Signals for Gene Expression in Ripening Tomato Fruit

Abstract

cDNA clones for a number of mRNAs expressed in ripening tomato fruit have been characterised (Grierson et al., 1986a; Maunders et al., 1987; Holdsworth et al., 1987; Ray et al., 1987, 1988). One of these (pTOM 6) has been shown by DNA and protein sequence analysis to encode the enzyme polygalacturonase (PG) (Grierson et al., 1986b), which is synthesised de novo during ripening (Tucker and Grierson, 1982) and is involved in the solubilisation of the pectin fraction of fruit cell walls. cDNA clones for PG have also been isolated by a number of other groups (DellaPenna et al., 1986; Sheehy et al., 1987; Lincoln et al., 1987). Ethylene stimulates the accumulation of ripening-related mRNAs (Maunders et al., 1987) and PG mRNA is inhibited by silver ions (Davies et al., 1988), which are thought to interfere with ethylene perception or action. Production of PG and, to a lesser extent, other mRNAs is substantially reduced in the tomato ripening mutants rin and Nr (DellaPenna et al., 1987; Knapp et al., 1989), and is also inhibited in normal fruit at 35°C (Picton and Grierson, 1988).