cgMT1, a metallothionein-like gene from the actinorhizal tree Casuarina glauca, is induced by wounding, oxidative stress and pathogen.

OBERTELLO, MARIANA; WALL, LG; LAPLAZE, L; AUGUY, F; BOGUSZ, D; FRANCHE, C

Umeå University, Umeå, Suecia

Conferencia; 14th International Meeting on Frankia and Actinorhizal plants.; 2006

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 oxidative 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 Casuarina glauca, a metallothionein-like cDNA named cgMT1 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 in situ 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. When introduced into the model plant Arabidopsis thaliana, PcgMT1-gus was found to be highly expressed in roots. In the aerial part of the plants, reporter gene activity was low and restricted to the leaf and stem vascular systems. Wounding, hydrogen peroxyde, methyl viologen and the pathogen Xanthomonas campestris induced the reporter gene expression whereas heavy metals treatments had no notable effect. Transgenic Arabidopsis plants overexpressing the cgMT1 coding sequence under the control of the 35S promoter were found more susceptible to Xanthomonas than the untransformed plants. These data suggest that cgMT1 could participate in defense against intracellular oxidants.