The Metabolism Of Cell Wall Materials And Gene Expression During Fruit Ripening And Softening In Ziziphus Jujuba Mill.

Ziziphus jujuba Mill.is a traditional fruit tree in China with a simple classification as the fresh and the dry jujubes according to the property and application.The ripening and softening of the two types of jujube are different,and it is of great significance to study the texture change,cell wall metabolism and gene expression characteristics during the ripening and softening process.In this research,firstly,the typical fresh jujube ‘Dongzao' and dry jujube ‘Muzao' and ‘Junzao' during seven developmental stages and storage under room temperature in 30 days were used as materials.The firmness,the water content,the content of cell wall materials(including pectin and cellulose)and the activity of related enzymes(including PG,PE and Cx-cellulase)were measured.Then,a total of 15 genes involved in enzymes above and ripening and softening regulation in jujube fruit were chosen according to the annotation from transcriptome sequencing of ‘Dongzao' and ‘Junzao' fruits,and the relative expression levels at seven developmental stages were obtained by real-time quantitative PCR(RT-qPCR).The following findings were obtained.(1)There were no significant changes in firmness and water content during maturation in ‘Dongzao',while PG and PE were highly correlated with the degradation of pectin and fruit ripening,and PG and Cx-cellulase made significant effects on the unnatural softening in postharvest ‘Dongzao' fruit.A total-mature stage with a natural softening in ‘Muzao' and ‘Junzao' fruit was after the crispy maturation.Compared with ‘Dongzao' fruit,the characteristics of pectin(including the protopectin and soluble pectin)and the cellulose degradation in “Muzao' was different,which occurred during ripening stages,while that was during crispy maturation in ‘Dongzao'.The PG and PE in ‘Muzao' and ‘Dongzao'made significant effects on their own critical ripe stages,and the PE stared up the softening of ‘Muzao'.The effect of Cx-cellulase on the ripening in‘Muzao' was more significant than that in‘Dongzao',but the effect on postharvest softening in‘Dongzao' was more significant than that in‘Muzao'.(2)Based on the results of genome sequencing of ‘Dongzao' and ‘Junzao' fruit,a total of 107 genes were found in the process of maturation and softening of the jujube fruit,including pectin degrading enzymes,cellulases and hemicellulases in totally 11 gene families.The expression levels of one PG,six PEs,seven cellulose-regulating genes and eight hemicellulose-regulating genes were consistent with the changes of enzyme activity.The results indicated that there were great correlations between cell wall metabolic materials,related enzymes and regulating gene expression levels in ‘Junzao' fruit.The PE genes made a leading effect on softening,and kinds of cellulase gene families regulated the ripening and softening by combination,but PG genes were not the key factors of softening.In addition,?-Glu40 and Gal17-1 played key roles on the softening during late ripening in ‘Junzao' fruit.This research strengthened the understanding of the cell wall metabolism during ripening and softening in jujube fruit,explained the different mechanism of cell wall materials and related enzymes as well as regulating genes between fresh and dry jujubes,and helped with a deeper study on ripening regulation of fruit at gene level,and gave evidence of the importance for further study on the postharvest preservation and dry process of jujube fruit.