Positional cloning and characterization reveal the molecular basis for soybean maturity locus E1 that regulates photoperiodic flowering
Zhengjun Xi^1,2, 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.
Corresponding Author：Tel: (+86451) 8750 1708; Fax: (+86451)8660 3736; E-mail: xiazhj@neigaehrb.ac.cn

Abstract
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