Physiogenomics of pear ripening

Christopher Arthur Hendrickson

Among agricultural crops, climacteric fruit quality is strongly influenced by respiratory and ethylene biosynthetic activity throughout development and postharvest management. Many economically important climacteric and nonclimacteric-ripening species lie within this class. Additionally, climacteric fruits harbor phenotypic variability in autocatalytic ethylene biosynthesis and ripening induction in response to cold-temperature exposure. These fruit also exhibit significant variability in recovery from application to the ethylene signaling inhibitor 1-methylcyclopropene, with apple (Malus × domesticaBorkh.) fruit predictably recovering from treatments, while pear (Pyrus communis L.). Control and regulation of this variability among Rosales fruit remains unclear. Understanding causal molecular and genetic underpinnings of these phenomenon in pear fruit can accelerate crop improvement and postharvest management efforts. Research in this dissertation addresses this fundamental knowledge gap by: (1) Reviewing known physiology and regulatory points in cold- and ethylene signal transduction and biosynthesis in fleshy fruits. Release of genomics tools and information in these species has allowed for direct interrogation of novel genetic underpinnings of unique horticultural traits, such as cold-dependent ripening or variable 1-MCP recovery; (2) Comparative physiogenomics analysis of gene expression among pear hormonal and environmental signaling-related pathways during conditioning and ripening. By applying a nonparametric spatial-reduction analysis, differential expression between Anjou and Bartlett varieties was identified. These genes provide candidate regulatory control points in cold-induced regulation of System 2 ethylene biosynthesis and ripening in pear; and (3) Pathway-targeted ripening compounds' influence on ripening processes in whole and sliced pear fruit. Experimental compounds were identified from prior comparative physiogenomics analysis in pear that accelerate ethylene production and ripening proceses in whole and sliced pear. While variable, some results indicate this influence can mitigate 1-MCP-induced inhibition of ripening. From prior work, these compounds are thought to directly stimulate activity of a pathway which exhibited differential expression in Bartlett and Anjou fruit in response to cold-temperature exposure. This mode of action leverages a previously underutilized means of affecting fruit ripening, and may allow for improved control of whole and sliced pear fruit throughout postharvest management. Finally, a summary of important findings and future directionsfrom this work will be presented.

Physiogenomics of pear ripening

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