Rice transglutaminase gene: Identification, protein expression, functionality, light dependence and specific cell location

Transglutaminases (TGases), that catalyze post-translational modification of proteins, are scarcely known in plants. As part of a project to characterize transglutaminase genes in new plant species, the identification and characterization of a TGase in rice is presented. Using differential primers, a cDNA (tgo) of 1767 bp from genomic rice DNA amplification was obtained. The primers were designed from the rice DNA sequence relatively homologous to the gene encoding active maize chloroplast TGase. Amino acid sequence of the deduced rice TGase protein (TGO) indicated that it contains the enzyme catalytic triad (Cys–His–Asp), three repeats, myristoylation domains and a leucine zipper motif. The TGO recombinant protein was characterized, showing specific activity regulation, and indicating that tgo encoded for an authentic TGase. Substrate preference and Ca2+ dependent activity were also detected. In the rice plant TGO protein was immunolocalized in the grana chloroplasts, in protein vesicles near them, and in the bulliform cells. Immunoblot analyses, tgo mRNA expression, and TGase activity indicated that TGO expression in rice was light dependent and regulated by the illumination period. This work increases significantly our plant TGase understanding. Its functional role in rice, which is a good model system for C3 plants, is discussed.This study was supported by the Spanish projects MEC BFU2006-15115-01/BMC and BFU2009-08575. N. Campos has a pre-doctoral fellowship from the Agencia Española de Cooperación Internacional para el Desarrollo (AECID). The authors would especially like to thank Marc Boix (CRAG Microscopy Services), Oriol Casagran (CRAG Genomic Services), N. Cortadellas (Serveis Cientifico-Tècnics, UB), and the CRAG Greenhouse Services for their technical assistance and S. Burgess for the English correction. The authors would also like to thank the Spanish Ministry of Science and Innovation, Consolider-Ingenio 2010 Programme. CSD2007-00036 “CRAG” and Xarxa de Referencia en Biotecnologia of the Generalitat de Catalunya.Peer reviewe