Characterization of cgMT1, a metallothionein-like gene from the actinorhizal tree Casaurina glauca.

OBERTELLO, M; LAPLAZE, L; AUGUY, F; BOGUSZ, D; FRANCHE, C

Toulouse, Francia

Conferencia; 6th European Nitrogen Fixation Conference.; 2004

Metallothioneins (MT) are a group of low-molecular weight, cystein rich molecules that bind heavy metals. Studies in animals have suggested that MTs play a role in heavy metals homeostasis and detoxification. Some MTs are also involved in oxydative stress tolerance. In plants, MT-like genes have been found in a wide variety of species, but their functions remain poorly understood. From a cDNA library of young actinorhizal nodules of was isolated and characterized. CgMT1 is a class I type 1 MT which encodes a 71-aminoacid long polypeptide and the corresponding gene belongs to a small family. CgMT1 was found highly transcribed in roots and nodules, and hybridization experiments demonstrated that the transcripts were located in the pericycle and in the infected nitrogen-fixing cells of the nodules. To further characterize cgMT1, a 1.2 kb fragment corresponding to the promoter was fused to the ß-glucuronidase reporter gene and transgenic Casuarinaceae plants were analysed. High reporter gene expression was found both in roots and nodules. In the aerial part of the plants, reporter gene activity was low and restricted to the leaf and stem vascular systems, and to the ageing leaves. When introduced into the model plant Arabidopsis thaliana, PcgMT1-gus was found to retain the same non-symbiotic pattern of expression. Wounding and methyl viologen (a potent herbicide that exacerbates O- radicals) induced the reporter gene expression whereas heavy metals treatments had no notable effect. These data suggest that cgMT1 could participate in defense against intracellular oxydants. Sense and antisense experiments are currently in progress to get new insigths in the symbiotic and non-symbiotic functions of cgMT1 in Casuarina.