Double Mutation of Days to Heading 2 and CONSTANS 3 Improves Agronomic Performance of Japonica Rice under Short Daylight Conditions in Southern China

Some progress has been made in understanding the pathways related to rice heading, but their applications to breeding japonica rice varieties adapted to grow in low-latitude areas (“indica to japonica”) are limited. We edited eight adaptation-related genes via a lab-established CRISPR/Cas9 system in a japonica variety, Shennong265 (SN265). All T(0) plants and their progeny bearing random mutation permutations were planted in southern China and screened for changes in heading date. We found that the double mutant of Days to heading 2 (DTH2) and CONSTANS 3 (OsCO3) (dth2-osco3), two CONSTANS-like (COL) genes, showed significantly delayed heading under both short-day (SD) and long-day (LD) conditions in Guangzhou and manifested great yield increase under SD conditions. We further demonstrated that the heading-related Hd3a-OsMADS14 pathway was down-regulated in the dth2-osco3 mutant lines. The editing of the COL genes DTH2 and OsCO3 greatly improves the agronomic performance of japonica rice in Southern China.