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

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.51

AN AUXIN-REPORTER GENE DETECTS ALTERED IAA CONTENTS IN TOMATO FLORAL MUTANTS

M. ROSSI*, R. CACCIA*, F. SALAMINI**, A. MAZZUCATO*, G.P. SORESSI*

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

**) Max-Planck-Institut für Züchtungsforschung, Carl-von-Linné Weg 10, 50829 Köln, Germany

tomato, auxin, floral mutants, reporter genes

Auxin is involved in the control of several growth and developmental processes in plants. Notwithstanding this importance, the molecular mechanisms underlying auxin action are to date poorly understood. The characterization of mutants, whose phenotype is putatively determined by altered hormone levels or perception, may shed light on the role played by hormones in different aspects of plant developmental biology, physiology, biochemistry and molecular biology. In this perspective, the tomato is a favoured experimental species, since more than one thousand monogenic mutants have been described to date that cover all aspects of plant growth and development.

In this research, the auxin accumulation dynamic has been analysed in a number of tomato floral mutations by means of a reporter construct where the auxin-inducible promoter of the Agrobacterium tumefaciens gene 5 was cloned upstream of the uidA gene (GUS). The mutants selected for the analyses were: uniflora (uf, that bears inflorescences reduced to a single flower), lateral suppressor (ls, that, besides the lack of lateral shoots, also shows lack of the corolla segments), stamenless 2 (sl-2, that shows homeotic conversion of stamens into carpels), fasciated (f, that shows flowers with supernumerary stamens and carpels) and parthenocarpic fruit-2 (pat-2, that under cold nights and incresing photoperiod shows autonomous ovary growth and parthenocarpic fruit production). All the mutants where crossed with plants harbouring the reporter construct in homozygosis and F₂ families were screened for the presence of the transgene. From kanamicin - resistant wild-type (WT) and mutant plants segregating in the F₂ families, plants organs (roots, leaves, petals, stamens, ovaries and fruits) were collected and subjected to the histochemical GUS assay. Non transgenic specimens, used as negative control, were always devoid of reporter signal. In turn, remarkable, organ-specific differences were reported between mutant and WT plant tissues.

WT roots showed strong auxin accumulation at the root tip and at the adventitious root primordia. The uf, sl-2 and f mutants showed no difference from the WT at the root level. Differently, pat-2 and ls roots showed a lower IAA content. Signal intensity was also overall associated to root vigour. In leaf tissues, for the WT and all mutants the signal was absent or very weak, with the exception of sl-2 that showed higher IAA content.

The WT ovary showed an increasing auxin content through its development into fruit, up to a maximum that was reached at the mature green stage. While the uf ovary did not show any difference from the WT, pat-2 and f ovaries and their young fruits had a stronger reporter signal, in agreement with the putative role of the hormone in parthenocarpic development and in organ number specification. However, auxin content in the pat-2 ovary was lower than in the WT at later stages of fruit development, as it was in the partially sterile ls mutant; such observation supports the hypothesis that fruit IAA is essentially contributed by the seeds.

The reported results on auxin distribution in tomato WT and floral mutant plants confirm the important role played by this hormone in regulating flower and fruit development and growth.