(98) Molecular Analysis of Abscission Layer Activation in Apple Fruit Pedicels

Abstract

Abscission of leaves, floral organs, and fruit is a developmentally and environmentally regulated process initiated in specialized thin layers of cells within abscission zones (AZs). Very little is known about early molecular events that drive abscission, especially of fruit. Commercial apple production relies on the use of flower and fruit abscission-promoting and -inhibiting compounds to enhance fruit quality, control preharvest fruit drop, and maintain consistent annual bearing. The success of chemical treatments is strongly influenced by numerous factors, including environment, genotype, developmental stage of the fruit, and physiological state of the tree. Toward developing improved strategies for regulating fruit abscission, we carried out transcriptional profiling of competent-quiescent and activated abscission layers. We found that a decisive event in the sequential process of abscission layer development is the transcriptional activation of the MdPEL1 gene, encoding a plant pectate lyase protein and potentially involved in the degradation of the middle lamella of adjacent abscission layer cells. Additionally, regulatory elements of at least 12 homologous pectate lyase genes in Arabidopsis thaliana were found to direct expression in floral AZs and in dehiscence zones along valve margins, suggesting that these genes have evolutionary conserved function. This work identifies a novel role for pectate lyases in plants. Furthermore, many abscission-related genes identified in this study are being used to track biochemical and regulatory pathways that participate in abscission in response to chemical treatments or environmental effects.