Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824
Performing Department
HORTICULTURE
Non Technical Summary
The biochemical changes that occur during fruit ripening impart desirable characteristics upon an otherwise inedible immature fruit. These include changes in color, the accumulation of sugars, altered texture and increased production of flavor and aroma compounds. These changes serve as quality determinants for the consumer. However, the shelf life of fruits is notoriously short and the quality enhancements that are brought about by ripening are short lived as the fruit over-ripens and deteriorates. This project aims to investigate the genetic mechanisms that control fruit ripening and quality. An enhanced understanding of the ripening process at the molecular level will provide information that may be useful for breeding new crops that have extended shelf life and increased quality.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Fruits are an essential component of the human diet providing sources of carbohydrates, vitamins, minerals and antioxidants. These nutritional attributes are only realized following a wide array of biochemical changes that serve to convert an inedible unripe fruit into a fruit that is nutrient rich and palatable. Fleshy fruits are highly diverse although there are evolutionary conserved changes that accompany ripening in many species including changes in color, increased softening, accumulation of sugars and the production of aroma compounds. The commonality of these processes suggest that there are underlying genetic mechanisms that regulate ripening in diverse species. One signal that has been shown to influence ripening in many species is the plant hormone ethylene. Inhibition of ethylene synthesis or action results in delayed fruit ripening in a subset of important fruit crop species known as the climacteric fruits, which includes apple, peach, banana and tomato,
proving that ethylene is a positive regulator of the ripening process. The positive nutritional influence that ripening imparts upon fruits is quickly offset by their short shelf life which leads to losses in quality and ultimately senescence and deterioration. Therefore the window of palatability for the consumer is often quite brief. The highly perishable nature of fleshy fruits leads to a range of agricultural and postharvest processes that are designed to maximize shelf life. Often fruits are picked unripe when they are more amenable to handling and transport and are then stored for extended periods and ripened artificially just prior to marketing. These practices require a tremendous energy input and add to the cost of food production but also lead to fruits that have reduced quality in terms of their nutritional profile and organoleptic properties. An understanding of the biochemical changes that occur during ripening and how they are regulated will provide information that can
be used to select crop varieties that have enhanced quality attributes including increased shelf life with reduced energy input, greater nutritional status and consumer satisfaction. The objective of this project is to further our understanding of the mechanisms that regulate quality and ripening of fleshy fruit.
Project Methods
Tomato is an excellent model system for investigating ripening processes. Many landmark studies that have defined the forefront of research into the mechanisms of fruit ripening have been achieved using tomato as a model species. Compared with many fleshy fruit bearing crops tomato has a short life cycle, a compact growth habit and diploid genetics. It is amenable to transformation by Agrobacterium tumefaciens, allowing hypotheses concerning gene function to be readily tested. There is also an extensive collection of resources for genomic scale biology, including an emerging genome sequence and a bioinformatics platform that are all within the public domain. As a direct consequence of its amenable genetics, there is a large and varied germplasm collection that contains monogenic mutants and stable populations generated through diverse crosses to wild tomato species. The depth of the germplasm collection has allowed a large number of loci that influence fruit ripening
and quality to be identified at the genetic level. Through genetic analysis some of the genes responsible for conferring mutant phenotypes and natural allelic variation that impact ripening and quality in tomato have been identified, however the vast majority have not. This project will utilize two approaches that have the fundamental aim of linking genotype to phenotype. The first approach will focus on identifying genes that impact fruit ripening and quality through forward genetics based upon mutant phenotype and positional cloning strategies to identify candidate genes. The validity of these candidates will be assessed to confirm that the correct loci have been identified. I have previously used this approach to successfully identify the genetic basis of four loci in tomato and under this project I have three additional loci that are potential targets for genes that impact fruit quality. Of the loci already cloned, two alter aspects of the biology of the hormone ethylene, a third
alters the timing to the onset of ripening and a fourth alters fruit quality. The second approach undertaken in this proposal will be to functionally characterize the genes that I have already identified through positional cloning efforts. Three of these genes do not have associated in vivo biochemical functions and a series of experiments will be performed using transgenic, molecular and biochemical approaches to address their potential functions in plants. Through translational research it is possible that the genes and processes discovered under this project may be amenable to study in other fruit and horticultural crops.