Functional Analysis Of Wheat TaCKB4 In Photomorphogenesis And Salt Stress

The growth and development of plants are affected by light,temperature,drought and other environmental factors,which can affect the growth of plants either individually or through the formation of a complex and orderly regulatory network.We previously identified two blue light and salt responsive genes from wheat introgression line SR3,GBF transcriptional factor TaGBF1 and its putative target CKII kinase TaCKB4.TaGBFl promoted blue light mediated photomorphogenesis,while TaCKB4 inhibited blue light mediated photomorphogenesis in Arabidopsis.On the other hand,both TaGBFl and TaCKB4 reduced the tolerance to salt during germination.This paper further analyzed the function of TaCKB4 in wheat photomorphogenesis and salt stress response,and the relationship between TaCKB4 and TaGBFl.Under white and blue light,in comparison with wildtype,the length of coleoptile of wheat TaCKB4 overexpression lines was significantly increased,and the increase appeared more drastically under blue light,while no difference was found under red light.This indicated that TaCKB4 also inhibited blue light mediated photomorphogenesis in wheat,which is opposite to the function of TaGBF1.In comparison with the parent wheat JN177,the introgression line SR3 had longer coleoptile,and smaller induction extent of TaGBF1 and inhibition extent of TaCKB4 under blue light,suggesting the possible association between TaGBF1-TaCKB4 and photomorphogenesis alteration of SR3.In order to clarify the regulatory relationship between TaGBF1 and TaCKB4,we explored the expression pattern of TaCKB4 in wheat TaGBF1 overexpression and RNAi lines under different light.The results showed that under white and blue light,the expression of TaCKB4 was inhibited in TaGBFl overexpression lines,but was improved in the RNAi lines,which was not found in the dark.ChIP-qPCR indicated that TaGBF1 can bind to the promoter of TaCKB4.In line with the previous results,we primarily speculated that TaGBF1 may promote blue light mediated photomorphogenesis via inhibiting TaCKB4.BiFC assay showed that TaCKB4 interacted with TaHY5 in the nucleus.In Arabidopsis,the expression of the target genes of HY5 was inhibited by TaCKB4 ectopic expression but improved by TaGBF1 ectopic expression under white and blue light;no effect was found under dark.Consistently,in wheat,TaGBFl overexpression promoted the expression of HY5 target gens,but RNAi had the opposite effect.These data showed that TaGBFl-TaCKB4 may be involved in blue light mediated photomorphogenesis via HY5.Under salt stress,TaCKB4 overexpression reduced the germination rate of wheat,showing TaCKB4 played negative role in salt tolerance.TaCKB4 overexpression increased the sensitivity of germination to ABA,and promoted the expression of WABI5 under ABA and salt treatments.The interaction between TaCKB4 and WAB15 was confirmed by the BiFC and Y2H methods.These data primarily indicated that TaCKB4 may reduced salt tolerance at germination stage via ABI5.Since TaCKB4 is involved in the response to salt stress and blue light-mediated photomorphogenesis,we initially analyzed the regulation of TaCKB4 on ABI5 and HY5 under white light and blue light,and found that there are certain differences.This indicated that light quality may affect the role of TaCKB4 in salt stress.In summary,we analyzed the mechanism of TaCKB4 in blue light-mediated photomorphogenesis and salt stress response,and initially clarified the function of TaCKB4 in wheat light signal and ABA signal pathway.