Investigating the role of ethylene signal transduction and gene regulation during tomato fruit development and ripening

Ethylene plays an important regulatory role in climacteric fruit ripening. Recent discoveries in both tomato and Arabidopsis have resulted in isolation and characterization of genes regulating ethylene biosynthesis and perception. In Arabidopsis, all ethylene responses characterized to date are regulated by the negative regulatory putative MAP kinase kinase kinase encoded by the CONSTITUTIVE TRIPLE RESPONSE1 ( CTR1) gene. In this study, isolation and characterization of a tomato CTR-like gene, TCTR1 are reported. TCTR1 was isolated from a breaker stage ripening fruit cDNA library followed by RACE-PCR to recover a full-length cDNA. TCTR1 is homologous to CTR1 and other RAF kinases. An mRNA splicing variant of TCTR1 (TCTR1v) with a 69 bp in-frame deletion was observed at low frequency. TCTR1 is expressed in multiple tissues and is induced during fruit ripening and by ethylene. Over expression of TCTR1 in transgenic plants resulted in fruit specific effects including delayed and incomplete fruit ripening. Another TCTR1 like sequence TCTR3, was isolated. TCTR3 shows constitutive expression in all tissues examined. Data presented here suggest that tomato fruit may have evolved to limit CTR1 levels and there may be functional redundancy in other tissues.; In a separate set of experiments, differential display was used to isolate novel genes that are regulated by ethylene and/or developmental signals early in tomato fruit ripening. We obtained full-length or near full-length cDNA sequences for three of these differential display tomato fruit ripening clones (DDTFR). DDTFR8 has sequence homology to a mammalian steroid hormone receptor. DDTFR8 is fruit ripening specific and ethylene regulated. DDTFR10/A is homologous to ethylene responsive element binding proteins (EREBPs), and is induced by ethylene and during fruit ripening. DDTTR18 is another ripening regulated, fruit specific gene whose function is not yet known. The expression and sequence analysis of DDTFR8 and DDTFR10/A indicate roles of putative hormone signal transduction components involved in fruit ripening which have not been previously characterized.