The Mechanism Mediated By MYB4 In Response To Salt Stress

Soil salinization is the key factor to restrict plant growth and crop yield.Therefore,it is of great theoretical significance and practical value to find and explore salt-tolerant genes for crop stress-tolerance genetic improvement.MYB transcription family is one of the largest and most versatile transcription factors in plants,which is widely involved in the regulation of plant growth and development and environmental stress response.It has been reported that MYB4 gene is involved in the regulation of plant drought,cold,and UV-B stresses.However,its role in response to salt stress is unclear.In this study,MYB4 gene was proved to be involved in the regulation of plant response to salt stress.The main results are as follows:1. RT-qPCR analysis showed that the transcription level of MYB4 gene reachedthe highest in response to 100 m M NaCl for 1 h,and then decreased gradually,indicating that expression of MYB4 gene was induced by salt stress.2. Under 100 m M and 150 m M NaCl stress,the mutant myb4-1 is sensitive to saltstress,while the MYB4-overexpressing plants are tolerant to salt stress compared with the wild type,indicating that the transcription factor MYB4 is important in regulation of salt stress in plant.3. There was no significant difference in the growth phenotype between the wildtype and the myb4-1 mutant under mannitol,ABA,potassium chloride,and lithium chloride stresses,suggesting that MYB4-mediated salt sensitivity may be caused by the specific Na~+.4. Analysis of sodium and potassium content showed that the Na~+content in theroots of myb4-1 mutant was significantly higher than that in the wild-type,but the Na~+content in the leaves of myb4-1 mutant was not significantly different from that of the wild-type;There was no significant difference between Na~+content in the roots of the overexpressing plants and that in the wild-type,but Na~+content in the leaves of the overexpressing plants was higher than that in the wild-type.It can be speculated that the transcription factor MYB4 may be involved in regulating Na~+accumulation and compartmentation.5. The expression of genes related to NaCl stress response was further analyzed by q RT-PCR.The results showed that the transcription levels of SOS1,SOS2,SOS3,HKT1and NHX4 genes in myb4-1 mutant after NaCl stress were significantly lower than those of the wild type.The expression of the above genes significantly increased in MYB4-overexpressing plants.This indicates that the MYB4 gene may promote the efflux of some Na~+by activating the SOS signal pathway,and part of the Na~+enter into the xylem,Na~+stored in the xylem parenchyma cells by transport protein HKT1,and the transport protein NHX4 which located on the vacuole membrane absorb Na~+into the vacuole,thereby increasing the plant tolerance to high salt toxicity.6. Relationship between MYB4 and SOS1,SOS2,SOS3,HKT1 and NHX4 wasfurther studied by using tobacco transient expression experiments.It was found that MYB4 can activate the expression of SOS1,SOS3,HKT1 and NHX4.7. Through chromatin immunoprecipitation(ChIP)experiments,it was found thatMYB4 has three binding sites in the SOS1 promoter region,one binding site in the SOS3promoter region,one binding site in the HKT1 promoter region,and one binding site in the NHX4 promoter region.It can be seen from the results that MYB4 may directly activate the expression of salt-tolerant genes by binding the promoters of SOS1,SOS3,HKT1 and NHX4,thereby improving the salt tolerance of plants.The above results indicate that the transcription factor MYB4 is involved in the regulation of salt stress response by affecting the distribution of Na~+via the SOS signal pathway and the storage mechanism of HKT1 and NHX4.