Mechanism Of ORANGE(OR) Gene Regulating Arabidopsis Thaliana In Response To Drought Stress

The ORANGE(OR)gene was discovered in the naturally mutated cauliflower orange head.It is widely found in plants but highly conserved among different plant species.Studies have shown that the OR gene is involved in regulating plant carotenoid biosynthesis and response to stresses.However,the function of the Arabidopsis thaliana OR gene in response to abiotic stresses is unclear.In order to investigate the response and mechanism of the AtOR in response to abiotic stresses in Arabidopsis,we investigated the induction of the AtOR under stress conditions such as drought,ABA,salt,and mannitol stresses.The results showed that the transcription level of AtOR gene was significantly up-regulated under ABA,drought and mannitol stresses.In this dissertation,wild-type(WT),ator mutants,overexpression AtOR lines(OE-1 and OE-2)were used as materials to test the germination and survival rates of different genotype Arabidopsis seeds under drought stress,and water loss rate of leaves,stomatal movement,and expression levels of ABA-and drought-stress genes.Studies shown that OE-1 and OE-2 were more tolerant to drought stress than WT and mutants,and AtOR enhances drought resistance of Arabidopsis by regulating ABA-mediated stomatal movement.The findings are as follows:(1)AtOR gene(AT5G61670)is located on chromosome 5 of Arabidopsis thaliana and the gene is 1573 bp in length.Bioinformatics analysis showed that the AtOR protein is composed of 307 amino acids,the molecular formula is C₁₄₉₃H₂₃₆₉N₄₁₁O₄₄₄S₁₉,and a total molecular weight of 33.78986k Da,which is presumed to be an unstable protein.Secondary structure prediction AtOR protein mainly consists of alpha helix and random coil.(2)Arabidopsis subcellular location prediction website SUBA4 predicts that AtOR protein exists in mitochondria,nucleus,plasma membrane,cytoplasm,plastid and other organelles,which is mainly located on the plastid and is related to the chaperone protein dna J.The results of tobacco transient expression experiments indicated that AtOR protein is localized in the chloroplast.Tissue-specific results showed that the AtOR gene is expressed in roots,stems,leaves,flowers and pods,but the highest expression level was in leaves.(3)The carotenoid content in the overexpressed lines was higher than that of wild-type and mutants by HPLC(High Performance Liquid Chromatography),indicating that the AtOR gene increased carotenoid content in Arabidopsis.The expression level of AtOR gene was significantly increased under ABA,drought and mannitol treatment,indicating that AtOR gene was induced by many abiotic stresses.(4)Drought treatment by stopping watering and irrigation of mannitol in the soil to simulate drought showed that AtOR gene enhanced the drought resistance of Arabidopsis.The leaf water loss rate of WT and ator mutants was significantly higher than that of OE-1 and OE-2,indicating that AtOR gene affected leaf water loss rate,increase leaf water content,and enhanced drought resistance of Arabidopsis thaliana.ABA-induced stomatal closure and inhibition of stomatal opening experiments showed that AtOR gene can respond to drought stress by regulating stomatal closure.(5)AtOR gene promotes ABA-and drought-related genes.The expression levels of ABA-and drought-related genes RAB18,RD29B,RD26,ADH1,ABI2,ABF2in AtOR overexpressed lines were significantly higher than that in WT plants.