Ethylene synthesis during grapevine berry ripening

Ethylene is a plant hormone involved in several developmental processes as well as in responses to biotic and abiotic stresses. It is synthesized from S-adenosyl-L- methionine by the action of two enzymes, namely ACC synthetase (ACS) and ACC oxidase (ACO), encoded by multigenic families. Although Vitis vinifera is not classified as a climacteric species, there are evidences of ethylene playing a role in berry ripening. In order to shed light on ethylene biosynthesis during this developmental program we measured its content in planta and characterized the ACS and ACO isoforms likely involved in this pathway. The high sensitivity of laser photoacustic spectroscopy allowed to detect a small but significant peak of ethylene in ‘Pinot Noir’ clusters few days before véraison. An homology search of the ACS and ACO genes in the Pinot Noir genomes based on Arabidopsis and tomato amino acids sequences identified nine putative ACS and 19 ACO genes. The sequences have been classified and compared to those of Arabidopsis and tomato by phylogenetic analysis to identify the major monophyletic groups. Four ACS genes and three ACO isoforms were the most expressed along fruit ripening. Among these, two ACS and two ACO isoforms showed a highly correlated expression and are currently being studied to better define their role during berry development.