Summary

The most relevant feature of the tomato insertional mutant Arlequín is the homeotic conversion of sepals into fleshy fruit-like organs. Genetic analysis indicated that the mutant phenotype co-segregated with the T-DNA insertion and was inherited as a monogenic semi-dominant trait. 
Morphological, structural and metabolic analysis showed that Arlequín sepals have an inherent capacity to change their development program and become fleshy fruit-like organs. Scanning electron microscopy (SEM) analysis indicated that the epidermal cells of sepals exhibit features of carpel cells, and histological analysis showed that cells from the inner part of the succulent sepals are indistinguishable from those the fruit pericarp. These changes in cell identity are accompanied by in-depth metabolic alterations. Water absorption, accumulation of dry matter and saccharolytic activity, with the subsequent accumulation of glucose and fructose, suggest that the mutant sepals turn into organs that can act as a sink, as it normally occurs with true tomato fruits. In addition climacteric ethylene production occurred in normally transformed sepals, as happens in tomato fruits, and the red color in transformed sepals is explained by synthesis of lycopene at a similar level to that of WT fruit, indicating that Arlequín sepals undergo a process of maturation.
Interestingly, the conversion of sepals into fruit-like organs is not always synchronized with fruit development and that process can even occur in the absence of fruit setting. This indicates that the Arlequín calyx can compete and act as an independent and alternative sink to the true fruit.
In Arlequín homozygous plants the change in the style ablation zone promotes a change in fruit shape. In these plants, both true fruit and sepals are transformed into fleshy fruit-like organs that exhibit exceptional quality traits for fresh consumption and in particular for industrial processing: greater levels of sugars and lycopene, and almost twice the solid soluble content than in wild type fruits. In addition, Arlequín mutation confers an additional advantage because the fruit abscission zone is inhibited thus facilitating mechanical harvesting.
Molecular characterization showed that developmental changes affecting Arlequín sepals are caused by an ectopic expression of ARLEQUÍN (ALQ) / TAGL1 MADS-box gene, due to the insertion of a truncated T-DNA in a transcriptional regulatory domain of the tagged gene. Functional analysis of ALQ gene provided evidence that the tagged gene not only plays an important role in the ripening process, but also plays a crucial role in fruit set and early fruit development.
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Conclusiones	 159






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