Erwinia amylovora is a plant pathogen that causes fire blight disease in Rosaceous plants, such as pear and apple. To develop an effective biocontrol method to suppress E. amylovora, a total of 16 bacteria were isolated from pear orchard soil in China and screened for antagonistic activity in vitro. Among them, 9 isolates that exhibited antagonistic activity against E. amylovora were identified, including Bacillus atrophaeus, Priestia megaterium (previously known as Bacillus megaterium) and Serratia marcescens based on the partial 16S rDNA sequence analysis and similarity search. The plate confrontation experiments showed that strain 8 (P. megaterium strain KD7) had strong antagonistic activity against E. amylovora. The methanolic extract from cell-free supernatant of strain KD7 displayed high antibacterial activities against E. amylovora. Furthermore, the active compounds of strain KD7 were separated by thin layer chromatography (TLC) and the amino acids were detected by the presence of a spot with retention factor (Rf) of 0.71. Next, three lipopeptides were identified with high-resolution mass spectrometry (HRMS), including C13-surfactin [M+H]+ at m/z 1008.14, C15-surfactin [M+H]+ at m/z 1036.50, and C14-iturin A [M+H]+ at m/z 1043.17. Strain KD7 showed multiple antibiotic resistance, such as ampicillin, erythromycin, penicillin and tetracycline. The detached pear leaves, twigs and fruits assay showed that both protective and curative action with strain KD7 had the ability to decrease the development of fire blight. Taken together, P. megaterium strain KD7 is a potential effective biocontrol agent against fire blight.
The wax esters are important cuticular wax composition that cover the outer surface of plant organs and play a critical role in protection and energy metabolism. Wax ester synthesis in plant is catalyzed by a bifunctional wax ester synthase/acyl-CoA: diacylglycerol acyltransferase (WSD). Sunflower (Helianthus annuus L.) is an important oil crop in the world; however, little is known about WSD in sunflower. In this study, we identified and performed a functional analysis of twelve HaWSD genes from sunflower genome. Tissue-specific expression revealed that 12 HaWSD genes were differentially expressed in various organs and tissues of sunflower, except seeds. HaWSD genes were highly induced by salinity, drought, cold, and abscisic acid (ABA) in sunflower. To ascertain their function, HaWSD9, with highly expressed levels in stems and leaves, was cloned and expressed in a yeast mutant defective in triacylglycerol (TAG) biosynthesis. HaWSD9 complemented the phenotype by producing wax ester but not TAG in vivo, indicating that it functions as a wax ester synthase. Subcellular localization analysis indicated that HaWSD9 was located in the endoplasmic reticulum (ER). Heterologous introduction of HaWSD9 into Arabidopsis wsd1 mutant exhibited increased epicuticular wax crystals and cuticular wax contents on the stems. As compared with the wsd1 mutant, HaWSD9 overexpressing transgenic Arabidopsis showed less cuticle permeability, chlorophyll leaching and water loss rate. Further analysis showed that the HaWSD9 transgenics enhanced tolerance to ABA, mannitol, drought and salinity, and maintained higher leaf relative water content (RWC) than the wsd1 mutant under drought stress, suggesting that HaWSD9 play an important physiological role in stress response as well as wax synthase. These results contribute to understanding the function of HaWSD genes in wax ester synthesis and stress tolerance in sunflower.
Higher pressure die casting (HPDC) AM series (Mg-Al-Mn) Mg alloys have wide application potential in the automobile industry. To promote its application, systematic investigation on the corrosion performance and corrosion residual strength of HPDC AM50+1Ce and AM60 was carried out. The corrosion of HPDC AM50+1Ce was more uniform, while the pitting corrosion of AM60 was more severe, and the mechanical properties of HPDC AM60 was more sensitive to corrosion. The residual strength of AM50+1Ce and AM60 after corrosion of 648 h was 199 MPa and 183 MPa, respectively. The findings can contribute to a better understanding of the corrosion and residual strength of HPDC AM series Mg alloys.
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