Genome-wide identification of CXE and PuCXE15 functions in the catabolism of volatile ester in ‘Nanguo’ pear fruit

Volatile esters are the main aromatic components that affect consumer sensory preferences. Aroma is a crucial characteristic of the 'Nanguo' pear (Pyrus ussriensis Maxim). Carboxylesterases (CXEs) are positively correlated with the catabolism of volatile esters in peaches; however, the mechanism of action of CXE family members in 'Nanguo' pear is poorly understood. In this study, 40 PuCXEs were identified in the 'Nanguo' pear and assigned into seven groups. In addition, we found that most PuCXEs were relatively conserved and contained cytoplasmic proteins. This hypothesis was supported by phylogenetic analysis, investigation of conserved domains and gene structures, and prediction of subcellular localization. Based on the content of volatile esters and expression levels of PuCXEs analysis, four PuCXEs, including PuCXE7, PuCXE15, PuCXE20, and PuCXE25, had a significant negative correlation with volatile ester accumulation. Particularly, the correlation of PuCXE15 far exceeded that of the other PuCXEs. The results of the transient expression assay showed that PuCXE15 promoted the degradation of ester in vivo. Subcellular localization experiment revealed that PuCXE15 is located in the plasma membrane and nucleus. These results show that PuCXE15 functions in the catabolism of volatile ester in 'Nanguo' pear fruit, and provides a foundation for enhancing aroma quality by artificial control in pear.