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

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Oral Communication Abstract

NEW INSIGHTS INTO THE ROLE OF GIBBERELLINS IN THE DEVELOPMENT OF PARTHENOCARPIC TOMATO OVARIES

OLIMPIERI I., TILESI F., BERALDI D., TESTA G., MAZZUCATO A.

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

mazz@unitus.it

fruit set, gibberellins, Lycopersicon esculentum, parthenocarpy, tomato

Gibberellins (GAs) are involved in most aspects of plant growth and development. Among them, GAs play a key role, together with auxin, in supporting the development of the ovary into fruit after the reproductive process has been successfully accomplished. It has been suggested that natural parthenocarpy, i.e. the production of seedless fruits, may be the result of elevate hormone levels in the ovary in the absence of pollination and fertilisation.

To study genetic and physiological determinants that drive fruit set and early development in parthenocarpic tomato ovaries, we use an experimental system based on genetically parthenocarpic mutants. All the experiments compared the behaviour of two near-isogenic lines: one bears recessive alleles for the parthenocarpic fruit (pat) gene and the other is homozygous wild-type at the same locus (WT). In addition to parthenocarpy, the pat mutant shows several pleiotropic effects, such as early flowering, anther shortness and carpelloidy, aberrant ovule integument development and defective pollen tube guidance. Several approaches have been undertaken, such as treatments with GA₃ and GA-inhibitors, differential display between ovary mRNA populations and expression analysis of genes involved in the GA biosynthetic and signal transduction pathway.

Treatments with GA₃ were able to stimulate the development of parthenocarpic fruits in the WT line, while fruit set in the mutant was not altered. On the contrary, treatments with the GA biosynthetic inhibitor Paclobutrazol completely suppressed parthenocarpy in the pat mutant, where fruit set was severely impaired. Conversely, when Paclobutrazol was given together with GA₃, its inhibitory effect on parthenocarpy was fully counteracted. However, nor GA₃ nor Paclobutrazol were able to restore the WT phenotype in pat mutant floral organs.

From differential display analysis, genes that are responsive to GAs have been identified. Among them, an alcohol dehydrogenase-like sequence, up-regulated in the parthenocarpic ovary before anthesis, shows a specific expression in the first cell layers below the epidermis of the placenta, a tissue that is primarily involved in the early parthenocarpic ovary development.

The strong involvement of abnormal GA levels in the pat mutant phenotype was suggested also by the altered expression levels of genes involved in GA biosynthesis (GA 20-oxydases, GA 3b-hydroxylase) and regulation (SPINDLY). Such expression patterns suggest a putative accumulation of GA₂₀ and a shift of the biosynthesis towards the development of endogenous GA₃, an alteration observed in other parthenocarpic tomato mutants, non allelic to pat.

Our results add some pieces of knowledge to the complicated framework of hormonal signals that regulates fruit set. In perspective, this information may put the basis for engineering parthenocarpy by modifying the expression of plant genes involved in hormone synthesis and perception.