Study On Molecular Mechanism Of Co-infection Of Wolbachia And Spiroplasma Regulating The Reproduction And Fitness Of Tetranychus Truncatus

Tetranychus truncatus is an important pest in China.It has been regarded as one of the most notorious pests as its wide host range,small size,strong fertility,short development time,strong adaptability and drug resistance.T.truncatus have a serious outbreak and become the dominant pest in China in recent years.Wolbachia and Spiroplasma are intracellular bacteria which infect a large number of arthropods.A huge number of evidence showed that symbionts could facilitate their spread in host population by influencing host reproduction or fitness.Research has shown that co-infection is frequent in natural,but the research about co-infection of Wolbachia and Spiroplasma in T.truncatus is deficient,it is necessary to study the reproduction and fitness effects conferred by symbont infection and their potential mechanisms.In this study,we established four different symbiont-infected mite lines with consistent genetic backgrounds by tetracycline treatment and genetic crossing,which contained doubly infected(Iws),singly Wolbachia-infected(Iw),singly Spiroplasma-infected(Is)and uninfected(U)lines.And we studied the interaction between endosymbionts and hosts,including the reproduction and fitness effects conferred by symbiont infection,competitive relationship between Wolbachia and Spiroplasma,and compared gene expression profiles among four different symbiont-infected male lines.The main results are listed as follow.1.The reproduction and fitness effects of co-infection of Wolbachia and SpiroplasmaWe investigated the reproduction and fitness effects conferred by symbiont infection.Results shown that 1)co-infection suppressed mite oviposition.2)Symbiont infection could increase hatch proportion of males,and doubly infected line increased most.3)Co-infection could shorten development time of hosts.4)Singly infection of either Wolbachia or Spiroplasma could increase longevity of male mites.5)For doubly infected line,longevity of female which crossed with the same symbiont infection male or uninfected male was longer than with singly Spiroplasma-infected male.For singly Spiroplasma-infected line,longevity of femalewhich crossed with the same symbiont infection male or uninfected male was longer than with doubly infected male.2.Competitive relationship between Wolbachia and Spiroplasma in T.truncatusWe investigated the competitive relationship between Wolbachia and Spiroplasma.Results shown that 1)Symbiont titer had no significant effect when the density of mites on identical plant changed.2)Crossing type of mites had an effect on symbiont titer,the existence of Spiroplasma hardly influenced Wolbachia titer,the existence of Wolbachia greatly reduced Spiroplasma titer,and Wolbachia occupied dominant position in the competitive relationship with Spiroplasma.3.Co-infection of Wolbachia and Spiroplasma changed the gene expression of T.truncatusWe compared gene expression profiles among four males from different symbiont-infected lines.We found that co-infection changed the expression of many genes compared with other lines,including genes related to digestion detoxification,lipocalins,oxidation reduction,reproduction and immunity.In conclusion,our study comfirmed the reproduction and fitness effect of Wolbachia and Spiroplasma infection on T.truncatus,and Wolbachia occupied dominant position relative to Spiroplasma.Especially,investigated effect of co-infection on male mites using RNA-Seq.Our results helps elucidate the complex interactions between endosymbionts and arthropods.