HOS15 represses flowering by promoting GIGANTEA degradation in response to low temperature in Arabidopsis

Flowering is the primary stage of the plant developmental transition and is tightly regulated by environmental factors such as light and temperature.However,the mechanisms by which temperature signals are integrated into the photoperiodic flowering pathway are still poorly understood.Here,we demonstrate that HOS15,which is known as a GI transcriptional repressor in the photoperiodic flowering pathway,controls flowering time in response to low ambient temperature.At 16℃,the hos15 mutant exhibits an early flowering phenotype,and HOS15 acts upstream of photoperiodic flowering genes(GI,CO,and FT).GI protein abundance is increased in the hos15 mutant and is insensitive to the proteasome inhibitor MG132.Furthermore,the hos15 mutant has a defect in low ambient temperature-mediated GI degradation,and HOS15 interacts with COP1,an E3 ubiquitin ligase for GI degradation.Phenotypic analyses of the hos15 cop1 double mutant revealed that repression of flowering by HOS15 is dependent on COP1 at 16℃.However,the HOS15-COP1 interaction was attenuated at 16℃,and GI protein abundance was additively increased in the hos15 cop1 double mutant,indicating that HOS15 acts independently of COP1 in GI turnover at low ambient temperature.This study proposes that HOS15 controls GI abundance through multiple modes as an E3 ubiquitin ligase and transcriptional repressor to coordinate appropriate flowering time in response to ambient environmental conditions such as temperature and day length.

The A/ENTH Domain-Containing Protein AtECA4 Is an Adaptor Protein Involved in Cargo Recycling from the trans-Golgi Network/Early Endosome to the Plasma Membrane

Endocytosis and subsequent trafficking pathways are crucial for regulating the activity of plasma membrane-localized proteins. Depending on cellular and physiological conditions, the internalized cargoes are sorted at （and transported from） the trans-Golgi network/early endosome （TGN/EE） to the vacuole for degradation or recycled back to the plasma membrane. How this occurs at the molecular level remains largely elusive. Here, we provide evidence that the ENTH domain-containing protein AtECA4 plays a crucial role in recycling cargoes from the TGN/EE to the plasma membrane in Arabidopsis thaliana. AtECA4：sGFP primarily localized to the TGN/EE and plasma membrane （at low levels）. Upon NaCI or mannitol treatment, AtECA4：sGFP accumulated at the TGN/EE at an early time point but was released from the TGN/EE to the cytosol at later time points. The ateca4mutant showed higher resistance to osmotic stress and more sensitive to exogenous abscisic acid （ABA） than the wild type, as well as increased expres- sion of ABA-inducible genes RD29A and RD29B. Consistently, ABCG25, a plasma membrane-localized ABA exporter, accumulated at the prevacuolar compartment in ateca4, indicating a defect in recycling to the plasma membrane. However, the role of AtECA4 in cargo recycling is not specific to ABCG25, as it also functions in the recycling of BRII. These results suggest that AtECA4 plays a crucial role in the recycling of endocytosed cargoes from the TGN/EE to the plasma membrane.

Plant-based,adjuvant-free,potent multivalent vaccines for avian influenza virus via Lactococcus surface display

Influenza epidemics frequently and unpredictably break out all over the world,and seriously affect the breeding industry and human activity.Inactivated and live attenuated viruses have been used as protective vaccines but exhibit high risks for biosafety.Subunit vaccines enjoy high biosafety and specificity but have a few weak points compared to inactivated virus or live attenuated virus vaccines,especially in low immunogenicity.In this study,we developed a new subunit vaccine platform for a potent,adjuvant-free,and multivalent vaccination.The ectodomains of hemagglutinins(HAs)of influenza viruses were expressed in plants as trimers(tHAs)to mimic their native forms.tHAs in plant extracts were directly used without purification for binding to inactivated Lactococcus(iLact)to produce iLact-tHAs,an antigen-carrying bacteria-like particle(BLP).tHAs BLP showed strong immune responses in mice and chickens without adjuvants.Moreover,simultaneous injection of two different antigens by two different formulas,t^(HAH5N6+H9N2) BLP or a combination of t^(HAH5N6) BLP and t^(HAH9N2) BLP,led to strong immune responses to both antigens.Based on these results,we propose combinations of plant-based antigen production and BLP-based delivery as a highly potent and cost-effective platform for multivalent vaccination for subunit vaccines.