Effect Of Endosymbionts Wolbachia And Spiroplasma On Temperature Adaptability Of Tetranychus Truncatus

Arthropod symbiotic bacteria play an essential role in many aspects of host reproduction,immunity,metabolism,and resistance to environmental stress.Tetranychus truncatus Ehara is one of the most important polyphagous agricultural mite.The outbreak of T.truncatus in China has been a serious threat to crop production safety recently.Previous studies have shown that T.truncatus is commonly infected with a variety of symbiotic bacteria,but the role of these symbiotic bacteria in the temperature adaptability of T.truncatus and molecular mechanism involved are still unclear.In this study,we used genetics,biology,transcriptomics,and gene function analysis.Firstly,we investigated the survival rate and CI intensity of T.truncatus in different symbiotic infection modes under different temperature environments.Secondly,we also compared the dynamics of symbiotic bacteria in host under different temperatures.Finally,the transcriptional response patterns of host infected by different symbiotic bacteria to different temperatures were determined.The main results are as follows:1.Effects of different temperature on reproduction and CI phenotype of T.truncatus infected with different symbionts2.Four spider mite strains with a similar genetic background were established:strains co-infected with Wolbachia and Spiroplasma(designated as w+s+),Wolbachia only(w+),Spiroplasma only(s+)or no symbionts(w-s-).When the four mite strains were reared at and 35℃,the female survival rate after 5 days was sharply lower in the singly infected strains than in the co-infected and uninfected strains,which indicates that spider mites singly infected with Wolbachia or Spiroplasma are sensitive to high temperature.Spider mites infected with Spiroplasma may have a higher fitness at the intermediate temperature.High temperature and low temperature enhanced CI intensity in host population to different degrees.2.Effects of different temperatures on the transmission efficiency and titer of the symbionts in T.truncatus.High temperature not only affected the titer of symbiotic bacteria in the host,but also reduced the vertical transmission efficiency of symbiotic bacteria in the host population.Wolbachia titers in Wolbachia singly infected strains at 35℃decreased gradually over time and losted for three generations,which was different from the situation at 20℃.The co-infected strain showed sensitivity to both high temperature and low temperature,which Wolbachia titers increased over time and Spiroplasma titers fluctuated.Notably,Spiroplasma was lost in both co-infected and singly infected strains when mites were reared at 35°C for one generation.3.Preference temperature of T.truncatus infected with different symbiontsTemperature gradients were used to test the temperature preferences of four strains.The results showed that the preference of different strains to temperature was significantly different.The preferred average temperature of Wolbachia and Spiroplasma co-infected strains(T_p=20.74±0.22℃)and Wolbachia-infected strains(T_p=20.21±0.20℃)were significantly lower than either Spiroplasma-infected(T_p=22.31±0.20℃)or uninfected strains(T_p=22.47±0.18℃),representing a difference of around 2℃.These results indicated that spider mites infected with Wolbachia preferred cooler temperatures than uninfected spider mites.4.Transcriptional responses of T.truncatus infected with different symbionts to temperature stressThere were differences in the number of heat shock protein genes and transcriptional responses among the four strains under short time of high and low-temperature stress.For the low temperature(20℃)comparison,Spiroplasma-infected strains showed the most differently expressed genes(DEGs).For 35℃comparison,the number of DEGs in un-infected strains was higher than that in the other three spider mite strains when compared to the control treatments.The co-infected strain had the fewest DEGs compared with the other three mite strains under both high and low-temperature exposure.Among the DEGs,expression of the heat shock protein genes,including Hsp20,Hsp70 and Hsp90,varied in particular between the four spider mite strains.In conclusion,the endosymbiont-mediated response to temperature stress is complex,which is the result of the interaction of endosymbiont-mediated infection mode,temperature regulation behavior and transcription factors.Under the background of global climate warming,the results of this study can help to analyze the mechanism of pest outbreaks and provide theoretical guidance for the green prevention and control.