The simultaneous suppression of tomato polygalacturonase and expansin reduces the susceptibility of ripe fruits to Botrytis cinerea

CANTU D., VICENTE A.R., DEWEY F.M., BENNETT A.B., LABAVITCH J.M., POWELL A.L.T.1

California USA

Conferencia; American Society of Plant Biologists Western Section Annual Winter Meeting; 2007

American Society of Plant Biologists

Tomato fruit ripening involves developmental changes leading to ripe, palatable and soft fruit. However, ripening also leads to increased susceptibility to pathogens. Excessive softening and postharvest diseases are the major factors limiting postharvest storage and distribution of fruit. The cell wall (CW) provides a physical barrier against pathogen penetration and host tissue colonization. Fruit softening has been associated largely with the digestion of CW polysaccharides (CWs). To determine whether CW breakdown is significant in the ripening-associated increase in fruit susceptibility, fruit from transgenic tomato lines with suppressed expression of the fruit ripening-associated polygalacturonase (PG) and/or expansin (LeExp1) were evaluated. The simultaneous suppression of PG and LeExp1 (-PG-Exp) led to a dramatic reduction in the susceptibility to Botrytis cinerea, a significant tomato postharvest pathogen, whereas the suppression of either PG or LeExp1, alone, did not result in any change in susceptibility. In -PG-Exp fruit, pectin solubililization and depolymerization were reduced and the fruit remained firmer than the untransformed controls or the single -PG or LeExp1 transgenic lines. Cell wall swelling, a typical change that occurs during ripening, also was reduced in -PG-Exp fruits as observed by electron microscopy and in vitro experiments. When total CW polysaccharides were added as carbon sources for liquid cultures of B. cinerea, growth was 3 fold greater on CWs from control wild type fruit than on CWs from -PG-Exp fruit, suggesting a direct effect of fruit CW composition/integrity on vigor of fungal growth. Future work will determine whether inducible defenses also are involved in the restriction of B. cinerea development observed on fruit from the transgenic lines. These results show that the functions provided by the expression of PG and LeExp1 together contribute to the susceptibility of ripe fruit to B. cinerea and that the simultaneous suppression of these two genes represents an effective approach to reduce postharvest losses.