Expression of flowering-time genes in soybean E1 near-isogenic lines under short and long day conditions

Control of soybean flowering time is important for geographic adaptation and maximizing yield. Plant breeders have identified a series of genes (E genes) that condition time to flowering; however, the molecular basis in the control of flowering by these E genes, in conjunction with canonical flowering-time genes, has not been studied. Time to flowering in near-isogenic lines (NILs) at the E1 locus was tested using a reciprocal transfer experiment under short day (SD) and long day (LD) conditions. Beginning 8 days after planting, three plant samples were harvested every 3 h for a 48-h period. RNA was isolated from these plants, and RNA samples were pooled for each line and each time period for cDNA synthesis. RT-PCR analysis was performed using primers synthesized for a number of putative flowering-time genes based on homology of soybean EST and genomic sequences to Arabidopsis genes. The results of the reciprocal transfer experiment suggest that the pre-inductive photoperiod-sensitive phase of the E1 NILs responsible for inducing flowering is perceived as early as 5-7-day post-planting. No gene expression differences were found between the E1 and e1 NILs, suggesting that the E1 gene does not directly affect the flowering-time genes during the time period tested; however, differences were observed in gene expression between SD and LD treatments for the putative soybean TOC1, CO, and FT genes. The gene expression results in this study were similar to those of flowering-time genes found in other SD species, suggesting that the selected genes correspond to the soybean flowering-time orthologs.