The Nuclear Localization of the DnaJ-Like Zinc Finger Domain-Containing Protein EDA3 Affects Seed Development in Arabidopsis thaliana.

The DnaJ-like zinc finger domain-containing proteins are involved in different aspects of plastid function and development. Some of these proteins were recently reported to have dual subcellular localization in the nucleus and plastids. One member of this family, PSA2 (AT2G34860), was found to localize to the thylakoid lumen and regulate the assembly of photosystem I (PSI). However, PSA2 was also annotated as Embryo sac Development Arrest 3 (EDA3) from the observation that its embryo sac development was arrested at the two-nuclear stage. In this study, we characterized the eda3 mutant, and demonstrated that, as compared with the wild-type (WT) plants, the mutant has shorter siliques, fewer siliques per plant, and fewer seeds per silique. Both aborted and undeveloped ovules were observed in siliques of the mutant. By immunoblot analysis, we found that, different from the chloroplast localization in mature leaves, EDA3 localizes in the nucleus in seeds. A nuclear localization signal was identified from the deduced amino acid sequence of EDA3, and also proved to be sufficient for directing its fusion peptide into the nucleus.

Autofluorescence-Free Immunoassay Using X-ray Scintillating Nanotags.

Autofluorescence background in complex biological samples is a major challenge in achieving high sensitivity of fluorescence immunoassays (FIA). Here we report an X-ray luminescence-based immunoassay for high-sensitivity detection of biomarkers using X-ray scintillating nanotags. Due to the weak scattering and absorption of most biological chromophores by X-ray excitation, a low-dose X-ray source can be used to produce intense scintillating luminescence from the nanotags for autofluorescence-free biosensing. To demonstrate this concept, we designed and synthesized NaGdF4:Tb@NaYF4 core/shell nanoparticles as kind of high-efficiency X-ray scintillating nanotags, which are able to convert high-energy X-ray photons to visible light without autofluorescence in biological samples. Notably, strong X-ray absorption and minimized surface quenching arising from the heavy Gd3+/Tb3+ atoms and core/shell architecture of the nanoparticles were found to be critically important for high-efficiency X-ray excited luminescence for high-sensitivity biosensing. Our method allows for sensing alpha-fetoprotein (AFP) biomarkers with a detection limit down to 0.25 ng/mL. Moreover, the as-described X-ray luminescence immunoassay exhibited an excellent biological specificity, high stability, and sample recovery, implying an opportunity for applications in complex biological samples. Consequently, our method can be readily extended for multiplexing sensing and medical diagnosis.

At3g53630 encodes a GUN1-interacting protein under norflurazon treatment.

Chloroplasts are semi-autonomous organelles, with more than 95% of their proteins encoded by the nuclear genome. The chloroplast-to-nucleus retrograde signals are critical for the nucleus to coordinate its gene expression for optimizing or repairing chloroplast functions in response to changing environments. In chloroplasts, the pentatricopeptide-repeat protein GENOMES UNCOUPLED 1 (GUN1) is a master switch that senses aberrant physiological states, such as the photooxidative stress induced by norflurazon (NF) treatment, and represses the expression of photosynthesis-associated nuclear genes (PhANGs). However, it is largely unknown how the retrograde signal is transmitted beyond GUN1. In this study, a protein GUN1-INTERACTING PROTEIN 1 (GIP1), encoded by At3g53630, was identified to interact with GUN1 by different approaches. We demonstrated that GIP1 has both cytosol and chloroplast localizations, and its abundance in chloroplasts is enhanced by NF treatment with the presence of GUN1. Our results suggest that GIP1 and GUN1 may function antagonistically in the retrograde signaling pathway.