BIANCIOTTO, VALERIA , ISABELLA MARTINI & PAOLA BONFANTE.
Centro di Studio Micologia del Terreno (CNR) and Dipartimento di Biologia Vegetale, Università di Torino, V.le Mattioli 25, 10125 - Torino, ITALY.
In order to obtain a durable and broad-spectrum resistance
against plant pathogens current strategies consist in trasforming plants with
genes coding for antimicrobial proteins of plants, animal or microbial origin.
An obvious concern is that increased levels of these antimicrobial compounds
affect not only the target pathogen, but also beneficial micro-organisms such
as mycorrhizal fungi, rhizobia and other micro-organisms promoting plant growth.
We focussed on the effects of transgenic plants expressing a plant antifungal
protein on AM fungi. In particular, we have investigated whether transgenic
plants expressing antifungal defensin proteins allow the development of mycorrhizal
symbiosis. Plant defensins are small cistein-rich peptides of about 45 amino-acids
and transgenic tobacco plants expressing the defensin Rs-AFP2 show an enhanced
resistance to the foliar pathogen Alternaria longipes. (Terras et al.,
The Plant Cell 7:573-588, 1995). In order to know whether such enhanced
gene expression could also affect root colonization by symbiotic fungi, a number
of transgenic lines of Nicotiana tabacum, expressing defensins at either
low or high level, have been tested for their ability to develop AM.
Our experiments show that all the seedlings were infected, irrespectively of
the expression level. No difference in the percentage of mycorrhization was
found. Light and transmission electron microscopy did not reveal any conspicuous
difference in the structure of hyphae, vesicles, and arbuscules in any of the
transgenic plants tested. Consequentely, enhanced resistance to pathogens conferred
by the constitutive expression of defence-related genes does not seem to interfere
with the symbiotic potential of plants.
Key words: AM fungi, transgenic plants, defensins.