Postharvest fruit quality of transgenic tomatoes suppressed in expression of a ripening-related expansin

Expansins are proteins that cause cell wall loosening, and are involved in many aspects of cell wall modification during development. In tomato, the expansin gene LeExp1 shows ripening-related accumulation of mRNA and protein, and transgenic silencing of the expression of this gene results in tomato fruit that are significantly firmer than corresponding azygous controls throughout ripening. Examination of postharvest quality characteristics of fruit suppressed in accumulation of LeExp1 protein found that increased firmness resulted in significantly improved fruit integrity during storage at 13 degreesC. Based upon the first appearance of noticeable deterioration, fruit shelf life was extended by 5-10 days, depending upon the packaging. However, the increased firmness of LeExp1-suppressed fruit did not result in increased resistance to the necrophytic pathogens Botrytis cinerea and Alternaria alternata. Juice prepared from LeExp1-suppressed fruit following a microwave break had a soluble solids content (degreesBrix), insoluble solids content (precipitate weight ratio) and serum viscosity similar to controls. Resuspension of the insoluble pelleted particulate material in 15% of the serum produced a thick paste, which allowed estimation of gross viscosity in a Bostwick consistometer. The viscosity of paste from LeExp1-suppressed fruit was 19% greater than that from corresponding azygous controls, presumably due to changes in the insoluble particulate components affecting flow characteristics. No significant effects of the LeExp1 transgene on fruit size or fruit number per plant were noted. The data suggest that fruit suppressed in expression of LeExp1 have improved shelf life and processing properties. 2002 Elsevier Science B.V. All rights reserved.