Plants, as sessile organisms, have evolved complex strategies to cope with adverse environmental conditions. However, crop species have been selected for centuries by humans for traits such as yield and organoleptic features. This selection has been carried out to detriment of other traits, such as the ability to grow under limiting conditions or to resist to pathogen attack. This phenomenon causes severe damages in agriculture, both as yield loss and as deterioration of food-stuffs and harvest quality.
Therefore, one of the main goals of the world agriculture research is the comprehension of the mechanisms of stress tolerance and the identification of genes directly involved in these mechanisms. This is a necessary requirement to obtain plant varieties with an increased tolerance to biotic and abiotic stresses, by means of both traditional and innovative methods.
The stress tolerance is a complex multigenic trait, thus the overexpression of a single gene, among those normally involved in the establishment of the stress tolerance, is not sufficient alone to improve it. In this framework, genes coding for transcriptional factors involved in the stress response are of great interest. In fact, the overexpression of a single gene coding for a transcriptional factor gives rise to an increase of the expression of all its target genes and therefore, to an increase of tolerance.
In our Institute, we isolated and characterized several rice genes which code for Myb transcription factors involved in stress tolerance. In particular, the overexpression of one of them in Arabidopsis thaliana makes plants more tolerant to abiotic (cold, freezing, salinity, drought, UV irradiation, ozone) and biotic (viruses, bacteria, fungi) stresses. The better tolerance of transgenic plants (HE) with respect to the wild type (WT), for some of the above mentioned stresses, is shown in the Figure. The complex response carried out by Myb4 indicates that this factor acts as a crucial knot in the intricate network of the response to environmental stimuli. Moreover, the Myb4 action in A. thaliana, a species distantly related from rice, suggests that the crucial knots of this network are strongly conserved among species. On the basis of this hypothesis, we introduced the Osmyb4 gene in several evolutionarily distant crops such as rice, maize, tomato, Osteospermum, apple, barley. Preliminary results indicate that the better tolerance phenotype can be transferred to agronomically important species.
This finding may lead to the production of crop species with a higher stress tolerance, through either the use of the Osmyb4 gene or the use of innovative breeding, such as the marker assisted breeding.
Growing plants more tolerant to abiotic and biotic stresses could reduce not only the economic damages but also the energy and ecological costs.
Patent: Use of specific Myb genes for the manufacture of transgenic plants tolerant to biotic and abiotic stresses. N. PCT/IB03/02878, 2003
Authors: Immacolata Coraggio1*, Franca Locatelli1, Marcella Bracale2, Candida Vannini2
1) Consiglio Nazionale delle Ricerche - Istituto di Biologia e Biotecnologia Agraria, Milano
2) Università degli Studi dell'Insubria - Dipartimento di Biologia Strutturale e Funzionale, Varese
* corresponding author