Vesicular trafficking in abscission zone cells during ethylene-promoted fruit abscission in citrus

Abstract

Abscission is a cell separation process by which plants are able to shed aerial organs. This physiological process proceeds through a breakdown in adhesion between a group of specialized cells that usually differentiate in particular positions of the plant body named abscission zones (AZs). The occurrence of fruit abscission has special relevance in fruit tree crops such as citrus since it may have negative consequences on yield. To identify AZ-specifically expressed genes involved in citrus fruit abscission, we used a combined strategy of laser microdissection and microarray analysis to compare the global expression profiles of calyx abscission zone (AZ-C) cells of citrus fruits and adjacent fruit rind cells during ethylene-promoted fruit abscission. The comparison enabled to identify a set of potentially specific genes including those associated with vesicular transport and intracellular transport vesicles. The first ultrastructural observations on AZ-C cells during fruit abscission (Iwahori and van Steveninck, 1976) showed an increase in rough endoplasmic reticulum profiles and dictyosome stacks with associated vesicles that fused with the plasma membrane to release their contents to the cell wall. In this comparative transcriptomic survey, we highlighted specific over-expression in AZ-C cells of genes belonging to the major transport steps along the secretory and the endocytic pathways of vesicle trafficking. In particular, it is likely that some of the genes identified in this study would represent major candidate genes for further biotechnological approaches aimed at trying to solve or at least mitigate agronomic issues regarding citrus fruit abscission.