Background
A new Bacillus thuringiensis X023 (BtX023) with high insecticidal activity was isolated in Hunan Province, China. The addition of metals (Cu, Fe, Mg and Mn) to the medium could influence the formation of spores and/or insecticidal crystal proteins (ICPs). In previous studies, Cu ions considerably increased the synthesis of ICPs by enhancing the synthesis of poly-β-hydroxy butyrate. However, the present study could provide new insights into the function of Cu ions in ICPs.
Results
Bioassay results showed that wild strain BtX023 exhibited high insecticidal activity against Plutella xylostella. The addition of 1 × 10−5 M Cu2+ could considerably increase the expression of cry1Ac and vip3Aa, and the insecticidal activity was enhanced. Quantitative real-time polymerase chain reaction (qRT-PCR) and proteomic analyses revealed that the upregulated proteins included amino acid synthesis, the glyoxylate pathway, oxidative phosphorylation, and poly-β-hydroxy butyrate synthesis. The Cu ions enhanced energy metabolism and primary amino acid synthesis, will providing abundant raw material accumulation for ICP synthesis.
Conclusion
The new strain BtX023 exerted a strong insecticidal effect on P. xylostella by producing ICPs. The addition of 1 × 10−5 M Cu2+ in the medium could considerably enhance the expression of the cry1Ac and vip3Aa genes, thereby further increasing the toxicity of BtX023 to Helicoverpa armigera and P. xylostella by enhancing energy synthesis, the glyoxylate cycle, and branched-chain amino acids synthesis, but not poly-β-hydroxy butyrate synthesis.
Using data from China Annual Survey of Industrial Firms and addressing potential endogeneity problem, we find that corporate tax burden in China is procyclical during recessions and countercyclical during booms. The cyclicality is stronger for enterprises whose corporate income taxes are levied by Local Tax Bureau (LTB). Procyclicality of corporate tax burden during recessions is larger for enterprises located in county, non‐state‐owned enterprises (non‐SOEs), non‐high‐tech enterprises and large‐medium enterprises. Furthermore, tax quotas and growth targets of local governments enhance procyclicality during recessions and the countercyclicality of corporate tax burden during booms. Tax collection and government spending are important channels through which tax quotas and growth targets affect the cyclicality of corporate tax burden, respectively. This paper provides important policy implications for China during economic recessions.
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