Abstract
CONSTANS (CO) plays a central role in photoperiodic flowering control of plants. However, much remains unknown about the function of the CO gene family in soybean and the molecular mechanisms underlying short-day photoperiodic flowering of soybean. We identified 26 CO homologs (GmCOLs) in the soybean genome, many of them previously unreported. Phylogenic analysis classified GmCOLs into three clades conserved among flowering plants. Two homeologous pairs in Clade I, GmCOL1a/GmCOL1b and GmCOL2a/GmCOL2b, showed the highest sequence similarity to Arabidopsis CO. The mRNA abundance of GmCOL1a and GmCOL1b exhibited a strong diurnal rhythm under flowering-inductive short days and peaked at dawn, which coincided with the rise of GmFT5a expression. In contrast, the mRNA abundance of GmCOL2a and GmCOL2b was extremely low. Our transgenic study demonstrated that GmCOL1a, GmCOL1b, GmCOL2a and GmCOL2b fully complemented the late flowering effect of the co-1 mutant in Arabidopsis. Together, these results indicate that GmCOL1a and GmCOL1b are potential inducers of flowering in soybean. Our data also indicate rapid regulatory divergence between GmCOL1a/GmCOL1b and GmCOL2a/GmCOL2b but conservation of their protein function. Dynamic evolution of GmCOL regulatory mechanisms may underlie the evolution of photoperiodic signaling in soybean.
Highlights
Soybean, one of the most important sources of protein and oil in the world, flowers in response to a photoperiod change from long day to short day at the summer solstice [1]
Each GmCOL was assigned a name based on its homology level to Arabidopsis CO and COLs, with a designation of a or b for homeologous pairs originating from the most recent duplication event (e.g. GmCOL1a and GmCOL1b)
We identified 26 COL homologs from the soybean genome and characterized their photoperiod response in mRNA accumulation, sequence divergence and protein function
Summary
One of the most important sources of protein and oil in the world, flowers in response to a photoperiod change from long day to short day at the summer solstice [1]. Despite this crop’s agronomic importance, the molecular basis of the photoperiodic flowering response in soybean remains only partially characterized. The causal genes for four of these maturity loci, E1– E4, were recently identified. A transcription factor containing a plantspecific B3 domain was recently cloned as the causal gene of E1 [10]
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