Location: Forage-animal Production ResearchTitle: Expression of Flowering-Time Genes in Soybean E1 Near-isogenic Lines Under Short and Long Day Conditions Author
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2010
Publication Date: 1/22/2010
Citation: Thakare, D., Kumudini, S., Dinkins, R.D. 2010. Expression of Flowering-Time Genes in Soybean E1 Near-isogenic Lines Under Short and Long Day Conditions. Planta (2010). 231:951-963. Interpretive Summary: Control of flowering time is important for geographic adaptation and maximizing yield. Very little is known about the genes that condition flowering response in legumes. Soybean is an excellent model system for legume research as the genome sequence has recently been released. Using gene sequences obtained from the model plants species Arabidopsis, putative soybean orthologues were identified in the soybean expressed sequence tag (EST) and genomic databases. Plant samples were isolated every three hours for a 48 hour period from two soybean near-isogenic lines (differing at the E1 locus that conditions differential response to day length) under a short day and long day treatment. Expression profiles of the genes was tested using reverse transcription-polymerase chain reaction (RT-PCR) procedures. All of the selected putative orthologues showed the expected diurnal cycling in expression, as would be expected from flowering time genes. No differences in expression in any of the genes was observed between the two near-isogenic lines. Comparison of the day length treatments resulted in the expected expression differences, based on the Arabidopsis model. These results suggest that we have identified the soybean orthologues for a number of the flowering time genes in soybean. These results will allow for further refinement of conditions to determine the effect of differing light treatments, and soybean genotypes, and to better characterize the molecular basis of flowering response in legumes.
Technical Abstract: 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 been studied. The E-gene near-isogenic lines (NILs) provide an excellent model system for studying flowering pathway genes in soybean. Time to flowering for the E1 gene NILs in the Harosoy background [OT89-5 (e1) and OT93-26 (E1)] was tested using a reciprocal transfer experiment under short day (SD: 12hr day/12hr dark) and long day (LD: 20hr day/4hr dark) conditions. Beginning eight days after planting, three plant samples were harvested every three hours for a 48 hour 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 d 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. The gene expression results in this study were similar to those of flowering-time genes found in other species, suggesting that the selected genes correspond to the soybean flowering-time orthologues.