Functional Studies On The Poplar MYB99 Transcription Factor In Drought Resistance

Drought is one of the most serious problem in the world,leading to crop yield reduction and environmental degradation,and it has received long-term and widespread attention.Generally,increasing the resistance of plants to drought is beneficial,but being able to grow quickly is also an important ability for plants,especially for cash crops,whose yield is a decisive factor.This requires plants to be able to grow normally and even quickly but also to have sufficient drought resistance.However,these two capabilities are often difficult to achieve at the same time,because these two capabilities often require the same features to develop in different directions.For example,the opening of stomates is beneficial to photosynthesis but makes plants more easily to lose water;on the contrary,after the stomates were closed,their drought resistance is improved but blocked photosynthesis.Therefore,in order to resolve such contradictions,it is necessary to make plants more ingenious and meticulous to respond to environmental changes such as water shortages.In order to achieve this goal,it is necessary to understand in detail how plants response to drought signals to adapt to environmental changes.At present,there had some understanding of how plants response to drought signals,and MYB transcription factors play an extremely important role in this process.MYB transcription factors were first founded in animals,but the number and diversity of MYB transcription factors in plants far exceed those in animals,and they are extremely widely involved in various physiological processes of plants.This indicates that MYB transcription factors play an important role in the fine regulation of various physiological processes in plants.Therefore,In this study,we selected the PtoMYB99 transcription factor which may be related to poplar response to drought,from Populus tomentosa MYB transcription factor family.And studied the function of PtoMYB99 in drought resistance.The main results are:(1)Bioinformatics,yeast one-hybrid,and subcellular localization experiments showed that PtoMYB99 transcription factor is a typical R2R3-MYB transcription factor,located at the nucleus and had the ability to activate downstream genes.(2)q RT-PCR and GUS staining experiments showed that the PtoMYB99 gene is highly expressed in the epidermis of the stem of Populus tomentosa,but the expression level is low in the leaves.(3)Response elements in promoter and induced expression experiments showed that PtoMYB99 gene can response to drought,salt stress and exogenous ABA treatments at the transcriptional level,and its expression is inhibited by drought and salt stress,but induced by exogenous ABA.(4)The overexpression of PtoMYB99 gene has no great influence on the growth of Populus tomentosa under suitable experimental environment.(5)The PtoMYB99 gene overexpression plants were treated with low concentration of salt,and its resistance was not significantly different from that of the wild-type plants,indicating that the PtoMYB99 gene was not involved in the response of sodium ion stress.(6)The PtoMYB99 gene overexpression plants were treated with 20% polyethylene glycol,and the phenotype showed that the overexpression plants were highly sensitive.And the detection of various physiological indexes showed that the transgenic plants were severely stressed.These results indicated the resistance of overexpression plants was significantly reduced compare with wild-type plants.Overexpression of PtoMYB99 gene significantly increased the transpiration rate,stomatal conductance,and photosynthetic rate of plants,and the stomata opening is significantly higher than that of wild-type plants,but the stomata density remains unchanged.(7)The hormone contents of PtoMYB99 gene overexpression plants and the q RT-PCR results of ABA and JA synthesis genes showed that PtoMYB99 can inhibit the synthesis of ABA and JA.Based on the above results,it can be concluded that the R2R3-MYB transcription factor PtoMYB99 of Populus tomentosa can inhibit the synthesis of ABA and JA by regulating the expression of ABA and JA synthesis genes,induce stomata opening,enhance transpiration rate,and reduce drought resistance.Moreover,ABA can induce the expression of PtoMYB99 gene,and the expression of PtoMYB99 gene inhibits the synthesis of ABA,forming a negative feedback regulation mechanism.