Correlation Of B-box Gene Family In Adaption To Chilling Of Peach Fruit During Postharvest Cold Storage And Subsequent Shelf Life

B-box transcription factors play an important role in plant growth and development,including seedling photomorphogenesis,shade avoidance,photoperiodic regulation of flowering,and responses to biotic and abiotic stresses.However,at present,information is lacking on the B-box genes in peach(Prunus persica L.Batsch).Many studies have been published on the B-box genes’ response to light,but far fewer on low temperature response.In this study,through bioinformatics approach,we identified 22 members of the B-box gene family in peach and provided an integrated overview of phylogenetic analysis,conserved domain analysis,cis-element prediction,and so on.In order to further explore the role of B-box gene family in fruit chilling adaptation,the ‘Jinxiu’ peach fruit were used as the materials and stored at 0 ℃ and 4 ℃ for 28 days(d).After stored for 7d,14 d,21 d and 28 d,they were transferred to 20 ℃(shelf life)for 3 d respectively.Then we checked the occurrence of chilling injury.By analyzing the response of each Bbox gene family member to low temperature and their correlation with chilling injury(CI)factor such as Internal browning(IB)and electric conductivity(EC),we aimed to mine out candidate BBX genes participating cold adaptation of peaches during low temperature storage,and finally analyzed its possible mechanism.The results not only lay a foundation for further functional characterization of the B-box gene family members,but also provide new insights into the response of low temperature and CI for postharvest peach fruit.The main results are as follows:1.During the post-harvest storage period,the firmness of peach fruit generally presented a downward trend,but there were significant differences between temperature treatments.At 4 ℃,the firmness dropped sharply from 52.28 N at harvest to 11.53 N after 14 d of storage and then further decreased to 3.46 N after 3 d of shelf life at 20 ℃.However,the peach fruit failed to soften normally after being transferred to the shelf life after 21 d and 28 d storage.At 0 ℃,the initial firmness(52.28 N)gradually declined to about 40 N during the whole cold storage period.Fruit showed a normal softening pattern during 3 d of shelf life after 7 d,14 d,21 d and 28 d of storage.For total soluble solids(TSS),their concentration in fruit generally showed an upward trend throughout the storage period.TSS concentration in peaches stored at 4 ℃ varied dramatically compared to that in peaches stored at 0 ℃;In contrast,the concentration of titratable acidity(TA)decreased during storage time,and TA concentration in peaches stored at 0 ℃ varied dramatically compared to that in peaches stored at 4 ℃;At 0 ℃,the ratio of TSS to TA fluctuates around 60.At 4 ℃,TSS/TA generally showed an upward trend,between 50-100.2.The successive increases in EC were showed in peach fruit during cold storage period plus 3 d of shelf life after transfer.Compared with peaches stored at 4 ℃,the EC value of fruit stored at 0 ℃ varied more steadily.After 21 d of storage at 4 ℃,peach fruit transferred to 20 ℃ for 3 d showed flesh internal browning(IB index = 29.17%).The internal browning of peach fruit increased significantly in severity after 28 d of storage at 4 ℃ and 3 d of shelf life(IB index = 62.50%),while fruit began to exhibit mild browning after 28 d of storage at 0 ℃ and 3 d shelf life(IB index = 8.33%).These results indicate that cold storage of 4 ℃ could induce the physiological disorder chilling injury in peach and 0 ℃ effectively delayed its occurrence.3.Using the peach genome data,22 peach B-box gene family members were identified.According to the number and type of conserved domains,B-box members were divided into 5 subfamilies.Exon-intron structure analysis showed that the motif 1was highly conserved in all BBX proteins,and the members of each subfamily had similar length and number of exons/introns and similar conserved motifs.Each member had a unique conserved motif.Chromosomal location results indicated that B-box genes were unevenly distributed on 6 chromosomes.Gene duplication events showed that some segmental duplications(Pp BBX14,15 / Pp BBX19-1,19-2 / Pp BBX20,21 / Pp BBX26,28/ Pp BBX26,29 / Pp BBX28,29)were detected on the peach chromosomes.Synteny analysis demonstrated that Pp BBX6,Pp BBX11 and Pp BBX12 were highly conserved among the six representative plant species.Analysis of cis-acting elements revealed that22 BBX genes contained 43 cis-acting elements in total,among which Pp BBX3,6,10,12,15,19-2,20,22,and 26 contained LTR(Low temperature response)cis-elements(CCGAAA),indicating that these genes may respond to low temperature.4.Using qRT-PCR to analyze the expression patterns of B-box genes in peach fruit under different treatment conditions,it was found that the expression level of them in the fruit under storage of 0 ℃ was higher than that under storage of 4 ℃,indicating that 0 ℃ has the ability to induce BBX genes expression,while 4 ℃ delayed the expression of them.During low-temperature storage,Pp BBX3,5,6,12,15,20,24-2,26 and 29 have similar expression patterns: When peaches were stored at 0 ℃,gene expression level showed a gradually upward trend from 1 d to 21 d.Compared with peaches stored for 7d and 14 d,the gene expression level reduced after storage for 7 d and shelf life of 3 d and 14 d and shelf life of 3 d.Gene expression peaked on the 21 d and then began to decline.Similarly,compared with peaches stored for 21 d and 28 d,the gene expression level reduced after storage for 21 d and shelf life of 3 d and 28 d and shelf life of 3 d.5.The correlation analysis between gene expression and IB and EC showed that the expression patterns of B-box genes were correlated with the occurrence of CI.Pp BBX6,24-1,5,32,26,15,14,24-2,11,3,20,29,12 and IB were significantly negatively correlated(p <0.05),and Pp BBX6,15,24-2,27,5,24-1,29,20,3,30,26,12 expression levels and EC showed a significant negative correlation(p <0.05).Therefore,judging from the correlation between cold injury factors and gene expression,the expression levels of Pp BBX3,5,6,12,14,15,20,26,29,24-1,24-2 had a significant negative correlation with the occurrence of CI.In summary,we identified 22 B-box gene family members in total by bioinformatics.Based on gene expression pattern,correlation,and cis-acting elements analysis,it is speculated that Pp BBX3,6,12,15,20,26 in the peach B-box gene family play a potential positive role in chilling adaptation and delay the occurrence of CI symptoms of peaches during cold storage and subsequent shelf life,but its molecular mechanism still needs to be further studied.