Variants of this TGase have been expressed recombinantly in Escherichia coli and tgz-transplastomic tobacco plants engineered. Here we use Th-T and CR binding, Fourier Transformed Infrared Spectroscopy and Transmission Electronic Microscopy to study the conformational properties of the protein deposits formed by maize transglutaminase in vitro and in the chloroplasts of transplastomic plants, demonstrating that in both cases they exhibit characteristic amyloid features. Homoplasmic tobacco tgz-transgenic plants presented abnormal phenotype with respect to the leaf colour. The TGZ protein was immunolocalized into chloroplast inclusion bodies, suggesting that in the plant the protein is present in an at least partially aggregated state, which might coexist with functional conformations as shown for bacterial inclusion bodies. The thylakoids in the chloroplasts of non-transgenic plants displayed a normal arrangement with grana stacks consisting of 15–20 tightly appressed thylakoid membranes interconnected by stroma thylakoids. We analyzed the protein content of the soluble and insoluble fractions of transgenic plants by SDS-PAGE and Western Blot using an anti-TGZ antibody to determine if TGZ is effectively found in an aggregated state in vivo. In spite of the much higher protein content of the soluble fraction, TGZ is absolutely absent in this fraction and localizes exclusively into the insoluble fraction, in which constitutes a major protein component. Three different types of TGZ bands are detected by Western Blot in the insoluble fraction upon SDS-denaturation: a first band corresponding to a truncated species, according to its smaller size when compared with purified TGZ, a second band corresponding to the full length monomeric protein and several intense high molecular bands corresponding to SDS-resistant aggregated species. This SDS-resistant species resemble the oligomeric species found in aggregated solutions of amyloid proteins like Ab-peptide. Like in the case of amyloid assemblies, in addition to SDS, high chaotropic reagent concentrations are required to disrupt these aggregated species, indicating that they are stabilized by strong intermolecular interactions. To analyze if the aggregates formed by TGZ in transplastomic tobacco plants display amyloid features similar to those observed in vitro we isolated the protein insoluble fraction. The same amount of WT tobacco plant leaves were fractionated and analyzed Silmitasertib simultaneously as a negative control. The ATR FT-IR spectrum in the amide I region of transplastomic aggregates is significantly different from that of WT aggregates. The spectrum of transplastomic aggregates is dominated by an intermolecular bsheet whereas that of WT plants.