Co-silencing E1 and its homologs in an extremely late-maturing soybean cultivar confers super-early maturity and adaptation to high-latitude short-season regions

Soybean (Glycine max (L.) Merr.), a typical short-day plant, is sensitive to photoperiod, which limits the geographical range for its cultivation. In the flowering pathway regulated by photoperiod, E1, a flowering inhibitor in soybean, plays the dominant role in flowering time regulation. Two E1 homologs, E1-like-a (E1La) and E1-like-b (E1Lb), play overlapping or redundant roles in conjunction with E1. In the present study, E1 and E1La/b were simultaneously silenced via RNA interference (RNAi) in Zigongdongdou (ZGDD), an extremely late-flowering soybean landrace from southern China. As a result, RNAi lines showed a much earlier-flowering phenotype and obvious photoperiod insensitivity compared with wild-type (WT) plants. In RNAi transgenic plants, the expression levels of flowering inhibitor GmFT4 and flowering promoters GmFT2a/GmFT5a were significantly down- and up-regulated, respectively. Further, the maturity group (MG) of the RNAi lines was reduced from WT ZGDD's MG VIII (extremely late-maturity) to MG 000 (super-early maturity), which can even grow in the northernmost village of China located at a latitude of 53.5°N. Our study confirms that E1 and E1La/b can negatively regulate flowering time in soybean. The RNAi lines generated in this study, with early flowering and maturity traits, can serve as valuable materials and a technical foundation for breeding soybeans that are adapted to high-latitude short-season regions.