Author
 |
Smith, David |
|
Abbott, Judith |
|
Gross, Kenneth |
|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/9/2002 Publication Date: 8/20/2002 Citation: N/A Interpretive Summary: Approximately 20% of all fresh produce is never consumed due to losses that occur after harvest. These losses amount to over $6 billion per year. Much of this loss can be attributed to change in texture during storage. Because of the critical relationship that deleterious changes in texture have to quality and postharvest shelf-life, we are studying the mechanisms involved in the loss of firmness that occurs during fruit ripening. Although fruit softening may involve a number of mechanisms, it is generally accepted that genetically-programmed changes in the cell wall (sugar envelope surrounding plant cells) are critical. Several enzymes have been identified in tomato fruit which can alter the cell wall. These enzymes are called beta-galactosidases, and each is encoded for by one corresponding gene. Using molecular genetics we were able to suppress the mRNA abundance of the gene TBG4 (antisense) and it's corresponding exo- galactanase enzyme. In transgenic tomato plants with significantly attenuated TBG4 mRNA levels, the fruit were as high as 40% firmer than control fruit. This implicates an important role for the TBG4 product in tomato fruit softening and may lead to the development of tomato lines with significantly firmer fruit while still maintaining other favorable eating characteristics. This will benefit the fresh produce industry and all consumers by increasing the loss of texture, and therefore the storage life, of fruits and vegetables. This will result in a diminished loss of fresh produce after harvest. Technical Abstract: Transcript abundance of the gene encoding beta-galactosidase II, a beta- galactosidase/exo-galactanase (EC 3.2.1.23) present during tomato ripening was suppressed by expression of an antisense TBG4 cDNA (CaMV35S promoter). RNA gel blot analysis was used to evaluate TBG4 mRNA levels in transgenic fruit. All of the antisense lines had attenuated TBG4 mRNA levels. However TBG4 mRNA suppression was unstable, and mRNA levels varied in ripe fruit among the lines. Suppression of TBG4 mRNA levels in antisense fruit was correlated with a reduction in exo-galactanase activity against a lupin galactan. All of the antisense lines had reduced free galactose levels at mature green stage 4, but levels comparable to controls during ripening. Total cell wall galactosyl content in antisense fruit was not different from control fruit. Whole fruit firmness was measured using a texture analyzer, and the means of the peak force measurements for four out of six antisense lines were higher than control fruit. One line had ripe fruit that were 40 percent firmer than controls. These fruit also had the lowest TBG4 mRNA and exo-galactanase levels and the highest wall galactosyl content during early ripening, implicating an involvement of this gene product in cell wall modification leading to fruit softening. |
