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 - 3.27
ALTERED
DEFENSE RESPONSE TO FUSARIUM OXYSPORUM
IN TOMATO (LYCOPERSICON ESCULENTUM,
MILL.) LINES TRANSFORMED WITH ROL
GENES OF AGROBACTERIUM RHIZOGENES
BETTINI
P. *, SANTANGELO E.**, MICHELOTTI S.*, MARVASI M.*, BINDI D.*, MOSCONI P.**,
CRINÒ P.***, BUIATTI M.*
*)
Dipartimento di Biologia animale e Genetica “Leo Pardi”,
Università degli Studi di Firenze
**)
Consorzio Agrital Ricerche, Maccarese (Roma)
***)
ENEA C.R. Casaccia, UTS Biotecnologie, Protezione della Salute Umana e degli
Ecosistemi, Roma
tomato,
rol genes, plant-pathogen interaction, Fusarium oxysporum, phytohormones
The
role of phytohormones in plant defense response to pathogens has been clearly
established, even if evidence
concerning their effect is still controversial. In fact, both an inhibition and
an increase in host resistance to fungi, bacteria and viruses have been
reported after treatment with growth regulators or transformation with genes
involved in auxin and cytokinin biosynthesis (Martinez Noel et al. 2001, Plant
Physiol. Biochem. 39: 815-823; Clarke et al. 1999, Plant Physiol. 120:
547-552; Beckman and Ingram 1994, Physiol. Mol. Plant Pathol. 45:
229-246; Sitbon F et al. 1999, Plant Science 141: 165-173). The aim of
the present study is to analyse the effect of the modification of endogenous
hormone equilibria on the horizontal defense response of plants. For this
purpose, Lycopersicon esculentum cv. Tondino,
kindly provided by Petoseed Italia, has been transformed with Agrobacterium
rhizogenes rolA, B, C, D genes, known to be
involved in the phytohormone metabolic network. The transgenic plants and the
corresponding controls (regenerated, not transformed) have been self-fertilized
and the resulting segregating progenies have been subjected to PCR and RT-PCR
molecular analyses in order to evaluate the presence and the expression of
transgenes, respectively. Cosegregation of an aberrant phenotype with presence
of the transgene was demonstrated for the rolA progeny. This
confirmed that the observed modifications were due to the introgression of the
foreign gene and not to variation induced during the in vitro
regeneration process. The same progenies have been infected in vivo with
the phytopathogenic fungus Fusarium oxysporum f.
sp. lycopersici race 0, in order to assess if the introgression of
the rol genes led to an increased tolerance/resistance to
pathogens. Under controlled conditions, 15-day old plantlets (20/genotype) were
infected by immersion of the rooting apparatus into a fungal suspension (1.5x106
conidia/ml), while 5-10 uninfected plants for each genotype were used as a
positive control. Symptoms were evaluated 15, 27 and 40 days after inoculation.
Preliminary data revealed that rolA transformants
reacted better than rolD, the response of the latter ones being not significantly
different from their untransformed control. In particular, the best response to
the fungus has been recorded for the clone rolA23, harbouring
only one copy of the transgene. Molecular analyses, carried out on a sample of
21 rolA23 plants surviving the infection, has shown a ratio
of 6 transgenic : 1 not transgenic plants, this being higher than the ratio
expected on the basis of a single gene segregation. This finding seems to
support the hypothesis that the highest level of Fusarium resistance
observed could be due to the presence of the foreign gene. The expression of
PR-1 gene, considered to be a marker of Systemic Acquired Resistance (SAR),
will also be analysed quantitatively by real-time PCR in a sample of infected
and symptomless plants, in order to investigate the possible role of this
resistance mechanism in the tolerance of the rolA
plants.
Infection
experiments on the progenies of rolB and rolC
transformants are currently underway.
Research
activity carried out in the frame of the PNR Biotecnologie Avanzate II, tema 4,
coordinated by Consorzio Agrital Ricerche (Chairman: Prof. Gian Tommaso
Scarascia Mugnozza).