Submitted to: Trends in Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2004
Publication Date: 7/20/2004
Citation: Adams-Phillips, L., Barry, C., Giovannoni, J.J. 2004. Signal transduction systems regulating fruit ripening. Trends in Plant Science. 9:331-338. Interpretive Summary: Fruit ripening is a unique aspect of plant development with direct implications for a large component of the food supply and related areas of human health and nutrition. Recent advances in ripening research have resulted in initial insights into the molecular basis of conserved developmental signals coordinating the ripening process and suggest sequences related to floral development genes might be logical targets for additional discovery. Recent characterization of hormonal and environmental signal transduction components active in tomato fruit ripening (especially ethylene and light) demonstrate conservation of signaling components but novel gene family size and expression motifs that might facilitate complete and timely manifestation of ripening phenotypes. Emerging genomics tools and approaches are rapidly providing new clues and candidate genes useful in expanding the known regulatory circuitry of ripening.
Technical Abstract: We show that ethylene and light signal transduction play important roles in regulating ripening and nutrient composition of tomato fruit. Ethylene signaling components have been defined in tomato including a CTR1-like gene (LeCTR1) that was shown through complementation of an Arabidopsis ctr1 mutant to function in ethylene signaling. LeCTR1 mRNA is also up-regulated during fruit ripening. Additional CTR genes (LeCTR3 and LeCTR4) have been identified in our studies of tomato. Arabidopsis CTR1 has been assigned to a subclass of MAPKKKs comprised of six similar MAPKKK proteins related to the Raf kinases. Phylogenetic analysis indicated that Arabidopsis CTR1 is more similar to LeCTR1, LeCTR3 and LeCTR4 than to any of the other five members of the Arabidopsis MAPKKK subfamily, supporting the existence of a single CTR in Arabidopsis and multiple CTRs in tomato. Further mining of species-specific sequence databases indicated that the presence of a multi-gene family of likely CTR1 genes is not limited to tomato. Informatics analyses also suggest that ESTs representing candidate EIN2, SIMKK and MAPK6 genes are also present in the tomato fruit EST collections. In contrast to ethylene which is required for completion of most if not all ripening processes in climacteric fruit, the impact of light during fruit ripening appears to be specific to regulation of pigment accumulation. Ripe fruit pigments including carotenoids and flavonoids have antioxidant properties that assist in neutralizing the effects of photo-oxidation while also having nutritional significance to humans.