Premature abscission of flowers and fruits triggered by low light stress can severely reduce crop yields. However, the underlying molecular mechanism of this organ abscission is not fully understood. Here, we show that a gene (SlCLV3) encoding CLAVATA3 (CLV3), a peptide hormone that regulates stem cell fate in meristems, is highly expressed in the pedicel abscission zone (AZ) in response to low light in tomato (Solanum lycopersicum). SlCLV3 knockdown and knockout lines exhibit delayed low light-induced flower drop. The receptor kinases SlCLV1 and BARELY ANY MERISTEM1 function in the SlCLV3 peptide-induced low light response in the AZ to decrease expression of the transcription factor gene WUSCHEL (SlWUS). DNA affinity purification sequencing identified the transcription factor genes KNOX-LIKE HOMEDOMAIN PROTEIN1 (SlKD1) and FRUITFULL2 (SlFUL2) as SlWUS target genes. Our data reveal that low light reduces SlWUS expression, resulting in higher SlKD1 and SlFUL2 expression in the AZ, thereby perturbing the auxin response gradient and causing increased ethylene production, eventually leading to the initiation of abscission. These results demonstrate that the SlCLV3-SlWUS signaling pathway plays a central role in low light-induced abscission by affecting auxin and ethylene homeostasis.

Exosomes are membrane-enclosed extracellular vesicles derived from cells, carrying biomolecules that include proteins and nucleic acids for intercellular communication. Owning to their advantages of size, structure, stability, and biocompatibility, exosomes have been used widely as natural nanocarriers for intracellular delivery of theranostic agents. Meanwhile, surface modifications needed to endow exosomes with additional functionalities remain challenging by their small size and the complexity of their membrane surfaces. Current methods have used genetic engineering and chemical conjugation, but these strategies require complex manipulations and have only limited applications. Herein, we present an aptamer-based DNA nanoassemblies on exosome surfaces. This in situ assembly method is based on molecular recognition between DNA aptamers and their exosome surface markers, as well as DNA hybridization chain reaction initiated by an aptamer-chimeric trigger. It further demonstrated selective assembly on target cell-derived exosomes, but not exosomes derived from nontarget cells. The present work shows that DNA nanostructures can successfully be assembled on a nanosized organelle. This approach is useful for exosome modification and functionalization, which is expected to have broad biomedical and bioanalytical applications.

Exosomes are extracellular vesicles (50-100 nm) circulating in biofluids as intercellular signal transmitters. Although the potential of cancerous exosomes as tumor biomarkers is promising, sensitive and rapid detection of exosomes remains challenging. Herein, we combined the strengths of advanced aptamer technology, DNA-based nanostructure, and portable electrochemical devices to develop a nanotetrahedron (NTH)-assisted aptasensor for direct capture and detection of hepatocellular exosomes. The oriented immobilization of aptamers significantly improved the accessibility of an artificial nucleobase-containing aptamer to suspended exosomes, and the NTH-assisted aptasensor could detect exosomes with 100-fold higher sensitivity when compared to the single-stranded aptamer-functionalized aptasensor. The present study provides a proof-of-concept for sensitive and efficient quantification of tumor-derived exosomes. We thus expect the NTH-assisted electrochemical aptasensor to become a powerful tool for comprehensive exosome studies.

Laboratory in vitro evolution (LIVE) might deliver DNA aptamers that bind proteins expressed on the surface of cells. In this work, we used cell engineering to place glypican 3 (GPC3), a possible marker for liver cancer theranostics, on the surface of a liver cell line. Libraries were then built from a six-letter genetic alphabet containing the standard nucleobases and two added nucleobases (2-amino-8H-imidazo[1,2-a][1,3,5]triazin-4-one and 6-amino-5-nitropyridin-2-one), Watson-Crick complements from an artificially expanded genetic information system (AEGIS). With counterselection against non-engineered cells, eight AEGIS-containing aptamers were recovered. Five bound selectively to GPC3-overexpressing cells. This selection-counterselection scheme had acceptable statistics, notwithstanding the possibility that cells engineered to overexpress GPC3 might also express different off-target proteins. This is the first example of such a combination.