The ectopic expression of the rice Osmyb4 gene in transgenic plants increases tolerance to abiotic and biotic stresses

The Osmyb4 rice gene encodes a Myb transcription factor involved in cold acclimation. Its constitutive expression in Arabidopsis thaliana results in improved cold and freezing tolerance. Osmyb4 up-regulated 254 genes, 22% of which encode proteins involved in gene expression regulation and signal transduction, suggesting an upstream role of Myb4 in stress response. Most of the up-regulated genes are known to be involved in tolerance not only to cold, but also to other abiotic and environmental stresses (drought, salt, oxidative stresses). Moreover, a high proportion has known functions in resistance to pathogen attacks. Therefore, we analyzed the biochemical and physiological differences between Osmyb4-expressing and wild-type plants and found increased levels of several amino acids that are involved in stress adaptation, acting as osmolytes, scavengers and/or metabolite precursors. When exposed to different adverse conditions, namely drought, salt, u.v., ozone, viruses, bacteria and fungi, transgenic plants effectively demonstrated improved tolerance/resistance to all these stress conditions, suggesting that Osmyb4 represents a crucial knot in the cross-talk of stress signalling cascades through the activation of multiple components.