Functional Characterization Of Apple MYB Family Gene MdMYB48 In Response To Drought Stress

Apple(Malus domestica Borkh.)is one of the four major fruits in the world,and China is the largest apple-producing and consuming country.As an important horticulture crop,the growth and development of apples are often affected by a variety of abiotic stresses,including drought,salinity,and low temperature.The Northwest Loess Plateau is the largest apple producing area in our country,and drought and water-deficit is one of the main environmental constraints restricting the development of the apple industry in this area.MYB transcription factors play a key role in the abiotic stress response and resistance regulation of plants.The excavation of key genes for drought response in the MYB family and the detailed identification of their drought-resistance regulatory functions are of great significance to the stress-resistant molecular breeding of apples.In this study,we cloned a drought-response gene MdMYB48 from the MYB family of apples,and analyzed its expression pattern under different adversities.Through phenotypic comparison under transgene and drought treatment,the drought-resistance regulatory function of MdMYB48 in Arabidopsis and apples was identified in detail.The main results are as follows:1.The full length of the apple MdMYB48 gene was 720 bp in length,encoding a protein with a length of 239 aa.MdMYB48 promoter sequence contains multiple cis-acting elements which was related to stress response.MdMYB48 protein was localized in the nucleus.The expression of MdMYB48 was induced by drought,salt,ABA and low temperature stress.MdMYB48 protein had significant self-activation activity,which was in line with its transcription factor characteristics.2.We obtained MdMYB48-overexpressing Transgenic Arabidopsis plants through genetic transformation.Phenotypic identification showed that overexpression of MdMYB48 increased the resistance of transgenic Arabidopsis to drought stress.Under the treatment of 200 m M and300 m M mannitol,the seed germination rate,seedling root length and fresh weight of MdMYB48-overexpressing Arabidopsis were significantly higher than those of the wild type.Under drought stress,overexpression of MdMYB48 increased the proline content in the transgenic Arabidopsis leaves,and decreased the relative conductivity and MDA content,and the transcription levels of multiple stress-related genes were significantly higher than that of the wild type.On the other hand,overexpression of MdMYB48 reduced the sensitivity of transgenic Arabidopsis to ABA.Under 1 μM ABA treatment,the seed germination rate and seedling root length of MdMYB48-overexpressing Arabidopsis were significantly higher than those of the wild-type,and the transcription level of multiple ABA-related genes in transgenic Arabidopsis was significantly higher than that of the control.It is speculated that MdMYB48 may reduce the biosynthesis of ABA and play a negative regulatory role in the ABA pathway.3.Overexpression of MdMYB48 enhanced the tolerance of apple ‘Wanglin’ calli to osmotic stress.Under the treatment of 150 m M mannitol,the fresh weight of MdMYB48 transgenic apple calli was significantly higher than that of the control,and showed higher proline content.Expression analysis showed that the transcription level of stress-responsive genes in MdMYB48 transgenic calli was significantly higher than that of the control,indicating that MdMYB48 may increase the tolerance of transgenic calli to osmotic stress by promoting the transcription of stress-related genes.4.The transgenic apple plants with MdMYB48 overexpressed in roots were obtained by Agrobacterium rhizogenes infection with ‘GL3’ tissue cultured seedlings.Compared with the wild type,the overexpression lines had a higher plant height and more lateral roots.Under drought stress conditions,MdMYB48-overexpressing transgenic apple lines were more sensitive to drought stress than the control.The overexpression transgenic plants had less proline content and more MDA accumulation.Expression analysis showed that the transcription levels of drought and ABA response-related genes in MdMYB48 transgenic apple plants was lower than that of the control,indicating that MdMYB48 was involved in the drought stress response of apple plants.