To Fall or Not to Fall, that's the Question! Molecular Mechanisms Underlying Organ Abscission in Citrus

During their life cycle, citrus plants can experience different processes involving separation of cells by dissolution of cell adhesion materials and breakdown of cell walls at specific sites on the plant body. Abscission enables both vegetative and reproductive organs to be shed in response to developmental, hormonal and environmental cues. From an evolutionary point of view, abscission is a highly favorable process that has several advantages such as fruit and seed dispersal as well as the shedding of no longer needed, infected, damaged or senescent organs. In an agricultural context, however, abscission is a major limiting factor for crop productivity. In this regard, understanding the regulation of abscission is an important phenomenon for the citrus fruit industry. A deeper understanding of the mechanisms underlying abscission would help to regulate crop production and improve current cultural and management practices such as mechanical harvesting of fruit or removal of undesirable excess fruit production. In addition, further molecular research on abscission could help to elucidate new molecular markers to improve genetic breeding. This review highlights the current status of research on genes specifically associated with organ abscission that have been uncovered so far in citrus.