Ripening and senescence of fleshy fruits

Authors: ANWAR, RAHEEL - University Of Faisalabad; Mattoo, Autar; HANDA, AVTAR - Purdue University

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 2/26/2018
Publication Date: 1/1/2019
Citation: Anwar, R., Mattoo, A.K., Handa, A.K. 2019. Postharvest Biology and Nanotechnology. New Jersey: Wiley Publishers. 403 p.

Interpretive Summary: Fruits grown in the tropics and subtropics amount to over 1.2 billion tons, much of it for fresh consumption. Fruits are considered as important sources of fiber, vitamins, minerals and antioxidants. Since ripe fruits are among significant primary components of the food supply chain, understanding their ripening physiology is important for developing strategies to extend shelf-life and maintain quality of fruit from farm to fork. Also, delineating important aspects of food quality, safety and security are important to human health and nutrition. With the increasing surge in per capita consumption of fresh fruits and vegetables, enhancing fruit nutritional quality and sensory attributes has gained much attention in recent years. This invited book chapter provides a review of recent progress made in understanding ripening and senescence of fleshy fruits, together with genetic regulation and processes involved in the accumulation of nutrients, volatiles and aroma compounds. This information will be useful to fruit growers, agricultural scientists and fruit technologists.

Technical Abstract: Fruit ripening involves complex transcriptional regulatory networks. Recent advancement in genetic and biotechnological techniques and enrichment in genetic resources has facilitated identification and characterization of fruit quality genes. Furthermore, a plethora of knowledge emerging from transcriptomics, metabolomics, proteomics and combined systems biology studies is paving our way to understand molecular mechanisms underlying fruit ripening. In addition to the elucidation of biosynthetic pathways, various transcription factors have been identified as major regulatory genes controlling fruit ripening and fruit quality attributes but crosstalk among them and their downstream factors is still in infancy and needs to be fully explored. It is clear that co-existence of negative and positive feedback mechanisms and synergism among them play important roles in controlling transcriptional and metabolic processes of fruit ripening in temporal and tissue-specific manner. High-resolution genome sequencing, advanced molecular techniques and improved statistical capabilities will further help to dissect these mechanisms within different cell types and cellular compartments. These high-throughput technologies have enabled us to reveal missing pieces in the puzzle of regulatory networks. There is need to explore connections between these regulatory networks and their downstream factors governing changes in fruit quality aspects. Though, much of the research to understand fruit ripening has been focused on tomato, there is a need for identifying various limiting and regulatory components of fruit ripening in other fruits with quite distinct anatomical structures and ripening features. Considering the emerging findings on molecular events at transcriptional, biochemical, hormonal and metabolite levels, we have just begun to decipher the underlying ripening mechanisms in climacteric and non-climacteric fruits. Even when it seems that the role of ethylene in ripening of climacteric and non-climacteric fruits has been elaborated, our knowledge in understanding the roles of other phytohormones in fruit ripening processes is in infancy. Also, upstream regulators required to switch on ethylene production are not yet identified. Higher PAs (SPD and SPM) have been implicated in delaying fruit ripening and simultaneously enhancing fruit nutritional quality attributes. In contrast to detailed elucidation of signaling cascades of all plant hormones, PA signaling pathways and their underlying action mechanisms are not known. Tomato genome studies strongly implicate an epigenetic layer of control for fruit ripening. During fruit ripening, post-translational modifications of histones also influences expression of fruit ripening-related genes. Decrease in DNA cytosine methylation seems to be required to enhance accessibility of ripening regulators to bind target sites and modulate expression of regulatory networks involved in fruit ripening. High-throughput sequencing techniques should be utilized to go beyond model systems and elucidate variation, structure and dynamics of epigenetics in commercial crops. Since fruit quality traits in most of the domesticated or intensively bred commercial crops have less allelic variation, epigenetic-based approaches may be efficiently utilized to improve fruit quality attributes. Understanding of fruit ripening biology including molecular mechanisms and physiology have enabled the use of artificial ripening agents in commercial supply chains, but legal aspects of artificial fruit ripening must be comprehensively considered to avoid future risks.