Fruit cell wall enzymes as targets for biotechnology.

SOZZI GO; PEDRO MARCOS CIVELLO

Genetic Resources and Biotechnology

Regency Publications

Lugar: New Delhi; Año: 2005; p. 214 - 249

Almost one decade has passed since the Flavr SavrTM tomato (an antisense polygalacturonase fruit) became the first genetically engineered fresh product reaching the market place (Redenbaugh et al., 1994). As the range of fruits produced by transgenic plants continues to broaden, cell wall enzymes that function in the disassembly, modification and turnover of cell wall polysaccharides have become one of the most important targets for engineering. Plants over- and underexpressing different enzymes have been used to delineate the catalytic effects they have during the fruit ripening process (Giovannoni, 2001). In this chapter, we highlight many of the advances in the identification of the relevant genes and gene products that either have been or could be manipulated to alter cell wall structures and the rate of fruit softening. Texture is a major fruit attribute which has a great effect on consumer perception of fruit quality. Different factors affect fruit textural properties, among them cell wall polysaccharide composition (Harker et al., 1997; Barrett et al., 1998). In the last fifteen years, different aspects of cell wall structure and metabolism during fruit growth, ripening and softening, and the impact of altered gene expression and cell wall enzyme activity on fleshy fruit texture, have been extensively reviewed (Gross, 1990; Giovannoni et al., 1991; Fischer and Bennett, 1991; Fry, 1995; Seymour and Gross, 1996; Cosgrove, 1997, 1998, 1999; 2000a, 2000b; Hadfield and Bennett, 1998; Rose and Bennett, 1999; Dumville and Fry, 2000; Brummell and Harpster, 2001; Giovannoni, 2001). Cell wall enzyme activity changes during growth and ripening have only been partially elucidated during the last three decades by the synergistic use of many disciplines, including plant physiology, biochemistry, chemistry and genetics. Nevertheless, the most powerful tool has been transgenic technology which has provided insights into the cell wall enzyme actions by altering the expression of genes involved in the synthesis of those enzymes. There is a great deal of interest in down-regulating the presence and action of different cell wall enzymes, given that high activity levels may trigger or enhance fruit softening. Success in improving fruit textural qualities will depend on our understanding of how these enzymes interact with their substrates in the complex wall matrix of fruit tissue to determine the mechanical properties of the walls in individual cells as well as in the more complex fruit organ.