Ethylene and developmental signals regulate expression of lipoxygenase genes during tomato fruit ripening

Introduction The role of ethylene in regulating the expression of Tomato fruit ripening involves complex gene expression three lipoxygenase (LOX) genes TomloxA, TomloxB and and biochemical changes which ultimately result in alteraTomloxC during fruit ripening has been investigated. tions to the physical properties of the fruit giving rise to The study used a combination of low-ethylene fruit changes in colour, texture, flavour, and aroma (Grierson containing an ACC oxidase (ACO1) sense-suppressing and Schuch, 1993; Gray et al., 1994). Ethylene synthesis transgene and tomato fruit ripening mutants deficient increases at the onset of tomato ripening and transgenic in ethylene perception in the case of Never-ripe (Nr) experiments have clearly demonstrated that the synthesis or ripening in the case of the ripening-inhibitor (rin). and perception of this hormone is required for the full The results indicate that the three genes are differentidevelopment of the ripening process (Oeller et al., 1991; ally regulated during fruit ripening and that a combinaPicton et al., 1993a; Wilkinson et al., 1997). Ethylene tion of ethylene and developmental factors influence acts to promote the transcription and translation of their expression. The expression of TomloxA declines numerous ripening-related genes, including those involved during ripening and this is delayed in the ACO1 transin cell wall breakdown and carotenoid biosynthesis (Gray genic low-ethylene and Nr fruit indicating that this et al., 1994). phenomenon is ethylene regulated. However, tranSeveral pleiotropic ripening mutants have been identiscript abundance also declines during rin fruit develfied that affect multiple aspects of the ripening process opment indicating that developmental factors also (Gray et al., 1994). The ripening-inhibitor (rin) mutant is influence the expression of TomloxA. TomloxB expresone of the best characterized of these and also displays sion increases during fruit ripening and expression one of the strongest phenotypes. The fruit lacks the usual is increased by ethylene as reduced accumulation is climacteric rise in ethylene production, remains firm and evident in transgenic and mutant fruit. The same ethyeventually turns yellow-green due to impaired lycopene lene up-regulated and ripening-related expression is production (Tigchelaar et al., 1978). rin fruit show altered shown by TomloxC, however, expression increases in expression of a number of ripening-related mRNAs rin fruit at the onset of colour change, indicating that (Lincoln and Fischer, 1988; Knapp et al., 1989; Picton et there may also be a developmental component regulatal., 1993b), they also retain the capacity partially to ing TomloxC expression. These results indicate that respond to ethylene although they do not ripen fully individual LOX isoforms are differentially regulated following ethylene treatment (Herner and Sink, 1973; and may have distinct functions during tomato fruit Lincoln and Fischer, 1988; Picton et al., 1993b; Yen et ripening. al., 1995). In contrast, the Never-ripe (Nr) mutant displays ethylene insensitivity (Lanahan et al., 1994; Yen et al.,