How does ionizing radiation affect amyloidogenesis in plants?

Ionizing radiation is a harsh environmental factor that could induce plant aging. We hypothesized that radiation-related aging remodels proteome, particularly triggering the accumulation of prion-like proteins in tissues. The object of this study, pea (Pisum sativum), is an agriculturally important legume. Research on the functional importance of amyloidogenic proteins was never performed on this species. Pea seeds were irradiated by 50 Gy of X-rays. Afterwards, Fourier-transform infrared spectroscopy (FTIR) was used to investigate changes in the secondary structure of proteins in germinated seedlings. Specifically, we evaluated the ratio between the amide I and II peaks. Next, we performed protein staining with Congo red to compare the presence of amyloids in the samples. In parallel, we profiled detergent-resistant proteome fraction by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS). Differentially accumulated proteins were functionally analyzed in MapMan software, and the PLAAC tool was used to reveal putative prion-like proteins. We showed a reduced germination rate, yet higher plant height and faster appearance of reproductive organs in the irradiated group compared with the control; furthermore, we demonstrated more β-sheets and amyloid aggregates in the leaves of stressed plants. We detected 531 proteins in detergent-resistant fraction extracted from roots, and 62 were annotated as putative prion-like proteins. Notably, 29 proteins were significantly differentially abundant between the irradiated and the control groups. These proteins belong to several functional categories: amino acid metabolism, carbohydrate metabolism, cytoskeleton organization, regulatory processes, protein biosynthesis, and RNA processing. Thus, discovery proteomics provided deep data on novel aspects of plant stress biology. Our data hinted that protein accumulation stimulated seedlings' growth and affected the regulatory system, primarily through translation and RNA processing. Increased abundance of primary metabolism-related proteins points to more intensive metabolic processes triggered in germinating pea seeds upon X-ray exposure. The functional role of detected putative amyloidogenic proteins should be validated in overexpression or knockout follow-up studies.