Genomic and Biotechnology of the Fruit GBF

Aroma and Fruit Quality

Christian Chervin, Alain Latche, Jean-Claude Pech, Benoit Van-Der-Rest,

Fruit sensorial quality is defined by multiple factors: colour, brilliance, absence of defects, size, texture and of course flavour. Flavour consists both on the perception in mouth (sweetness, acidity or bitterness) and on the odour, yielded by several volatile compounds. These metabolic compounds have several metabolic origins, more particularly the catabolism of fatty acids, amino acids and carotenoids (see scheme below).

In the Fruit Quality team, we have already started the characterisation of different enzymes involved in aroma biosynthesis.

Alcohol acyl-transferase (AAT) catalyses volatile ester formation from an aliphatic thioester (usually acetyl-CoA) and an alcohol (either aromatic or aliphatic). These esters are often responsible of the flavour scent of several fruits (banana, pear, melon). In melon, we have shown that the accumulation of several AAT isoforms occurs during fruit ripening and is controlled by the hormone ethylene. Although expressed simultaneously, these AAT display different enzymatic properties, particularly its substrate specificity, thus giving an explanation to the ester diversity found in melon. Moreover, this susbstrate specificity relies on specific amino acids and can be modified by targeted mutagenesis.

The ADH multigenic family has received much attention in our laboratory. Two ethylene-dependant ADH were characterised in melon ripening fruits. While the first (CmADH1) is homologue to the well-documented tomato ADH2 involved in the balance between alcohol and aldehyde volatiles, the second ADH (CmADH2) belongs to the short chain alcohol dehydrogenase family which has, up to date, received little attention regarding its involvement in fruit ripening. Exploration of their functionalities is under process.

At last, we are also interested in the characterisation of glycosyl transferases associated with fruit ripening since they control the balance between free volatiles and their precursors which are presumably stored in the vacuole as glycosides or glucose esters.