| Jasmonic acid（JA,jasmonate）is a key hormone that mediates plant response to environmental signals and endogenous signaling substances.It participates in the normal growth and development of plants,including embryo differentiation,stomatal movement,pigment synthesis,seed germination,root growth,pollen development,fruit ripening and senescence and a series of physiological activities.In addition,jasmonic acid induced plants to make a defensive reaction in defensing pest,disease and other biological stress and high temperature,high salt,hypertonic and other non-biological stress.JA plays an important role in plant stress resistance.It is important practical significance in increasing crop yield and improving crop quality.Therefore,there will be important scientific value in studying molecular regulate mechanism of jasmonic acid in crops.In the JA-signaling pathway,the F-box protein CORONATINE INSENSITIVE 1（COI1）forms SCFCOI1 ubiquitin ligase with other receptor proteins,which mediates the JA-signaling pathway.The association of SCFCOI1 complex with JA-Ile,the active derivative of JA,selectively recruit regulatory proteins,such as JAZs,targeted for ubiquitination then degraded by 26 s proteasome in a JA dependent way.Thus it releases the transcription activators MYC2 and MYB,which activates the expression of downstream growth and development and stress response gene in JA-signaling pathway,and regulates plant physiological response.The COI1 protein is a critical component of the JA receptor,and the lack of COI1 gene will cause the plant to lose all the jasmonate response.Recent studies have shown that the JA-signaling pathway and COI1 protein play an important role in the regulation of plant primary metabolism and leaf senescence.And they also can regulate starch accumulation in plant photosynthesis and the expression of senescence-related gene in the process of leaf senescence.However,the molecular and physiological regulatory mechanisms associated with this regulatory process have not been studied in depth.In order to reveal the physiological regulation mechanism of JA-signaling pathway in regulating the process of plant leaf senescence and carbohydrate metabolism.In this study,we have carried on the thorough research to this physiological process from the regulation function of jasmonate receptor protein COI1.We generated NtCOI1-silenced transgenic tobacco（Nicotiana tabacum L.cv.TN90）,and allows examination of the effects of NtCOI1 silencing on various aspects of plant primary metabolism under the conditions of exogenous jasmonate.There was a significant change in the level of starch metabolism and the expression of starch metabolism related genes.Our study provides compelling molecular evidence that NtCOI1 functions to control primary carbohydrate metabolism.Therefore,we demonstrated the effects of exogenous jasmonate on plant glucose metabolism related genes and senescence-related genes to study the role of COI1 in JA-induced primary metabolism and leaf senescence.In this study,we used TN90 and NtCOI1-silenced transgenic tobacco as materials,for finding the physiological and molecular mechanisms of the effects of exogenous MeJA and different light treatment conditions on tobacco.The main results were as follows:1.Previous studies revealed that Arabidopsis thaliana seedlings did not turn yellow with 100μM MeJA treatment for 1 week.However,we find that 6 leaves stage of TN90 were treated with 100μM MeJA turned yellow.It was indicated that there are differences in jasmonate response reaction between tobacco and Arabidopsis thaliana.2.The 6 leaves stage of TN90 were treated with H2O and 100μM MeJA in bright light and dim light,respectively.In bright light,the leaves treated with MeJA were significantly yellow after 1 week,while the leaves in control stay green.In dim light,all leaves treated did not turn yellow.It is more significant after 2 weeks.The results showed that there was no more obvious change after 3 weeks,and the situation was basically stable.The same treatment was conducted on COI1 seedlings at 6 leaves stage,while all the tobacco seedlings treated were not yellowing.It was indicated that jasmonate can induce tobacco leaves chlorosis under light conditions,and this regulation process depends on the biological function of jasmonate receptor protein COI1.3.All the treated seedlings in the results 2 were sampled at 1,2 and 3 weeks.And the total sugar content was measured.The results showed that the contents of glucose and starch were significantly decreased after MeJA treatment compared with control group in TN90 seedlings.However,the content of glucose and starch of MeJA treatment was higher than the control group in COI1 seedlings.In dim light,the contents of glucose and starch were not significantly changed after MeJA treatment in TN90 and COI1 seedlings.In the same MeJA treatment conditions,the contents of glucose and starch in COI1 seedlings were significantly higher than TN90 seedlings.It was indicated that the photosynthesis of tobacco seedlings could be inhibited during the process of tobacco leaves chlorosis induced by MeJA and the carbohydrate metabolism of tobacco leaves could be changed.4.Leaf chlorosis is one of the important characteristics of plant senescence,and many studies have shown that the process is closely related to the expression of plant senescence-related genes.The results of qRT-PCR showed that there was no significant difference in the expression level of senescence-related genes SAG12,SagL1,SagL2,SeR1,SeR2,Xyl1,Xyl2,Xyl4 and starch metabolism genes AGPs,SS2,BAM1,BAM2.The results showed that JA-induced leaf chlorosis and the changes of carbohydrate metabolism were not closely related to the expression of senescence-related genes.Previous studies on Arabidopsis thaliana have been shown to be closely related to the expression level of senescence-related gene in dark.In this study,we demonstrated that JA-induced tobacco leaf chlorosis was not closely related to senescence-related gene under normal light conditions.This study shows that JA-induced plant leaf chlorosis is a complex regulatory process. |
