Overexpression of Osmyb4 enhances compatible solute accumulation and increases stress tolerance of Arabidopsis thaliana

In this paper we report the metabolic and molecular changes in response to cold and drought induced in Osmyb4 transgenic Arabidopsis thaliana compared to the wild-type. The rice Osmyb4 gene codes for a transcription factor (Myb4) induced by cold treatment and, in Arabidopsis transgenic plants, improves cold and freezing tolerance (Vannini et al. 2004). Here we report the ability of Myb4 to induce also drought tolerance in Arabidopsis transgenic plants. By the use of Nuclear Magnetic Resonance (NMR) and enzymatic assays, we showed that several compatible solutes (glucose, fructose, sucrose, proline, glycine betaine and sinapoyl malate) accumulate in higher amount in Osmyb4 overexpressing plants with respect to the wild-type, both under normal and stress conditions. Considering proline, we also found that in transgenic plants the levels of the mRNAs coding for ƒ´ƒ¡-pyrroline¡V5-carboxylate synthase (P5CS; EC not assigned) and for ƒ´1-pyrroline-5-carboxylate dehydrogenase (P5CDH; EC 1.5.1.12) were higher and lower, respectively. The constitutive activation of several stress-inducible pathways and different kinetics in the accumulation of several metabolites, in Myb4 transgenic plants, may represent an advantage to prepare plants to face the stress condition. Moreover, these results taken together suggest that Myb4 integrates the activation of multiple components of stress response.