Genome-Wide Analysis Of The Apple MYB Transcription Factor Allows The Identification Of MdMYB121and MdSIMYB1Gene Confering Abiotic Stress Tolerance

The MYB proteins comprise one of the largest families of transcription factors in plants.MYB transcription factors plays an important roles in meristem development, secondarymetabolism, cell cycle control, stomatal closure, biotic, and abiotic stresses of eukaryote. Agenome-wide analysis of this family has been carried out with the draft of complete genomesequence of several plant species. Members of MYB transcription factors has been identifiedby responding to abiotic stresses in some model species, such as Arabidopsis, rice, andsoybean, but limited in apple (Malus×domestica Borkh.). The growth and development offruit trees are influenced by the increased environmental pollution, drought, low temperature,and salt stress. The draft sequence of the apple genome can play a helpful role in identifyingMYB family of apple, unravel stress-related MYB genes, variety breeding and improvement.This study identified and characterized229apple MYB genes through genome-wide analysisand have been divided into subgroups. Then, two stress-responsible genes MdMYB121andMdSIMYB1were analysed for their roles in abiotic stresses.1.131Arabidopsis MYB gene sequences were used as queries in multiple databasesearches against the proteome and genome files that were downloaded GDR database(Genome Database for Rosaceae: http://www.rosaceae.org/) and through an HMM (HiddenMarkov Model) analysis using Pfam to identified229apple MYB gene models.2. A computational analysis was conducted using the apple genomic database to yield acomplete overview of the apple MYB family, including the phylogenetic analysis withArabidopsis MYBs, intron-exon organizations, the sequence features of the MYB DNA-binding domains, the carboxy-terminal motifs, and the chromosomal locations.3. Subsequently, the expression of20MYB genes, including14were chosen from stress-related subgroups, while another6ones from other subgroups, in response to drought, salt,cold, ABA at2h was examined. The results showed that these genes responds differently tothese abiotic stresses.4. The expression of MdMYB121and MdSIMYB1was remarkably induced by these fourtreatments, which indicating that they may involve in multiple biological processes.5. The MdMYB121and MdSIMYB1was then further functionally characterized. A transgenic analysis indicated that the overexpression of the MdMYB121and MdSIMYB1generemarkably enhanced the tolerance to high salinity, drought, and cold stresses in transgenictomato and tobacco plants, respectively.6. In this study, MdMYB121transgenic tomato plants accumulated less Na+andmaintained a lower Na+/K+ratio under high salinity, maintained higher water content underdehydration than the WT control plants, respectively. In addition, transgenic MdMYB121tomato plants reduced the membrane damage and promoted the accumulation of protectivecompounds against environmental stress.7. In conclusion, besides direct or indirect regulation of stress-responsive geneexpression, MdSIMYB1is also involved in stress tolerance by promoting and maintaining rootgrowth under stress conditions by regulating auxin-responsive genes and perhaps byinteracting with GL3-like proteins.8. Transgenic apple lines that were overexpressing MdMYB121and MdSIMYB1exhibited a higher tolerance to abiotic stress than the WT control, respectively.