Strigolactones (SLs) are a group of newly identified plant hormones that control plant shoot branching. SL signalling requires the hormone-dependent interaction of DWARF 14 (D14), a probable candidate SL receptor, with DWARF 3 (D3), an F-box component of the Skp–Cullin–F-box (SCF) E3 ubiquitin ligase complex. Here we report the characterization of a dominant SL-insensitive rice (Oryza sativa) mutant dwarf 53 (d53) and the cloning of D53, which encodes a substrate of the SCFD3 ubiquitination complex and functions as a repressor of SL signalling. Treatments with GR24, a synthetic SL analogue, cause D53 degradation via the proteasome in a manner that requires D14 and the SCFD3 ubiquitin ligase, whereas the dominant form of D53 is resistant to SL-mediated degradation. Moreover, D53 can interact with transcriptional co-repressors known as TOPLESS-RELATED PROTEINS. Our results suggest a model of SL signalling that involves SL-dependent degradation of the D53 repressor mediated by the D14–D3 complex.

Constant surveillance of live poultry markets (LPMs) is currently the best way to predict and identify emerging avian influenza viruses (AIVs) that pose a potential threat to public health. Through surveillance of LPMs from 16 provinces and municipalities in China during 2014-2016, we identified 3,174 AIV-positive samples and isolated and sequenced 1,135 AIVs covering 31 subtypes. Our analysis shows that H5N6 has replaced H5N1 as one of the dominant AIV subtypes in southern China, especially in ducks. Phylogenetic analysis reveals that H5N6 arose from reassortments of H5 and H6N6 viruses, with the hemagglutinin and neuraminidase combinations being strongly lineage specific. H5N6 viruses constitute at least 34 distinct genotypes derived from various evolutionary pathways. Notably, genotype G1.2 virus, with internal genes from the chicken H9N2/H7N9 gene pool, was responsible for at least five human H5N6 infections. Our findings highlight H5N6 AIVs as potential threats to public health and agriculture.

The parathyroid hormone receptor-1 (PTH1R) is a class B G protein–coupled receptor central to calcium homeostasis and a therapeutic target for osteoporosis and hypoparathyroidism. Here we report the cryo–electron microscopy structure of human PTH1R bound to a long-acting PTH analog and the stimulatory G protein. The bound peptide adopts an extended helix with its amino terminus inserted deeply into the receptor transmembrane domain (TMD), which leads to partial unwinding of the carboxyl terminus of transmembrane helix 6 and induces a sharp kink at the middle of this helix to allow the receptor to couple with G protein. In contrast to a single TMD structure state, the extracellular domain adopts multiple conformations. These results provide insights into the structural basis and dynamics of PTH binding and receptor activation.