The Function Of MYC1a/1b Transcription Factors In Nicotine Synthesis

Nicotine is an important alkaloid in tobacco,and its content is related to many factors.Genetic factors,cultivation conditions,plant hormone,biological stress and abiotic stress such as topping,bifurcation,insect bites,drought and low temperature will affect the synthesis of nicotine.Topping can cause the nicotine content in tobacco plant rapidly increase.On the analysis of nicotine synthesis induced by topping,we found that MYC1 a and MYC1 bwere two topping responsive transcription factors.Of MYC transcription factors in plants,MYC2 is studied the most clearly.MYC2 protein is a regulating factor in jasmonic acid hormone signaling pathways.It had been documented that MYC2a/2b were involved in regulation of nicotine synthesis through combining with G-box structure in PMT gene promoter.Since MYC2a/2band MYC1a/1b belong to MYCtranscription factors family,it is not clear that MYC1a/1b were also involved in nicotine synthesis regulation.Our previous works showed that the expression of PMT significantly increasedin transgenic tobacco plant with overexpression of MYC1a/1b,indicatingthat MYC1a/1b was involved in nicotine synthesis.In this paper,the functionsof MYC1a/1bwere studied,and the main results are followings.1.The transgenic tobacco plants were identified,and nicotine content and the expression of PMT were detected.The PMT expression and nicotine content significantly increased in transgenic plant with over-expression of MYC1a/1b,and they obviouslydecreased in transgenic tobacco plants with silence of MYC1a/1b.These results showed that MYC1a/1b was involved in the regulation of nicotine synthesis.2.Through GUS report gene expression analysis,Yeast one-hybrid and electrophoretic mobility shift assay,it was proved that MYC1a/1b transcription factor can bind G-box in the promoter of PMT.Therefore,MYC1a/1b transcription factor were involved in the regulation of nicotine synthesis by regulating the expression of PMT.3.There were obviously different in the promoters of MYC2a/2b and MYC1a/1b,indicating that their expressions were regulated by different regulatory factors.The expression analysis of MYC2a/2b and MYC1 a /1b showed that they had different responses to diverse stress.Although MYC1a/1b and MYC2a/2b had the same function of regulating nicotine synthesis,but their regulatory factors were different.