Increasing Omega-3 Desaturase Expression In Tomato Results In Altered Aroma Profile And Enhanced Resistance To Cold Stress

Abstract

One of the drawbacks in improving the aroma properties of tomato fruit is the complexity of this organoleptic trait with a great variety of volatiles contributing to determine specific quality features. It is well established that the oxylipins hexanal and (Z)-hex-3-enal, synthesized through the lipoxygenase pathway, are among the most important aroma compounds and impart in a correct proportion some of the unique fresh notes in tomato. Here, we confirm that all enzymes responsible for the synthesis of these C6 compounds are present and active in tomato fruit. Moreover, due to the low odor threshold of (Z)-hex- 3-enal, small changes in the concentration of this compound could modify the properties of the tomato fruit aroma. To address this possibility, we have over-expressed the ω-3 fatty acid desaturases FAD3 and FAD7 that catalyzed the conversion of linoleic (18:2) to linolenic acid (18:3), the precursor of hexenals and its derived alcohols. Transgenic OEFAD tomato plants exhibit altered fatty acid composition with an increase in the 18:3/18:2 ratio in leaves and fruits. These changes provoke a clear variation in the C6 content that results in a significant alteration of the (Z)-hex-3-enal/hexanal ratio that is particularly important in ripe OE-FAD3FAD7 fruits. In addition to this effect on tomato volatile profile, OE-FAD tomato plants are more tolerant to chilling. However, the different behavior of OE-FAD plants underscores the existence of separate FA fluxes to ensure plant survival under adverse conditions.