Characterization Of MdMYB3 Under Drought Stress And Low Temperature Stress In Apple

Apple is one of the most important fruits in China.The Loess Plateau of China is considered as an advantageous areas where local people benefit from apple production.However,the environmental stress,such as drought and low temperature,frequently restrict the quality and yield of apple.In this study,a MYB transcription factor MdMYB3 was cloned from ?Golden Delicious?,and MdMYB3 overexpression plants were obtained by genetic transformation with GL-3 as background.The function of MdMYB3 in response to drought and cold was analyzed.The results were as follows:1.The MdMYB3 gene has 933 bp in its CDS and encode,310 amino acids.Protein sequence alignment revealed that MdMYB3 belongs to the R2R3 MYB transcription factor and has a typical MYB conserved domain.Subcellular localization showed that MdMYB3 was located in the nucleus.The patterns of MdMYB3 expression were also analyzed.It was found that MdMYB3 was expressed in roots,stems,and leaves,and the highest expression level was found in roots.Additionally,the MdMYB3 was obviously induced in leaves and roots of apple seedlings in response to drought and low temperature treatments,and the highest expression level appeared after 3 hours stress treatment.2.The wild type GL-3 and MdMYB3 overexpression plants were subjected to a short-term drought treatment.The wilting degree of GL-3 leaves was significantly longer than MdMYB3 overexpression plants after 10 days drought treatment.At the same time,the photosynthetic rate and antioxidant enzyme activity of MdMYB3 overexpression plants were higher than those of GL-3,suggesting that the MdMYB3 overexpression plants exhibited stronger drought resistance;however,ion leakage and hydrogen peroxide content of transgenic plants were lower than those of GL-3 plants,indicating that MdMYB3 had a positive role in improving the drought resistance of apple plants.3.Analysis of high-throughput transcriptome sequencing data showed that the differentially expressed genes between GL-3 and transgenic plants were mainly enriched in flavonoid biosynthesis and benzene compounds biosynthesis,sesquiterpene,triterpene biosynthesis,carotenoid biosynthesis,photosynthesis,and anthocyanin synthesis pathways.Furthermore,q RT-PCR was performed to verify the expression of some selected key genes including Md CHS,Md CHI,Md DFR,Md ANS,Md ANR,Md ERF1 B,MYBPA1,Md GST30,Md WRKY53,Md LAC5,etc.The result indicated that MdMYB3 positively regulated the expression of genes related to synthesis of anthocyanin,proanthocyanidin,redox and lignin.4.Under low temperature conditions(4°C),the content of anthocyanin and the activity of antioxidant enzymes(SOD,CAT,GST,POD)in the MdMYB3-overexpressing lines were significantly higher than those of GL-3,however,the hydrogen peroxide content was significantly lower than that of GL-3.Moreover,transgenic plants exhibited lower ion leakage at-6oC than that of GL-3 before and after cold acclimation.The above results suggested that MdMYB3 improved the cold resistance of apple plants under low temperature stress.5.Analysis of high-throughput transcriptome sequencing data showed that significantly differentially expressed genes were mainly enriched in phenylpropane biosynthesis,anthocyanin biosynthesis,and biosynthesis and metabolism,pigment biosynthesis,and glutathione metabolism,q RT-PCR was performed to verify the expression of selected genes including Md CHS,Md CHI,Md DFR,Md ANS,Md GST30,and Md LAC17.The results indicated that MdMYB3 positively regulates the expression of genes involved in anthocyanin synthesis,oxidation,and lignin synthesis under low temperature stress.