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[Objectives] To determine the biological safety of BT protein from Bacillus thuringiensis (Bt) fermentation broth to mammals at high doses. [Methods] Healthy mice were randomly divided into 4 groups with 10 mice in each group. The experimental groups were fed with Bt fermentation supernatant at 0.2, 0.6 and 1.0 mL/kg, respectively, once a day for 7 consecutive days. The blank control group was fed normally without intragastric administration. [Results] There was no significant difference in blood routine and blood biochemical analysis between the experimental group and the control group. After intragastric administration, the mice were dissected, and no obvious pathological changes were found; the heart, liver, spleen, lung and kidney were taken to make tissue sections, and no pathological changes were found by microscopic observation. [Conclusions] Mice can tolerate high doses of BT protein from B. thuringiensis fermentation broth. [ABSTRACT FROM AUTHOR]

• Bt protein levels in transgenic rice vary significantly across different growth stages and organs. • Bt protein levels higher in cry2A* than cry1C* transgenic early japonica rice. • Bt protein levels are highest in leaves, followed by stem sheaths and young panicles. • Expression levels of Bt proteins in brown rice are the lowest among all growth stages and organs. • Correlation between Bt gene transcription and protein levels is significant in various rice tissues. Transgenic insect-resistant rice offers an environmentally friendly approach to mitigate yield losses caused by lepidopteran pests, such as stem borers. Bt (Bacillus thuringiensis) genes encode insecticidal proteins and are widely used to confer insect resistance to genetically modified crops. This study investigated the integration, inheritance, and expression characteristics of codon-optimised synthetic Bt genes, cry1C* and cry2A*, in transgenic early japonica rice lines. The early japonica rice cultivar, Songgeng 9 (Oryza sativa), was transformed with cry1C* or cry2A*, which are driven by the ubi promoter via Agrobacterium tumefaciens-mediated transformation. Molecular analyses, including quantitative PCR (qPCR), enzyme-linked immunosorbent assay (ELISA), and Southern blot analysis were performed to confirm transgene integration, inheritance, transcriptional levels, and protein expression patterns across different tissues and developmental stages. Stable transgenic early japonica lines exhibiting single-copy transgene integration were established. Transcriptional analysis revealed variations in Bt gene expression among lines, tissues, and growth stages, with higher expression levels observed in leaves than in other organs. Notably, cry2A* exhibited consistently higher mRNA and protein levels than cry1C* across all examined tissues and developmental time points. Bt protein accumulation followed the trend of leaves > stem sheaths > young panicles > brown rice, with peak expression during the filling stage in the vegetative tissues. Synthetic cry2A* displayed markedly elevated transcription and translation compared to cry1C* in the transgenic early japonica rice lines examined. Distinct spatiotemporal patterns of Bt gene expression were elucidated, providing insights into the potential insect resistance conferred by these genes in rice. These findings will contribute to the development of insect-resistant japonica rice varieties and facilitate the rational deployment of Bt crops. [ABSTRACT FROM AUTHOR]