Structural Diversity and Distribution of Nuclear Matrix Constituent Protein Class Nuclear Lamina Proteins in Streptophytic Algae.

Nuclear matrix constituent proteins in plants function like animal lamins, providing the structural foundation of the nuclear lamina and regulating nuclear organization and morphology. Although they are well characterized in angiosperms, the presence and structure of nuclear matrix constituent proteins in more distantly related species, such as streptophytic algae, are relatively unknown. The rapid evolution of nuclear matrix constituent proteins throughout the plant lineage has caused a divergence in protein sequence that makes similarity-based searches less effective. Structural features are more likely to be conserved compared to primary amino acid sequence; therefore, we developed a filtration protocol to search for diverged nuclear matrix constituent proteins based on four physical characteristics: intrinsically disordered content, isoelectric point, number of amino acids, and the presence of a central coiled-coil domain. By setting parameters to recognize the properties of bona fide nuclear matrix constituent protein proteins in angiosperms, we filtered eight complete proteomes from streptophytic algae species and identified strong nuclear matrix constituent protein candidates in six taxa in the Classes Zygnematophyceae, Charophyceae, and Klebsormidiophyceae. Through analysis of these proteins, we observed structural variance in domain size between nuclear matrix constituent proteins in algae and land plants, as well as a single block of amino acid conservation. Our analysis indicates that nuclear matrix constituent proteins are absent in the Mesostigmatophyceae. The presence versus absence of nuclear matrix constituent protein proteins does not correlate with the distribution of different forms of mitosis (e.g. closed/semi-closed/open) but does correspond to the transition from unicellularity to multicellularity in the streptophytic algae, suggesting that a nuclear matrix constituent protein-based nucleoskeleton plays important roles in supporting cell-to-cell interactions.