Research On The Molecular Mechanism Of BIC2 Inhibiting Blue Light Photoreceptor CRY2 Activity In Arabidopsis Thaliana

As a rich natural resource,light not only provides the energy for plant growth,but also can be used as a signal to regulate various life activities of plants,such as the photoperiod,photomorphogenesis,stomata opening,and seed germination.The input of light signals is mediated by different photoreceptors which interact with other proteins in different signaling pathways to integrate and output light signals,and consequently trigger various physiological effects.Cryptochrome?CRY?,a canonical one,is a blue light photoreceptor that is responsible for sensing blue light.Chromophore FAD????lavin ???denine ???inucleotide?molecule in cryptochrome is responsible for sensing blue light signals.After the FAD molecule senses blue light,consecutive photoreduction reactions occur to lead to conformational changes of the CRY,causing transition from the inactive form to the activated form via homo-oligomerization and phosphorylation.Active CRY interacts with various downstream regulatory proteins(such as CIBs?CUL4^COP1-SPAs?PIFs)to initiate signal transductions.Continuous light activation is detrimental to plant growth and the process needs to be regulated.In Arabidopsis thaliana,BIC????lue-light ???nhibitor of ???ryptochromes?works with CRY2 protein during activation to inhibit the activity of CRY2 and play a negative regulatory role.However,its molecular mechanism is not clear.In this thesis,we sought to determine the crystal structure of the CRY2N-BIC2complex.In vitro molecular sieve co-elution experiments showed that BIC protein could not only inhibit the oligomerization of CRY2,but also prevented CRY2 from binding to downstream transcription factor CIB1????ryptochrome-???nteracting ???asic-helix-loop-helix 1?.In the further determination of the redox potential,we found that the CRY2 alone is unstable,and prone to be precipitated during the reaction,which severely affects measurement.Comparably,the CRY2?N?-BIC2 complex reaction sample was stable,suggesting that the protein precipitation was related to the conformational changes and CRY2 was tied down by BIC2 and its conformational change was impeded simultaneously.These results showed that BIC2 inhibits the physiological activity of CRY2 by inhibiting CRY2 oligomerization and conformational change,abolishing CRY2 binding to downstream transcription factors.