As major contributors to flavor in many fruit species, volatile esters are useful for investigating the regulation of the biosynthesis pathways of volatile aroma compounds in plants. Ethylene promotes the biosynthesis of volatile esters during fruit storage while accelerating fruit ripening; thus, the ethylene perception inhibitor 1-Methylcyclopropene (1-MCP) is employed to prolong the shelf life of fruits. However, the mechanisms by which 1-MCP regulates volatiles synthesis remain unclear. In this study, we analyzed the pathway of 1-MCP-mediated volatile ester synthesis in ‘Nanguo’ pear (Pyrus ussuriensis). 1-MCP significantly decreased volatile ester synthesis during storage. Comparative transcriptome analysis showed that the genes encoding two transcription factors (PuNAC37, PuWRKY74) and a RING-type E3 ubiquitin ligase which have a domain of unknown function (PuRDUF2) were expressed at high levels, whereas ALCOHOL ACYLTRANSFERASE 1 (PuAAT1), encoding an enzyme responsible for volatile ester synthesis, was expressed at low levels in 1-MCP-treated fruit. Moreover, PuNAC37 inhibited the expression of PuWRKY74 via transcriptional regulation, whereas PuNAC37 and PuWRKY74, after directly binding to the promoter of PuAAT1, synergistically inhibited its expression in 1-MCP-treated fruit. In addition, in vitro and in vivo ubiquitination experiments revealed that PuRDUF2 functions as an E3 ubiquitin ligase that ubiquitinates PuAAT1, causing its degradation via the 26S proteasome pathway following 1-MCP treatment. Subsequent PuAAT1 degradation resulted in a reduction of volatile esters during fruit storage. Our findings provide insights into the complex transcriptional regulation of volatile ester formation in ‘Nanguo’ pears and contribute to future research on AAT protein ubiquitination in other species.

The aroma of fruit is an important indicator that reflects the quality of its flavor. The ‘Nanguo’ pear (Pyrus ussuriensis Maxim.) is a typical fruit in Liaoning Province, China, that has an attractive aroma during fruit ripening. Fruit volatile compounds are primarily composed of esters, alcohols, aldehydes, ketones, lactones, terpenoids and apocarotenoids. The primary characteristic volatile compounds of the ‘Nanguo’ pear are esters. The contents of aldehydes decrease, and the contents of esters increase as the fruit ripens. The aroma changes from ‘green’ to ‘fruity.’ Thus, it has been a favorite of consumers in China and throughout the world for its attractive aroma. This review systematically summarizes advances in the research methods, components, types and biosynthetic pathways of volatile compounds, and the factors that affect the aroma volatiles in the ‘Nanguo’ pear, particularly the regulation by hormones that has been studied in recent years and delineates the research problems and prospects. The aim is to provide critical information for further research on the qualities of fruit flavor and provide a more scientific basis to improve the quality of fruit flavor during the development and storage of the ‘Nanguo’ pear.