Bioinformatics Analysis Of Pear β-amylase Family And Identification Of PbBAM3 Gene Cold Resistance

Pear(Pyrus)is the third largest fruit compared with apples and citrus in China.It has a wide range of cultivation.However,it is because of the wide cultivation that pears are subject to more abiotic stresses,especially low temperature stress.Cold stress is one of major environmental limiting factors for pear yield and quality.Therefore,it is very important to identify genes related to abiotic stress tolerance in pears.β-amylase(BAM)is an important enzyme involved in conversion of starch to maltose in multiple biological processes in plants.Maltose,the only product of starch degradation,plays an important role in plant protection.Analysis of the expression of BAM gene family in different species showed that the expression of BAM gene family is transcriptionally induced by abiotic stress such as cold,salt or drought.However,there are few studies on BAM gene in pear.In this study,we analyzed the bioinformatics of BAM family genes and studied the BAM family gene PbBAM3 in pears.We determined subcellar localization and analyze its functions using PbBAM3-overexpressing lines and their WT plants in tobacco and pear,respectively.The main experimental results are shown as follows:1.In this study,we identified 17 PbBAM in the pear genome.Of these,12 PbBAM members were mapped onto 9 chromosomes and 5 other PbBAM genes were located on scaffold contigs.Based on gene structure,protein motif analysis,and the topology of the phylogenetic tree of the PbBAM family,we classified member genes into 4 subgroups.All PbBAM genes were found to contain typical glycosyl hydrolysis 14 domain motifs.Next,we used transcriptomic data to study gene expression during the response of drought and low temperate stress responses,and found that genes in Group B were related to drought and cold stress.We identified four PbBAM genes associated with abiotic stress in Pear.Finally,by analyzing expression of qRT-PCR under drought and cold stress,we found that PbBAM1a,PbBAM1b,PbBAM1c and PbBAM3 were associated with the pear abiotic stress response.2.The results show that the transcript level of PbBAM3 was greatly induced under cold,dehydration and salt,but repressed by maltose.Localization analyses showed that PbBAM3 was located in the chloroplast.Overexpression in tobacco or pear of PbBAM3 conferred enhanced tolerance to chilling stresses.Under cold stress,higher BAM activity and more accumulation of maltose and soluble sugars were found in the transgenic lines compared with the wild-type.Moreover,compared with WT,the transgenic lines could maintain the ROS homeostasis in vivo by regulating the activities of antioxidant enzymes.Taken together,these results suggested that PbBAM3 plays an essential role in cold tolerance by fine-tuning the starch breakdown and thereby increases the levels of maltose and soluble sugars,which might contribute to the cold tolerance as compatible solutes or antioxidants.