AUTHOR=Zhu Jianghui , Takeshima Ryoma , Harigai Kohei , Xu Meilan , Kong Fanjiang , Liu Baohui , Kanazawa Akira , Yamada Tetsuya , Abe Jun 

TITLE=Loss of Function of the E1-Like-b Gene Associates With Early Flowering Under Long-Day Conditions in Soybean

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01867

DOI=10.3389/fpls.2018.01867

ISSN=1664-462X

ABSTRACT=<p>Photoperiod response of flowering determines plant adaptation to different latitudes. Soybean, a short-day plant, has gained the ability to flower under long-day conditions during the growing season at higher latitudes, mainly through dysfunction of <italic>phytochrome A</italic> genes (<italic>E3</italic> and <italic>E4</italic>) and the floral repressor <italic>E1</italic>. In this study, we identified a novel molecular genetic basis of photoperiod insensitivity in Far-Eastern Russian soybean cultivars. By testcrossing these cultivars with a Canadian cultivar Harosoy near-isogenic line for a recessive <italic>e3</italic> allele, followed by association tests and fine mapping, we determined that the insensitivity was inherited as a single recessive gene located in an 842-kb interval in the pericentromeric region of chromosome 4, where <italic>E1-Like b</italic> (<italic>E1Lb</italic>), a homoeolog of <italic>E1</italic>, is located. Sequencing analysis detected a single-nucleotide deletion in the coding sequence of the gene in insensitive cultivars, which generated a premature stop codon. Near-isogenic lines (NILs) for the loss-of-function allele (designated <italic>e1lb</italic>) exhibited upregulated expression of soybean <italic>FLOWERING LOCUS T</italic> (<italic>FT</italic>) orthologs, <italic>FT2a</italic> and <italic>FT5a</italic>, and flowered earlier than those for <italic>E1Lb</italic> under long-day conditions in both the <italic>e3</italic>/<italic>E4</italic> and <italic>E3</italic>/<italic>E4</italic> genetic backgrounds. These NILs further lacked the inhibitory effect on flowering by far-red light–enriched long-day conditions, which is mediated by <italic>E4</italic>, but not that of red-light–enriched long-day conditions, which is mediated by <italic>E3</italic>. These findings suggest that <italic>E1Lb</italic> retards flowering under long-day conditions by repressing the expression of <italic>FT2a</italic> and <italic>FT5a</italic> independently of <italic>E1</italic>. This loss-of-function allele can be used as a new resource in breeding of photoperiod-insensitive cultivars, and may improve our understanding of the function of the <italic>E1</italic> family genes in the photoperiod responses of flowering in soybean.</p>