fifth haplotype had the highest expression level and molybdenum transport capacity in soybeans, while haplotype 4 had the lowest expression level and molybdenum transport capacity. A series of genetic and molecular experiments showed that GmMOT1.1 and GmMOT1.2 are involved in the absorption of molybdenum by soybean roots and the transport of molybdenum from the aboveground parts by the roots. When the functions of GmMOT1.1 and GmMOT1.2 were reduced, the molybdenum content and yield of the mutants were significantly reduced, while the enhancement of GmMOT1.1 could significantly increase the molybdenum content and soybean yield. Therefore, the two genes regulate the molybdenum content in the aboveground part of soybeans and further affect soybean yield.

Interestingly, GmMOT1.1 and GmMOT1.2 did not affect the nitrogen fixation ability of nodules, nor did they affect other nitrogen assimilation processes. Surprisingly, the auxin content of leaves changed significantly in mutants and overexpression plants of GmMOT1.1 and GmMOT1.2, with the auxin content of mutant leaves significantly reduced and the auxin content of overexpression strains increased. Further studies have shown that there is a molybdenum-binding aldehyde oxidase in soybean leaves, which can catalyze the synthesis of indole-3-acetaldehyde into auxin indole-3-acetic acid, but the catalytic activity depends on the molybdenum content. Therefore, when the functions of GmMOT1.1 and GmMOT1.2 become stronger, the molybdenum content of leaves increases, thereby promoting the synthesis of auxin and leaf growth, thereby increasing soybean yield. This result also explains why soybean yield can be promoted in agriculture by directly spraying molybdenum fertilizer on leaves.

In addition, the study also found that the distribution of different haplotypes of the two genes in different planting areas in China is closely related to soil pH. The haplotype with strong functions is mainly distributed in acidic low-molybdenum soil areas, while the haplotype with weak functions tends to be distributed in alkaline high-molybdenum soil areas, indicating that both have been artificially selected. This result shows that these two genes can be used to design molecular markers for the cultivation of customized high-yield soybean varieties that adapt to soils of different pH values.

This study revealed the genetic mechanism of natural variation in molybdenum content in soybean seeds, clarified the principle of molybdenum fertilizer in legume leaves to promote yield, and discovered molecular markers for customized soybean breeding based on soil pH, providing a strong scientific basis for further optimizing soybean planting and breeding strategies and cultivating nutritionally efficient soybean varieties.