Functionality of soybean CBF/DREB1 transcription factors.

Soybean (Glycine max) is considered to be cold intolerant and is not able to significantly acclimate to cold/freezing stress. In most cold tolerant plants, the C-repeat/DRE Binding Factors (CBF/DREBs) are critical contributors to successful cold-responses; rapidly increasing following cold treatment and regulating the induction of many cold responsive genes. In soybean vegetative tissue, we found strong, transient accumulation of CBF transcripts in response to cold stress; however, the soybean transcripts of typical cold responsive genes (homologues to Arabidopsis genes such as dehydrins, ADH1, RAP2.1, and LEA14) were not significantly altered. Soybean CBFs were found to be functional, as when expressed constitutively in Arabidopsis they increased the levels of AtCOR47 and AtRD29a transcripts and increased freezing tolerance as measured by a decrease in leaf freezing damage and ion leakage. Furthermore the constitutive expression of GmDREB1A;2 and GmDREB1B;1 in Arabidopsis led to stronger up-regulation of downstream genes and more freezing tolerance than GmDREB1A;1, the gene whose transcript is the major contributor to total CBF/DREB1 transcripts in soybean. The inability for the soybean CBFs to significantly up regulate the soybean genes that contribute to cold tolerance is consistent with poor acclimation capability and the cold intolerance of soybean.