Genomic Approaches to Photoperiodic Flowering Response in Soybean

Flowering response to changes in seasonal photoperiods is critical to environmental adaptation of crop plants. To understand the molecular mechanisms of photoperiodic flowering in soybean, we surveyed changes in gene expression in response to photoperiods by 1) transcriptome sequencing, and 2) qRT-PCR of flowering gene homologs, using G. max reference varieties, near-isogenic lines of E loci (E1, E2, E3, and E5), and a soybean ancestor, G. soja. E loci showed 3,397 differentially expressed genes (DEG) in all treatments, with the highest DEG in E2 (1,860), followed by E1 (1,651) and E3 (1,559). E loci responded differently to day-lengths and time points. GO term analysis showed enrichment of different functions in different E loci. Flowering gene homologs were enriched in DEG in E1, E2, and E3, but not in E5. Key flowering gene homologs in the photoperiod pathway, including GmCO and GmFT, showed a different expression pattern from that of Arabidopsis CO and FT, whereas genes in the circadian clocks and the vernalization pathways showed a similar expression pattern. The peak expressions of GmCO2a and GmCO2b overlap with that of GmFT, suggesting that they might be a regulator of GmFT. Regulatory interactions of flowering genes are being elucidated further using a co-expression-based network analysis.

To identify novel genes underlying photoperiodic flowering in soybean, we explored the G. soja genome. Our QTL mapping analysis identified previously unidentified flowering and maturation loci. Together, our work will provide essential information and genetic resources to develop superior germplasm that is adaptive to diverse photoperiods.