Over-expression of maize transglutaminase in tobacco chloroplasts

Abstract

Transglutaminases (TGases) are intracellular and extra cellular enzymes that catalyze post-translational modification of proteins by establishing ¿-(¿-glutamyl) links and covalent conjugation of polyamines. The results of this activity are the modification of the protein conformation and the formation of high molecular weight conjugates. The interest of these enzymes is focussed on its applications in clinical trials (there are implicated in neurodegenerative diseases, blood coagulation, etc.), food additives (texturing agents), wool textiles, biopolymers, etc. As part of a project aiming to characterize the role of maize plastidial transglutaminase (chlTGZ) in the plant chloroplast and the effect of TGZ heterologous over-production, this paper presents the effect of the over-expression of tgz gene from maize, the first plant transglutaminase cloned (Torne et al. 2003, Villalobos et al. 2004), in tobacco chloroplasts via plastid transformation. With this technique, the transgene is integrated in the plastid genome via homologous recombination. In the present work, the increase in TGase activity (four times in transplastomic plant leaves) induced in the tgz-transformed tobacco plants resulted in enhanced polyaminylation of thylakoid proteins and in increased thylakoid stacking (Ioannidis et al. 2009). Moreover, the over-expressed chlTGZ protein, accumulated progressively in chloroplast inclusion bodies like in E. coli cells (Carvajal et al. 2007). This accumulation was accompanied by oxidative stress symptoms, thylakoid scattering, membrane degradation and reduction of thylakoid interconnections in the old leaves (Ortigosa et al. 2010). Consequently, the electron transport between photosystems decreased. In spite of these alterations, transplastomic plants can be maintained and reproduced in vitro. These results are discussed in line with chlTGZ involvement in chloroplast functionality and TGase production in chloroplasts.