Molecular Biology of Fruit Ripening

Aims

Provide a detailed knowledge of ethylene physiology in plants, and its role in developmental processes with particular emphasis on fruit ripening. Analyze the processes and the mechanisms involved in ethylene biosynthesis, perception and signal transduction. Provide a general knowledge and information of the ripening syndrome of fleshy fruit and the role of ethylene in controlling this developmental stage. Describe the main processes, in particular at molecular level,  characterizing fruit ripening and relate them with the evolution of the extrinsic and intrinsic parameters used to monitor quality at harvest and during storage Describe the relationship between the gaseous hormone and the expression of ripening-related genes (ethylene-dependent and ethylene-independent pathways). Provide specific and detailed information about the pathways of both primary and secondary metabolic ripening-related processes and describe  the effects of ethylene and its inhibitors on the regulation of these pathways Analyze the postharvest factors affecting fruit metabolism and ethylene physiology in relation to the goal of prolonging commercial and shelf life of the produce

Prerequisites

Biochemistry, Plant Physiology, Plant Molecular biology,  Cell and Molecular Biology, Molecular biology techniques.

Learning Outcomes

After completing the unit, students will be able to:   Describe the role of ethylene in plants. Define the different processes occurring in plant tissues concerning ethylene biosynthesis, perception and signal trasnduction Ananlyze and evaluate  the different processes and changes characterizing the ripening syndrome of fleshy fruit, with particular emphasis on ethylene-dependent processes Relate the quality parameters of fruit at harvest and during storage to the underlying molecular and biochemical mechanisms Support and understand  decisions concerning harvest and post-harvest strategies and identify the effects of technical solutions on ripening-related processes. Identify and judge the critical points in quality management of different fruit commodities Demonstrate their ability in evaluating ripening-related technical and  scientific issues Apply their knowledge to formulate hypotheses and set up applied research protocols in the field of fruit ripening and storage Communicate with appropriate descriptions and terms the specific issues and subject matters described in the unit.  

Syllabus

Molecular Biology of Ethylene and  Fruit Ripening course contents. Ethylene is the gaseous plant hormone and it is involved in controlling events throughout the life cycle of plants. This growth regulator plays important roles in several processes, such as seed germination, tissue (roots and shoots) growth, cell separation, senescence, plant-pathogen interactions, and fruit ripening. A bulk of information is now available concerning processes and regulatory mechanisms related to the biosynthesis of the hormone, the receptors effective in binding ethylene, and several steps of the transduction system. Although most of the dicoversies have been obtained using the model species Arabidopsis and its mutants,  important advancements have been the result of specific studies carried out in fleshy fruit tissues, in particular in tomato. In climacteric fruit, ripening is  charcaterized by the increase in respiration and ethylene production.  Fruit ripening is a developmentally- and hormonally-regulated process that encompasses a wide range of cellular changes including fruit softening, chlorophyll degradation, pigment production, aroma development etc.  A detailed knowledge of the molecular regulation of both  the ethylene production and  perception mechanisms as well as the signal transduction pathways has allowed a better comprehension of the relationship between this hormone and the typical changes occurring in ripening fruit.  This is particularly true in tomato, where the existence of a plethora of ripening mutants, detailed genetic maps and common transformation protocols have made this species the model system for genetic, molecular and biochemical studies of fruit ripening. Besides ethylene physiology, emphasis will be given to biochemical and molecular aspects of primary metabolic processes (respiration), cell wall  modifications, secondary metabolisms such as pigmentation changes and aroma compound production during ripening and in relation to different storage conditions affecting general metabolism (including ethylene physiology). Genomics and system biology approaches will be described and results, in a context of  a comparative approach, discussed and analyzed to identify common and divergent key molecular components of the ripening syndrome in climacteric and non-climacteric species.

Content Delivery

Considering the background (see prerequisites) of the students attending the Unit and the topics of the Unit, the delivery of the component will be done through lectures as a typical University course Power point presentations will be used. The Unit will be divided in 4 different modules: Module 1- Introduction. Ethylene as the gaseous plant hormone: the hormone biosynthesis and the signalling pathways. Module 2:  Fruit ripening as a genetically-regulated syndrome and the biology  of ethylene in climacteric fruit. Module 3- Primary and secondary metabolisms and the changes occurring during fruit ripening. Module 4:   -Storage effects on molecular events and biochemical pathways of fruits.  All these aspects will be discussed mostly at biochemical and molecular level.

Coursework And Assignment Details

The coursework of this unit involves a combination of the following:   - Group work report:  (30%) - Individual written examination (70%)     Group work report During the week students will be assembled in 3-4 groups each selecting one fruit crop (or genetically similar fruit crops) . Based on literature search and scientific papers each group will produce a  written report (review, max 10 pages) on Ripening physiology of the selected crop or species group.   Assessment criteria - Up to date references and complete bibliographic search - Evidence of involvement in all group work - Clear, concise and rational written presentation   Individual written examination. It will consist in two parts: A) Multiple choice and B) essay.   A)   Multiple choice (40%). Students will be asked to answer 15 specific questions or statements concerning topics discussed during the week course B)   Essay (60%). Students will appropriately describe and analyze a specific ripening-related process discussed during the week course   Assessment criteria - Appropriate scientific language and description of the biochemical and molecular events characterizing the specific process -  Demonstration of a detailed and broad knowledge of the process in a general view of the ripening syndrome and the storage procedures.