Molecular regulation of apple and grape ripening: exploring common and distinct transcriptional aspects of representative climacteric and non-climacteric fruits

Fleshy fruits of angiosperms are organs specialized for promoting seed dispersal by attracting herbivores and enticing them to consume the organ and the contained seeds. Ripening can be broadly defined as the processes serving as a plant strategy to make the fleshy fruit appealing to animals and leads to a coordinated series of changes in color, texture, aroma and flavor, as result of an intricate interplay of genetically and epigenetically programmed events. The ripening of fruits can be categorized into two types: climacteric, which is characterized by a rapid increase in respiration rate typically accompanied by a burst of ethylene production, and non-climacteric, where this pronounced peak in respiration is absent. Here we review the most current knowledge on transcriptomic changes taking place in apple (climacteric) and grapevine (non-climacteric) fruit during ripening, with the aim to highlight specific and common hormonal and molecular events governing the process in both species. In this perspective, we found that specific NAC transcription factor members participate in the ripening initiation in grape and are involved in the attempt to restore the normal physiological ripening progression in impaired fruit ripening physiology in apple. These elements suggest the existence of a common regulatory mechanism operated by NAC transcription factors and auxin in the two species.