New gene discovered that boosts super rice yields

The super rice germplasm innovation team of the China National Rice Research Institute under the Chinese Academy of Agricultural Sciences, in collaboration with the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences and other institutions, successfully isolated and cloned from the Zhejiang local large-grain variety "Baodali" an important gene, GS2, that can significantly increase super rice yields. The related research results were published online in the latest issue of this year of the internationally renowned journal Molecular Plant. The research was funded by the National Natural Science Foundation of China and the Ministry of Science and Technology.

It is reported that the rice seed, as a storage organ for assimilates, has a harvest yield that is a direct assessment indicator of agricultural production. In production, rice yield is mainly composed of three elements: the number of effective panicles, the number of grains per panicle and grain weight. Grain weight is generally expressed as 1000-grain weight, and is a comprehensive reflection of grain length, grain width and grain thickness. During the long-term domestication of rice, due to characteristics such as a large harvest index and ease of processing, the trait gradually formed whereby the grains of cultivated species are clearly larger than those of wild relatives. Therefore, in super-high-yield breeding, increasing the 1000-grain weight to raise rice yield has already become an effective means commonly used by breeders.

In the 1990s, the research team obtained from the National Medium-term Genebank for Rice Germplasm Resources a Zhejiang local large-grain variety, "Baodali", whose plants are tall and robust, with long panicles and large grains, and a 1000-grain weight of more than 48 grams. Through QTL (quantitative trait locus, referring to the position in the genome of a gene controlling a quantitative trait) analysis and high-generation backcross populations, a major grain-type QTL gene, GS2, was obtained on chromosome 2. This gene encodes a rice growth regulator, OsGRF4. The researchers found that the GS2 allele from "Baodali" has a rare dominant mutation at the miR396c target site, causing a significant increase in the expression of this gene, thereby promoting cell division and growth, and ultimately specifically increasing panicle length and grain size.

Field trials of near-isogenic lines developed through continuous backcrossing found that this GS2 dominant allele can significantly increase rice yield, specifically manifesting as a significant increase in panicle length and 1000-grain weight, while changes in other agronomic traits such as plant height and tillering were not obvious, thereby increasing the harvest index and ultimately increasing yield. "Liangyoupeijiu" is China's first two-line hybrid super rice variety, and its cumulative promoted planting area across the country has exceeded 100 million mu. The GS2 dominant allele from "Baodali" can increase the 1000-grain weight of "Liangyoupeijiu" parent "9311" by more than 40% and the plot yield by more than 14%. And after combining it with the variety "Pei'ai 64S" to form a hybrid rice, it can further increase yield by 9.5% compared with the super rice variety "Liangyoupeijiu". In addition, the researchers also found that this GS2 dominant gene in the heterozygous state better meets production needs. Therefore, combining a restorer line containing this GS2 dominant allele with an excellent-quality sterile line will help breed new high-yield super rice varieties.