Positional cloning and characterization reveal the molecular basis for soybean maturity locus E1 that regulates photoperiodic flowering
Zhengjun Xi1,2, Satoshi Watanabe2, Tetsuya Yamada3, Yasutaka Tsubokura2, Hiroko Nakashima4, Hong Zhai1, Toyoaki Anai4, Toshimasa Yamazaki5, Shixiang Lü1, Hongyan Wu1, Kyuya Harad2
1Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin 150081, China;
2Soybean Applied Genomics Research Unit, National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan;
3Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan;
4Faculty of Agriculture, Saga University, Saga 840-8502, Japan;
5Biomolecular Research Unit, National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan.
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The maturity locus E1 has a large impact on flowering time in soybean, but the molecular basis for the E1 locus is largely unknown. Through positional cloning, we delimited the E1 locus to a 17.4-kb region containing an intron-free gene (E1). The E1 protein contains a putative bipartite nuclear localization signal and a region distantly related to B3 domain. In the recessive allele, a nonsynonymous substitution occurred in the putative nuclear localization signal, leading to the loss of localization specificity of the E1 protein and earlier flowering. E1 expression was significantly suppressed under short-day conditions and showed a bimodal diurnal pattern under long-day conditions, suggesting its response to photoperiod and its dominant effect induced by long day length. When a functional E1 gene was transformed into the early-flowering cultivar Kariyutaka with low E1 expression, transgenic plants carrying exogenous E1 displayed late flowering. Furthermore, the transcript abundance of E1 was negatively correlated with that of GmFT2a and GmFT5a, homologues of FLOWERING LOCUS T that promote flowering. The molecular identification of the maturity locus E1 will contribute to our understanding of the molecular mechanisms by which a short-day plant regulates flowering time and maturity.
Key Words: flowering time; maturity; E1; photoperiodism; positional cloning