Multilayered synergistic regulation of phytoalexin biosynthesis by ethylene, jasmonate, and MAPK signaling pathways in Arabidopsis.

Camalexin, an indolic antimicrobial metabolite, is the major phytoalexin in Arabidopsis thaliana, and plays a crucial role in pathogen resistance. Our previous studies revealed that the Arabidopsis mitogen-activated protein kinases MPK3 and MPK6 positively regulate pathogen-induced camalexin biosynthesis via phosphoactivating the transcription factor WRKY33. Here, we report that the ethylene and jasmonate (JA) pathways act synergistically with the MPK3/MPK6-WRKY33 module at multiple levels to induce camalexin biosynthesis in Arabidopsis upon pathogen infection. The ETHYLENE RESPONSE FACTOR1 (ERF1) transcription factor integrates the ethylene and JA pathways to induce camalexin biosynthesis via directly upregulating camalexin biosynthetic genes. ERF1 also interacts with and depends on WRKY33 to upregulate camalexin biosynthetic genes, indicating that ERF1 and WRKY33 form transcriptional complexes to cooperatively activate camalexin biosynthetic genes, thereby mediating the synergy of ethylene/JA and MPK3/MPK6 signaling pathways to induce camalexin biosynthesis. Moreover, as an integrator of the ethylene and JA pathways, ERF1 also acts as a substrate of MPK3/MPK6, which phosphorylate ERF1 to increase its transactivation activity and therefore further cooperate with the ethylene/JA pathways to induce camalexin biosynthesis. Taken together, our data reveal the multilayered synergistic regulation of camalexin biosynthesis by ethylene, JA, and MPK3/MPK6 signaling pathways via ERF1 and WRKY33 transcription factors in Arabidopsis.

Effect of Bacillus thuringiensis biomass and insecticidal activity by cultivation with vegetable wastes.

Bacillus thuringiensis (Bt) has been regarded as a biopesticide with high efficiency and safety, while it still cannot be popularized and mass-produced because of its high production costs. In the present study, we aimed to develop a cost-effective biopesticide via the secondary use of discharged vegetable wastes as the raw fermentation medium, and the insecticidal activity of Bt strain prepared by this cheap cultivation approach was evaluated. The suitable carbon source, nitrogen source additives and optimal metal ions were screened by the single-factor test, and the optimal combination of additives was determined by orthogonal test and ANOVA analysis. We found that soluble starch (6 g l-1), soya bean meal (6 g l-1), Al3+ (0.4 g l-1) and Fe2+ (0.4 g l-1) were the optimal exogenous additives, and the optimal fermentation conditions were as follows: pH 7.0, temperature of 35°C and aeration of 80 ml/250 ml. Meanwhile, the bioactivity test results showed that the Bt strain prepared by cheap cultivation still exhibited a good insecticidal effect on Helicoverpa armigera compared with the standard LB medium. Collectively, our findings provided a new strategy for vegetable waste utilization with less environmental impact and reduced production cost.

Flowerlike Mg(OH)2 Cross-Nanosheets for Controlling Cry1Ac Protein Loss: Evaluation of Insecticidal Activity and Biosecurity.

Bacillus thuringiensis (Bt) can produce Cry proteins during the sporulation phase, and Cry protein is effective against lepidopteran, coleopteran, and dipteran insects and nematodes. However, Cry protein tends to be discharged into soil and nontarget plants through rainwater runoff, leading to reduced effective period toward target insects. In the present study, nano-Mg(OH)2 (magnesium hydroxide nanoparticles, MHNPs) were synthesized to control the loss of Cry1Ac protein and deliver protein to Helicoverpa armigera (Lepidoptera: Noctuidae). The results showed that Cry1Ac protein could be loaded onto MHNPs through electrostatic adsorption, and both MHNPs and Cry protein were stable during the adsorption process. Meanwhile, the Cry1Ac-loaded MHNPs could remain on the surface of cotton leaves, resulting in enhanced adhesion of Cry1Ac protein by 59.50% and increased pest mortality by 75.00%. Additionally, MHNPs could be slowly decomposed by acid medium and MHNPs showed no obvious influence on cotton, Bt, Escherichia coli, and H. armigera. Therefore, MHNPs could serve as an efficient nanocarrier for delivery of Cry1Ac protein and be used as a potential adjuvant for biopesticide in agricultural applications.

Adsorption of Insecticidal Crystal Protein Cry11Aa onto Nano-Mg(OH)2: Effects on Bioactivity and Anti-Ultraviolet Ability.

The traditional Bacillus thuringiensis (Bt) formulations for field applications are not resistant to harsh environmental conditions. Hence, the active ingredients of the Bt bioinsecticides could degrade quickly and has low anti-ultraviolet ability in the field, which significantly limits its practical application. In the present study, we developed an efficient and stable delivery system for Bt Cry11Aa toxins. We coated Cry11Aa proteins with Mg(OH)2 nanoparticles (MHNPs), and then assessed the effects of MHNPs on bioactivity and anti-ultraviolet ability of the Cry11Aa proteins. Our results indicated that MHNPs, like "coating clothes", could effectively protect the Cry protein and enhance the insecticidal bioactivity after UV radiation (the degradation rate was decreased from 64.29% to 16.67%). In addtion, MHNPs could improve the proteolysis of Cry11Aa in the midgut and aggravate the damage of the Cry protein to the gut epithelial cells, leading to increased insecticidal activity against Culex quinquefasciatus. Our results revealed that MHNPs, as an excellent nanocarrier, could substantially improve the insecticidal bioactivity and anti-ultraviolet ability of Cry11Aa.

The adsorption features between insecticidal crystal protein and nano-Mg(OH)2.

Nano-Mg(OH)2, with low biological toxicity, is an ideal nano-carrier for insecticidal protein to improve the bioactivity. In this work, the adsorption features of insecticidal protein by nano-Mg(OH)2 have been studied. The adsorption capacity could reach as high as 136 mg g-1, and the adsorption isotherm had been fitted with Langmuir and Freundlich models. Moreover, the adsorption kinetics followed a pseudo-first or -second order rate model, and the adsorption was spontaneous and an exothermic process. However, high temperatures are not suitable for adsorption, which implies that the temperature would be a critical factor during the adsorption process. In addition, FT-IR confirmed that the protein was adsorbed on the nano-Mg(OH)2, zeta potential analysis suggested that insecticidal protein was loaded onto the nano-Mg(OH)2 not by electrostatic adsorption but maybe by intermolecular forces, and circular dichroism spectroscopy of Cry11Aa protein before and after loading with nano-Mg(OH)2 was changed. The study applied the adsorption information between Cry11Aa and nano-Mg(OH)2, which would be useful in the practical application of nano-Mg(OH)2 as a nano-carrier.