Summary


The PsEND1 is an anther-specific gene from pea that displays very early expression in anther primordium cells. We fused the PsEND1 promoter region to the cytotoxic barnase gene to induce specific ablation of cell layers where the PsEND1 is expressed and consequently produces male sterile plants. Expression of the chimaeric PsEND1::barnase gene in two tomato cultivars with agronomical/commercial interest produced male-sterile flowers and parthenocarpic fruits. This observation suggests that early male-sterility in tomato is related to the induction of parthenocarpic fruits.
The application of GA biosynthesis inhibitors (paclobutrazol) to PsEND1::barnase ovaries blocked fruit growth and fruit-set, an effect that was reversed by the application of GA3.
We have analized the fruit production and fruit quality of the transgenic lines obtained in three cultivars: Micro-Tom, p73 and Moneymaker. In general, fruits from transgenic plants showed smaller weight and size compared to control fruits but these transgenic lines produce more fruits per plant than the control. Therefore, total fruit production of all transgenic genotypes was similar to the control ones.
Parthenocarpic transgenic fruits showed higher soluble solids content (ºBrix) but similar or lower titratable acidity than control fruits. The ratio soluble solid content/ titratable acidity has been used as an index of the flavour of fruits; a high ratio was correlated with a sweet taste. The index flavour was higher in all transgenic fruits so the transgenic fruits might have better flavour than control ones.
Volatile profiles of transgenic fruits were very different from control fruits. Transgenic fruits showed more abundant volatiles derived from a diverse set of lipid, carotenoid and phenolic compounds than the control lines. These compounds have been described to provide a floral, frutal and fresh aroma. These changes suggest that parthenocarpic fruits have more organoleptic value than control ones.
Other phenolics compounds and volatiles derivated from phenylalanine, leucine and isoleucine were less abundant in the transgenic lines. These compounds have been correlated with the descriptors “green tomato” or “grassy” and contribute negatively to tomato flavour. Thus, a reduction of these compounds could be a positive aspect of the transgenic fruits.
We analyzed primary metabolites of two genotypes with a particularly striking difference in the profile of volatiles. The results showed that these transgenic lines have more content of all analyzed amino acids and sugars than control ones. These changes suggest that parthenocarpic fruits have more organoleptic value and better taste than control ones.
On the other hand the development of the PsEND1::barnase ovary has been analyzed at transcriptome level to study the link between parthenocarpic fruit set and male-sterility in tomato. Our results suggest that the ovary development in PsEND1::barnase plants is similar to the one in the pollinated ovary. In the stage 1 (5-6 days before anthesis) we have identified 1.940 genes differentially regulated compared to control genotype were identified. Many of these genes are involved in metabolism, regulation and transport of auxins and gibberellins. These results show the implication of auxins and gibberellin in the early fruit set in PsEND1::barnase tomato plants.
At stage 1, the analysis of genes related with GAs biosynthesis and deactivation shows that transcript levels of SlGA20ox1, SlGA3ox1, SlGA2ox1 and SlGA2ox4 were higher in transgenic ovaries than control ones. Besides the expression of genes related auxins such as SlIAA9 and SlARF7 were lower in transgenic ovaries than control ovaries at stage 1. Also, we have identified some MADS-box transcription factors.

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