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 - 1.27

REGULATION OF PATHOGENESIS-RELATED GENES IN TRANSGENIC PLANTS WITH CONSTITUTIVELY ACTIVATED DEFENCE SYSTEMS

F. FIOCCHETTI*, M. TUCCI**, C. CARUSO***, L. BERTINI***, F. SACCARDO*

*) Dipartimento di Produzione vegetale, Università della Tuscia, Viterbo

**) CNR – IGV Istituto di Genetica vegetale, sez. Portici (NA)

***) Dipartimento di Agrobiologia e Agrochimica, Università della Tuscia, Viterbo

PR proteins, PR genes, fungal pathogens, genetic transformation, signal transduction pathways

Plants respond to pathogen challenge by activating defence strategies which include synthesis of “pathogenesis-related” (PR) proteins. Most PR proteins show strong antifungal activity in in vitro assays and possibly exert protective roles in vivo.

In recent years, extensive research has been devoted to elucidating the signal transduction pathways leading to activation of plant defences upon pathogen attack. These studies have been mainly focused on specific host-pathogen interactions, involving the presence of a specific avirulence (Avr) gene in the pathogen and a specific resistance (R) gene in the host. Neverthless, the complex signalling mechanisms finally leading to the activation of the whole array of plant responses to pathogens have been only partially unravelled.

The elucidation of the molecular signals activating PR gene expression could greatly contribute to the general understanding of the signal transduction pathways involved in the plant-pathogen interaction.

To this aim, we have studied the differential expression of PR genes in wild type and transgenic tomato plants constitutively expressing tobacco osmotin, a PR5 defence protein, upon treatments with known inducers of defence genes. Namely, expression of PR1, PR4 and PR5 genes was monitored through RT-PCR at different time points after treatments with salicilyc acid (SA) and its functional analogue acibenzolar-S-methyl (benzo[1,2,3]thiadiazole-7-carbothioic acid S-methyl ester) (BTH).

PR1 expression was induced by BTH at late time points after the treatment (15 days) in transgenic seedlings, while SA did not trigger the expression of PR1 in seedlings of both the transgenic and the wild type at 7, 10 or 15 days after the treatment. Upon SA treatment of detached leaves, expression of PR1 increased in the wild type already after 4 hours, while it was constitutively elevated in the transgenic line.

PR4 expression was induced by BTH but not by SA at 10 and 15 days after the treatment in transgenic and wild type seedlings, while SA triggered PR4 expression at 4 and 24 hours in detached leaves of the same genotypes.

The steady-state levels of PR5 RNA did not change upon treatments with either SA and BTH in transgenic and wild type seedlings at long time points, while they increased in detached leaves within 24 hours from the treatment with SA in both the transgenic and the wild type. As expected, PR5 expression was very high in the transgenic line, since the primers used for the RT-PCR detect also the high constitutive expression of the ectopic PR5 gene.