Regulation By Nitric Oxide On Uracil DNA Glycosylase In Peach Fruit

Peach fruit is a respiratory climacteric fruit,which is more sensitive to temperature.After harvesting,it breathes vigorously and is easy to soften and rot.Low temperature is often used for peach fruit storage,but low temperature can easily cause chilling damage to peach fruit.Mitochondria is the main part of aerobic respiration and plays an important role in various metabolic processes.Chilling injury can easily lead to mitochondrial damage and dysfunction.The protein encoded by mitochondrial DNA（mitochondrial DNA,mt DNA）is the key to the assembly and activity of many mitochondrial respiratory complexes,and is necessary to maintain mitochondrial function.Damaged mt DNA will lead to abnormal mitochondrial function.Nitric oxide（NO）is a signaling molecule in various plant metabolic pathways,and can participate in the regulation of mitochondrial function and fruit quality.However,the effect of NO on delaying mitochondrial and mt DNA oxidative damage is unclear.In this paper,postharvest peach fruits were treated with NO and c-PTIO（NO scavenger）respectively,and the effects of NO on mitochondrial function,antioxidant system in mitochondria,mitochondrial DNA damage,and mt DNA base excision repair（BER）pathway and the regulatory role of uracil DNA glycosylase（UDG）in the BER pathway.There were some results as below:（1）NO treatment increased the activity of antioxidant enzymes and ascorbate-glutathione（As A-GSH）pathway enzymes,and up-regulated the transcription levels of related genes,which enhanced the ability of mitochondria to scavenge reactive oxygen species（ROS）and relieved the accumulation of ROS in mitochondria.It helps to maintain the redox balance of mitochondria,reduce mitochondrial damage,and maintain the shape and function of peach fruit mitochondria during cold storage.（2）NO reduces the number of AP sites and increases the relative copy number of mt DNA by reducing the content of ROS and 8-hydroxydeoxyguanosine（8-OHd G）in mitochondria.In addition,NO up-regulated the activities of enzymes and gene expression levels related to BER pathway,which contributed to the improvement of mt DNA replication ability.（3）The Pp UDG gene in peach fruit was cloned by reverse transcription-polymerase chain reaction（RT-PCR）,and the full-length CDS region was 1119 bp,encoding a total of372 amino acids.According to the biological analysis of Pp UDG sequence,the molecular formula of the protein is predicted to be C₁₈₄₄H₂₉₃₂N₅₂₂O₅₃₅S₁₂,which is hydrophobic,and there is no transmembrane region and signal peptide region.The results of subcellular localization indicated that the target organelle of Pp UDG gene was mitochondria.Through overexpressing the Pp UDG gene in tomato and peach fruits,the results show that overexpression of Pp UDG can enhance the transcription level of BER pathway-related genes,reduce mt DNA damage in tomato and peach fruits,improve the self-replication ability of tomato and peach fruits mt DNA,and maintain mitochondrial function of tomato and peach fruit,and increase the antioxidant capacity of peach fruit by regulating the enzymatic antioxidant pathway,delay fruit rot,and reduce oxidative damage of peach fruit.Therefore,NO regulates the enzymatic and As A-GSH antioxidant systems,enhances mitochondrial antioxidant capacity,and reduces mitochondrial damage;NO activates the BER pathway,improves the repair efficiency of damaged mt DNA,and helps maintain the integrity of mt DNA.Overexpression of Pp UDG can effectively maintain the integrity of mt DNA,maintain mitochondrial function,and increase the antioxidant capacity of peach fruit.