Functional Analysis Of Apple BHLH137-like Gene In Drought And Salt Stress

Apple（Malus domestica Borkh.）is one of the major fruit trees in the world,and China is the largest apple-producing country.Drought and soil salinization are important factors restricting the development of apple industry in the Loess Plateau.b HLHs are ubiquitous in plants and play an important role in plant stress response.In this study,apple MdbHLH137-like gene was cloned and the expression pattern changes of MdbHLH137-like gene under various stresses were analyzed.Using MdbHLH137-like overexpressed transgenic tomato plants and MdbHLH137-like RNA interference transgenic callus as research materials,through physiological and RNA-Seq analysis,the function of MdbHLH137-like in the process of drought and salt stress was preliminarily revealed.The main results are as follows:1.The full length of the apple MdbHLH137-like gene was 1077 bp,encoding a protein with a length of 358 aa,with a typical b HLH domain.The MdbHLH137-like promoter contains multiple cis-acting elements related to phytohormone and stress response.MdbHLH137-like protein was located in the nucleus,had self-activation activity,and interacted with MdbHLH30 protein,suggesting that it may function in the form of dimer.MdbHLH137-like gene expression was induced by drought,salt,PEG and cold treatments,suggesting that MdbHLH137-like might respond to various stressors.2.Overexpression of MdbHLH137-like enhanced the resistance of transgenic tomato under drought stress and salt stress.Under drought and salt stress conditions,the overexpressing MdbHLH137-like plants had lower electrolyte leakage and MDA,H₂O₂ and O₂^-content,as well as higher POD,SOD activity and chlorophyll content compared with wild type.Chlorophyll fluorescence observation showed that the degree of damage to the photosynthetic system of the overexpressed plants was lower.3.Interference with MdbHLH137-like reduced the tolerance of transgenic callus to osmotic stress and salt stress,and increased the sensitivity to ABA.It is speculated that MdbHLH137-like may regulate plant resistance through ABA-dependent pathway.RNA-Seq results showed that wild-type and interfering MdbHLH137-like callus differentially expressed genes were enriched in glycolysis/gluconeogenesis and glutathione metabolism.Osmotic stress enriched the differentially expressed genes in plant hormone signal transduction and MAPK signal pathway.salt stress enriched differentially expressed genes in plant hormone signal transduction and glycolysis/gluconeogenesis,as well as starch and sucrose metabolism pathway.