Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 3.40

DIFFERENT AUXIN Content in PARTHENOCARPIC (pat mutant) AND NORMAL TOMATOES screened by aN “auxin reporter system”

ROSSI M., CACCIA R., MOSCONI P., MAZZUCATO A., SORESSI G.P.

Dipartimento di Agrobiologia e Agrochimica, Sezione di Genetica, Università degli Studi della Tuscia, Via S.C. de Lellis snc, 01100 Viterbo, Italy

soressi@unitus.it

Agrobacterium tumefaciens, auxin, parthenocarpy, reporter genes, tomato

Auxins, primarily indole-3-acetic acid (IAA), exert control over many important processes in plants including cell division and expansion, vascular tissue differentiation, stem elongation, root initiation, apical dominance, gravitropic and phototropic responses, flowering, fruit ripening, leaf senescence and leaf/fruit abscission. Moreover, IAA is a key factor in fruit set and development; when produced or supplied artificially, it is able to induce fruit development even in absence of fertilization, phenocopying natural parthenocarpic mutants.

To increase our understanding on the role of this hormone in flower and fruit development, we monitored the IAA content in two tomato near-isogenic lines (NILs), one bearing recessive alleles for the parthenocarpic fruit (pat) gene, that confer parthenocarpic behaviour, and the other homozygous wild-type at the same locus (WT). IAA dynamics were followed by means of a reporter construct where the auxin-inducible promoter of the A. tumefaciens gene 5 was cloned upstream of the uidA gene (GUS).

The two NILs were transformed with the reported construct and primary transformants were selfed in order to select T₂ lines with the transgene in homozygous condition. Several plant organs (roots, hypocotyls, receptacles, anthers, ovaries and berries) spanning important developmental stages were collected from the transgenic versions of the two NILs and from control untransformed plants, to be subjected to the histochemical GUS assay. Negative controls were always devoid of GUS signal. In the transformed specimens, GUS staining intensity was visually estimated and the data, averaged over a series of experiments, showed remarkable, organ-specific differences between the two genotypes. In the flower, WT anthers showed a GUS signal stronger than in pat, giving evidence of a higher IAA content. Differently, pat ovaries and young fruits showed IAA contents that were higher than in the WT from the flower bud stage to the completion of the cell division phase of fruit development. Later, the GUS signals was stronger in WT than in mutant fruits. The correlation of this results with the pat mutant phenotypes affecting anthers and ovaries proves the reliability of this analysis system and offers several discussion points about the role of IAA on flower and fruit development.