The troponin complex—consisting of three subunits: troponin C (TnC), cardiac troponin I (cTnI) and cardiac troponin T (cTnT)—plays a key role in the regulation of myocardial contraction. Troponins are preferentially localized in the cytoplasm and bind to myofibrils. However, numerous, albeit scattered, studies have shown the presence of troponins in the nuclei of muscle cells. There is increasing evidence that the nuclear localization of troponins may be functionally important, making troponins an important nuclear player in the pathogenesis of various diseases including cancer and myopathies. Further studies in this area could potentially lead to the development of treatments for certain pathologies. In this review, we collected and discussed recent data on the properties of non-canonically localized cardiac troponins, the molecular mechanisms leading to this non-canonical localization, and the possible functions or pathological effects of these non-canonically localized troponins.

Reversibly glycosylated polypeptides (RGPs) have been identified in many plant species and play an important role in cell wall formation, intercellular transport regulation, and plant–virus interactions. Most plants have several RGP genes with different expression patterns depending on the organ and developmental stage. Here, we report on four members of the RGP family in N. benthamiana. Based on a homology search, NbRGP1-3 and NbRGP5 were assigned to the class 1 and class 2 RGPs, respectively. We demonstrated that NbRGP1–3 and 5 mRNA accumulation increases significantly in response to tobacco mosaic virus (TMV) infection. Moreover, all identified class 1 NbRGPs (as distinct from NbRGP5) suppress TMV intercellular transport and replication in N. benthamiana. Elevated expression of NbRGP1–2 led to the stimulation of callose deposition at plasmodesmata, indicating that RGP-mediated TMV local spread could be affected via a callose-dependent mechanism. It was also demonstrated that NbRGP1 interacts with TMV movement protein (MP) in vitro and in vivo. Therefore, class 1 NbRGP1–2 play an antiviral role by impeding intercellular transport of the virus by affecting plasmodesmata callose and directly interacting with TMV MP, resulting in the reduced viral spread and replication.