TPS-b family genes involved in signature aroma terpenes emission in ripe kiwifruit

Aroma is a critical factor influencing consumer acceptability of ripe fruit. When fruit are eaten, the aroma travels retronasally from the mouth into the olfactory receptors located in the nose after exhaling. In kiwifruit (<i>Actinidia</i> spp.), terpene volatiles such as α-terpinolene and 1,8-cineole have been shown to contribute to the characteristic aroma of ripe fruit. Notably, 1,8-cineole contributes a key floral/eucalyptus note to the aroma of ripe <i>A. chinensis</i> ‘Hort16A’ kiwifruit, based on sensory descriptive and discriminant analysis. Emission of α-terpinolene and 1,8-cineole in kiwifruit is induced by ethylene, and production peaks when fruit are at eating ripeness. Two monoterpene synthase TPS-b family genes have been isolated from the fruit of <i>A. arguta</i> and <i>A. chinensis</i> that produce α-terpinolene and 1,8-cineole, respectively. Here we discuss terpene volatiles with respect to fruit aroma and consumer sensory evaluation, analyze the gene structure and conserved motifs of TPS-b genes in published kiwifruit genomes and then construct a transcriptional regulatory network based on <i>Actinidia</i> TPS-b. These data provide further insights into the potential molecular mechanisms underlying signature monoterpene synthesis to improve flavor in kiwifruit.