New genes for yield increase of Super Rice have been discovered

The super rice germplasm innovation team of China Rice Research Institute of Chinese Academy of Agricultural Sciences cooperated with the Institute of Genetics and Developmental Biology of Chinese Academy of Sciences to successfully isolate and clone an important gene GS2 which can significantly increase the yield of super rice from Zhejiang local large-grain variety "Bao Dazi". The relevant research results are published online in this year's latest issue of the internationally renowned journal Molecular Plant. The research is supported by the National Natural Science Foundation of China and the Ministry of Science and Technology.

It is reported that as the storage organ of assimilation products, the yield of rice seeds is the direct assessment index of agricultural production. In production, rice yield is mainly composed of effective panicles, grains per panicle and grain weight. Grain weight is generally expressed by 1000-grain weight, which is the comprehensive embodiment of grain length, grain width and grain thickness. In the process of long-term domestication of rice, due to the characteristics of large harvest index and easy processing, it gradually formed that the grain of cultured seeds was significantly larger than that of wild relatives. Therefore, in super-high-yield breeding, increasing 1000-grain weight to increase rice yield has been an effective means widely used by breeders.

In the 1990s, the research team obtained a copy of Zhejiang local large-grain variety "Bao Da Grain" from the National Rice Germplasm Resources Mid-term Bank. The plant is tall and strong, the spike is long and grain is large, and the 1000-grain weight is more than 48g. Through QTL (quantitative trait loci, which refers to the position of genes controlling quantitative traits in the genome) analysis and high-generation backcross population, a major grain type QTL gene GS2 was obtained on chromosome 2, which encodes a rice growth regulatory factor OsGRF4. The researchers found that a rare dominant mutation in the GS2 allele from "Bao Da Gu" occurred at the miR396c target, resulting in a significant increase in the expression of the gene, which promoted cell division and growth, and finally specifically increased ear length and grain size.

Through the field experiment of the near-isogenic lines bred by continuous backcross it was found that the GS2 dominant allele could significantly increase the rice yield while significantly increasing the panicle length and 1000-grain weight while the changes of other agronomic traits such as plant height and tiller were not obvious thus the harvest index was increased and the yield was finally increased. "Liangyoupeijiu" is the first two-line hybrid super rice variety in China, with a total planting area of more than 100 million mu all over the country. The GS2 dominant allele from "Baodagi" could increase the 1000-grain weight and plot yield of "Liangyoupeijiu" parent "9311" by more than 40% and 14%. After combining it with the "Peiai 64s" variety to form a hybrid rice, it can further increase the yield by 9.5% compared with the super rice "Liangyoupeijiu" variety. In addition, the researchers also found that the GS2 dominant gene was more in line with the production requirements in the heterozygous state, so combining the restorer lines containing the GS2 dominant allele with male sterile lines with excellent quality would be helpful to cultivate new super rice varieties with high yield.