Fine-tuning flowering time via genome editing of upstream open reading frames of Heading date 2 in rice

Abstract Flowering time of rice (Oryza sativa L.) is among the most important agronomic traits for region adaptation and grain yield.In the process of rice breeding, efficient and slightly modulating the flowering time of an elite cultivar would be more popular with breeder. Hence, we focus on slightly increasing the expression of flowering repressors by CRISPR/Cas9 genome editing system. It was predicated there were three uORFs in 5' leader sequence of Hd2.By editing Hd2 uORFs, we got four homozygous mutant lines and phenotypic analysis showed their heading date delay by 4.6–11.2 days relative to wide type SJ2.The mutation do not affect transcript level of Hd2, but improve translation of a downstream Hd2 pORF. In summary, we developed a efficient approach for delaying rice heading date based on editing uORF region of flowering repressor, which is time and labor saving compared to traditional breeding. In future, uORF of other flowering time related genes, including flowering promoter and flowering repressor genes, can also be used as targets to fine-tune the flowering time of varieties.