Grain size is a key agronomic trait that determines the yield in plants. Regulation of grain size by brassinosteroids (BRs) in rice has been widely reported. However, the relationship between the BR signaling pathway and grain size still requires further study. Here, we isolated a rice mutant, named small grain2 (sg2), which displayed smaller grain and a semi-dwarf phenotype. The decreased grain size was caused by repressed cell expansion in spikelet hulls of the sg2 mutant. Using map-based cloning combined with a MutMap approach, we cloned SG2, which encodes a plant-specific protein with a ribonuclease H-like domain. SG2 is a positive regulator downstream of GLYCOGEN SYNTHASE KINASE2 (GSK2) in response to BR signaling, and its mutation causes insensitivity to exogenous BR treatment. Genetical and biochemical analysis showed that GSK2 interacts with and phosphorylates SG2. We further found that BRs enhance the accumulation of SG2 in the nucleus, and subcellular distribution of SG2 is regulated by GSK2 kinase activity. In addition, Oryza sativa OVATE family protein 19 (OsOFP19), a negative regulator of grain shape, interacts with SG2 and plays an antagonistic role with SG2 in controlling gene expression and grain size. Our results indicated that SG2 is a new component of GSK2-related BR signaling response and regulates grain size by interacting with OsOFP19.

Pre-harvest sprouting (PHS) in cereal crops, is a universal phenomenon that affects grain yield and quality (Tai et al. 2021). Breeders use different methods to strengthen seed dormancy to prevent PHS including genome editing. Abscisic acid is one of the phytohormones that promote seed dormancy. ABA8ox genes encode abscisic acid 8' hydroxylase (ABA8OX) which determines the level of ABA content by catabolizing ABA (Vallabhaneni and Wurtzel 2010). Three genes in rice encode ABA8' hydroxylases, namely OsABA8ox1 (LOC_Os02g47470), OsABA8ox2 (LOC_Os08g36860) and OsABA8ox3 (LOC_Os09g28390) (Kushiro et al. 2004;Cai et al. 2015;Zhang et al. 2020). Each gene is expressed in different tissues of rice. Key MessageKnock out OsABA8ox helps improve pre-harvest spouting resistance and do not effect rice yield.

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Storage tolerance is an important agronomic character in rice (Oryza sativa L.). Lipoxygenase (LOX) is a key enzyme in lipid metabolism, and its activity directly affects the rate of aging in rice. Here, lipoxygenase gene OsLOX1 was edited by CRISPR/Cas9 in Ningjing 4. We found that OsLOX1 knock-out can delay seed vigor loss, lipid metabolism and quality deterioration after aging. In addition, combining the transcriptome analysis, we could conclude that OsLOX1 affected the transcription of multiple genes during storage, and was involved in seed storage tolerance by regulating lipid metabolism and antioxidant pathways such as phosphatase and acetaldehyde dehydrogenase. By knocking out LOX1 gene, a new rice material with high vigor and no exogenous vector skeleton was bred to improve the storage tolerance of seeds and provide material support for rice breeding in China.

Pre-harvest sprouting (PHS) in cereal crops, is a universal phenomenon that affects grain yield and quality (Tai et al. 2021). Breeders use different methods to strengthen seed dormancy to prevent PHS including genome editing. Abscisic acid is one of the phytohormones that promote seed dormancy. ABA8ox genes encode abscisic acid 8’ hydroxylase (ABA8OX) which determines the level of ABA content by catabolizing ABA (Vallabhaneni and Wurtzel 2010). Three genes in rice encode ABA8’ hydroxylases, namely OsABA8ox1 (LOC_Os02g47470), OsABA8ox2 (LOC_Os08g36860) and OsABA8ox3 (LOC_Os09g28390) (Kushiro et al. 2004; Cai et al. 2015; Zhang et al. 2020). Each gene is expressed in different tissues of rice.