Natural variation at the soybean J locus improves adaptation to the tropics and enhances yield

Soybean is a major legume crop originating in temperate regions, and photoperiod responsiveness is a key factor in its latitudinal adaptation. Varieties from temperate regions introduced to lower latitudes mature early and have extremely low grain yields. Introduction of the long-juvenile (LJ) trait extends the vegetative phase and improves yield under short-day conditions, thereby enabling expansion of cultivation in tropical regions. Here we report the cloning and characterization of <i>J</i>, the major classical locus conferring the LJ trait, and identify <i>J</i> as the ortholog of <i>Arabidopsis thaliana EARLY FLOWERING 3</i> (<i>ELF3</i>). <i>J</i> depends genetically on the legume-specific flowering repressor<i> E1</i>, and <i>J</i> protein physically associates with the <i>E1</i> promoter to downregulate its transcription, relieving repression of two important<i> FLOWERING LOCUS T</i> (<i>FT</i>) genes and promoting flowering under short days. Our findings identify an important new component in flowering-time control in soybean and provide new insight into soybean adaptation to tropical regions.