The research team led by Dr. Liu Bin at Institute of Crop Sciences (ICS), CAAS discovered that a soybean (Glycine max) cryptochrome 2 (GmCRY2a) regulates leaf senescence, which is a life history trait regulated by light and photoperiods via previously unknown mechanisms. Cryptochromes are evolutionarily conserved flavoproteins that act as blue light receptors or intrinsic components of the circadian oscillator in plants and animals, but the molecular mechanisms of cryptochrome signal transduction remains poorly understood in plants.

This study found that GmCRY2a undergoes blue light-dependent interaction with the soybean bHLH transcription activator GmCIB3 that specifically interacts with the E-box (CANNTG) DNA sequences. Analyses of transgenic soybean plants expressing elevated or reduced level of the GmCRY2a or GmCIB3 protein demonstrate that GmCIB3 promotes leaf senescence, whereas GmCRY2a suppresses leaf senescence. Results of the gene expression and molecular interaction analyses support a hypothesis that GmCIB3 stimulates transcription of the senescence-associated gene WRKY53b and leaf senescence by interacting with the E box-containing promoter sequences of the WRKY53b chromatin, whereas GmCRY2a suppresses WRKY53b transcription and leaf senescence by interacting with GmCIB3 to inhibit its DNA-binding activity. These findings argue that the CIB-dependent transcriptional regulation is an evolutionarily conserved CRY-signaling mechanism in plants and this mechanism is opted in evolution to mediate light regulation of different aspects of plant development in different plant species.

The results were published online on the international journal The Plant Cell. 
The work is supported by National Science Foundation of China (NSFC).