Beyond Ethylene: New Insights Regarding the Role of AOX in the Respiratory Climacteric

Abstract

Climacteric fruits are characterized by a dramatic increase in autocatalytic ethylene production, which is accompanied by a spike in respiration, at the onset of ripening. The change in the mode of ethylene production from autoinhibitory to auto-stimulatory is known as the system 1 (S1) to system 2 (S2) transition. Existing physiological models explain the basic and overarching genetic, hormonal, and transcriptional regulatory mechanisms governing the S1 to S2 transition of climacteric fruit. However, the links between ethylene and respiration, the two main factors that characterize the respiratory climacteric, have been largely understudied at the molecular level. Results of recent studies indicate that the AOX respiratory pathway may play an important role in mediating cross talk between ethylene response, carbon metabolism, ATP production, and ROS signaling during climacteric ripening. New genomic, metabolic, and epigenetic information sheds light on the interconnectedness of ripening-associated metabolic pathways, necessitating expanding the current, ethylene-centric physiological models. Understanding points at which ripening responses can be manipulated may reveal key, speciesand cultivar-specific targets for regulation of ripening enabling superior strategies for reducing postharvest wastage.

Glyoxylic acid overcomes 1-MCP-induced blockage of fruit ripening in Pyrus communis L. var. ‘D’Anjou’

“…Ripening in climacteric fruit has primarily been attributed to biosynthesis of ethylene. It is clear, however, that the nuances of ripening extend far beyond ethylene production and respiration [52]. Due to complex requirements for S1-S2 transition in European pear, the fruit may serve as a useful system in which to explore the vagaries of the ripening process in climacteric and non-climacteric fruit [52].…”

“…It is clear, however, that the nuances of ripening extend far beyond ethylene production and respiration [52]. Due to complex requirements for S1-S2 transition in European pear, the fruit may serve as a useful system in which to explore the vagaries of the ripening process in climacteric and non-climacteric fruit [52]. This study addresses a knowledge gap in the ripening process in pear, epitomized by the inability of 1-MCP treated fruit to regain ripening capacity naturally and paralleled with the discovery that GLA can overcome the 1-MCP blockage.…”

Heat stress, not water stress, dominates in eliciting metabolic and transcriptomic responses of grape berries

“…In most cases, HS and HWS had the greatest impact on reduction of transcriptional activity. Transcription associated with alternative respiration (AOX homolog, ubiquinol oxidase 2) was elevated in Riesling but repressed in Cabernet Sauvignon-the AOX gene is activated in response to stress and plays a role in reduction of ROS (Hewitt and Dhingra, 2019). The heightened expression in Riesling may be indicative of an elevated ROS scavenging response in this variety.…”

Evidence for the Involvement of Vernalization-related Genes in the Regulation of Cold-induced Ripening in ‘D’Anjou’ and ‘Bartlett’ Pear Fruit

“…A prominent aspect that distinguishes European pear and Chinese white pear (Pyrus bretschneideri Rehder.) from most other climacteric fruits is that these species have a pre-ripening period, during which they require a specific amount of cold exposure in order to transition from S1 to S2 ethylene production 6,7 . The process of cold exposure is called 'conditioning' , and accumulation of chilling hours necessary for this transition, and therefore ripening initiation, is referred to as the 'chilling requirement' 8 .…”