Investigating the Role of the Collagen Protein in Trichodesmium erythraeum

Collagen molecules are structural in nature and primarily found in eukaryotic, multicellular organisms. The collagen protein family is diverse and its membership is continually expanding as new collagen-like molecules are identified. Although previously believed to be limited to eukaryotes, collagen-like proteins have been identified in various prokaryotic organisms. Identification of collagen in unicellular eukaryotes and prokaryotes has opened discussion on the function of these collagens and their role in the emergence of multicellularity. Recently, a collagen-like gene was identified in the marine cyanobacterium, Trichodesmium erythraeum. T. erythraeum is a colonial, filamentous cyanobacterium found in tropical and subtropical oligotrophic oceans. Based on the known function of collagen proteins, it was hypothesized that the collagen protein encoded in the T. erythraeum genome functioned to provide structural integrity for normal growth and survival of T. erythraeum. The collagen protein, named TrpA, was found to be both transcribed and translated at all phases of growth though there is a marked increase in transcription during the logarithmic phase, and a significantly increased amount of protein expressed during both the logarithmic and stationary phase. Immunofluorescent labeling of the TrpA protein revealed that the collagen protein is expressed in the septa between cells along the filament. Additionally, TrpA can be seen localizing to the division septa forming during intercalary cell division. Collagenase treatment of T. erythraeum trichomes exhibited fragmentation of the cells along the filament. Using phylogenetic analysis, structural modeling and circular dichroism, it was confirmed that the protein being expressed belongs to the collagen family, specifically exhibiting characteristics of non-fibrillar collagens. Scanning electron microscopy revealed that TrpA is also being expressed entirely on the surface of the trichomes. While working towards developing a TrpA knockout, it was revealed that T. erythraeum is likely naturally transformable. Based on the results found in this study, it is clear that the collagen protein identified in the genome of T. erythraeum is involved in maintaining cell-cell adhesion of the cells along the filament. The expression of TrpA on the surface of trichomes indicates that this protein may also be involved in the adherence of trichomes within a colony.Ph.D., Biological Sciences -- Drexel University, 201

The TrpA protein of Trichodesmium erythraeum IMS101 is a non-fibril-forming collagen and a component of the outer sheath

Collagen molecules are structural in nature and primarily found in eukaryotic, multicellular organisms. Recently, a collagen-like protein, TrpA, was identified and characterized in the marine cyanobacterium Trichodesmium erythraeum IMS 101, and it was shown to be involved in maintaining the structural integrity of the trichomes. The TrpA protein contains one glycine interruption in the otherwise perfectly uninterrupted collagenous domain. In this study, we used phylogenetic analysis to determine that the TrpA protein sequence is most closely associated with non-fibril-forming collagen proteins. Structural modelling and circular dichroism data suggest that the glycine insertion decreases the stability of TrpA compared to uninterrupted collagen sequences. Additionally, scanning electron microscopy revealed that TrpA is expressed entirely on the surface of the trichomes, with no specific pattern of localization. These data indicate that the TrpA protein is part of the outer sheath of this organism. As such, this protein may function to promote adhesion between individual T. erythraeum trichomes, and between this organism and heterotrophic bacteria found in the same environment

A plausible mechanism, based upon SHORT-ROOT movement, for regulating the number of cortex cell layers in roots

Formation of specialized cells and tissues at defined times and in specific positions is essential for the development of multicellular organisms. Often this developmental precision is achieved through intercellular signaling networks, which establish patterns of differential gene expression and ultimately the specification of distinct cell fates. Here we address the question of how the SHORT-ROOT (SHR) proteins from Arabidopsis thaliana (AtSHR), Brachypodium distachyon (BdSHR), and Oryza sativa (OsSHR1 and OsSHR2) function in patterning the root ground tissue.We find that all of the SHR proteins function as mobile signals in A. thaliana and all of the SHR homologs physically interact with the AtSHR binding protein, SCARECOW (SCR). Unlike AtSHR, movement of the SHR homologs was not limited to the endodermis. Instead, the SHR proteins moved multiple cell layers and determined the number of cortex, not endodermal, cell layers formed in the root. Our results in A. thaliana are consistent with a mechanism by which the regulated movement of the SHR transcription factor determines the number of cortex cell layers produced in the roots of B. distachyon and O. sativa. These data also provide a new model for ground tissue patterning in A. thaliana in which the ability to form a functional endodermis is spatially limited independently of SHR. (Résumé d'auteur