SUMMARY Chlorophyll (Chl) degradation is a natural phenomenon that occurs during ripening in many fleshy fruit species, and also during fruit storage. The plant hormone ethylene is a key factor in promoting Chl degradation during fruit storage, but the mechanisms involved in this induction are largely unknown. In this study, an apple (Malus domestica) BEL1‐LIKE HOMEODOMAIN transcription factor 7 (MdBEL7), potentially functioning as a transcriptional repressor of the Chl catabolic genes (CCGs), including MdCLH, MdPPH2 and MdRCCR2, was identified as a partner of the ethylene‐activated U‐box type E3 ubiquitin ligase MdPUB24 in a yeast library screen. Yeast‐two‐hybrid, co‐immunoprecipitation and luciferase complementation imaging assays were then used to verify the interaction between MdBEL7 and MdPUB24. In vitro and in vivo ubiquitination experiments revealed that MdPUB24 functions as an E3 ubiquitin ligase to ubiquitinate MdBEL7, thereby causing its degradation through the 26S proteasome pathway. Transient overexpression of MdPUB24 in apple fruit led to a decrease in MdBEL7 abundance and increased expression of CCG genes, including MdCLH, MdPPH2 and MdRCCR2, as well as greater Chl degradation. Taken together, the data indicated that an ethylene‐activated U‐box type E3 ubiquitin ligase MdPUB24 directly interacts with and ubiquitinates MdBEL7. Consequent degradation of MdBEL7 results in enhanced expression of MdCLH, MdPPH2 and MdRCCR2, and thus Chl degradation during apple fruit storage. Our results reveal that an ethylene‐MdPUB24‐MdBEL7 module regulates Chl degradation by post‐translational modification during apple fruit storage.

Multidrug resistant (MDR) bacterial infection has emerged, raising concerns about untreatable infections, and posing the highest health risks. Antimicrobial peptides (AMPs) are thought to be the best remedy for this problem. Here, we showed biosynthetic microcin J25 (MccJ25) exhibited excellent bactericidal activity against standard and clinically relevant veterinary MDR strains with high stability, no cytotoxicity, and no increase in drug resistance. Analysis of antimicrobial mechanism possessed by sensitive enterotoxigenic Escherichia coli (ETEC) based on electron microscopy and Sytox Green methods was carried out. Results showed excellent activity against ETEC was due to permeabilizing bacterial membranes and strong affinity. MccJ25 exhibited high endotoxin-neutralizing activity in both in vivo and in vitro environments, and mice exposed to lipopolysaccharide (LPS) showed decreased plasma LPS levels and improved survival after administration of MccJ25. In an LPS-treated mouse septicemia model, MccJ25 treatment significantly alleviated inflammatory responses by inhibiting proinflammatory factor secretion and expression. In a mouse E. coli infection model, administration of MccJ25 effectively improved host defense against clinically source cocktail of multidrug-resistant E. coli strains induced intestinal inflammation and bacteria dissemination. Results of studies on anti-inflammatory mechanisms showed that MccJ25 downregulated nuclear factor kappa B kinase and mitogen-activated protein kinase, thereby reducing the production of toll-like receptor 4, myeloid differentiation factor 88 and decreasing the key proinflammatory cytokines. These findings clarify MccJ25 may be an ideal antibacterial/antiendotoxic drug candidate that has the potential to further guide the development of anti-inflammatory and/or antimicrobial agents in the war against MDR bacterial infection.

Maintaining ovarian steroidogenesis is of critical importance, considering that steroid hormones are required for successful establishment and maintenance of pregnancy and proper development of embryos and fetuses. Investigating the mechanism that butyrate modulates the ovarian steroidogenesis is beneficial for understanding the impact of lipid nutrition on steroidogenesis. Herein, we identified that butyrate improved estradiol and progesterone synthesis in rat primary ovarian granulosa cells and human granulosa KGN cells and discovered the related mechanism. Our data indicated that butyrate was sensed by GPR41 and GPR43 in ovarian granulosa cells. Butyrate primarily upregulated the acetylation of histone H3K9 (H3K9ac). Chromatin immune‐precipitation and sequencing (ChIP‐seq) data of H3K9ac revealed the influenced pathways involving in the mitochondrial function (including cellular metabolism and steroidogenesis) and cellular antioxidant capacity. Additionally, increasing H3K9ac by butyrate further stimulated the PPARγ/CD36/StAR pathways to increase ovarian steroidogenesis and activated PGC1α to enhance mitochondrial dynamics and alleviate oxidative damage. The improvement in antioxidant capacity and mitochondrial dynamics by butyrate enhanced ovarian steroidogenesis. Collectively, butyrate triggers histone H3K9ac to activate steroidogenesis through PPARγ and PGC1α pathways in ovarian granulosa cells.