Comparison Of The Abilities And Molecular Mechanisms Underlying Tobacco Curly Shoot Virus Transmission By Different Bemisia Tabaci Cryptic Species

Bemisia tabaci is a complex of 36 cryptic species.During the last 20 years,Middle East Asia Minor 1(MEAM1) and Mediterrannean(MED),two invasive cryptic species rapidly occupied many provinces and regions in our country because of their extensive host adaptability,strong insecticide resistance and high reproductive rate and greatly threatens our agricultural production.Bemisia tabaci can effectively transmit begomoviruses in a persistent manner.Tobacco curly shoot virus(TbCSV),a begomovirus found on the tobacco in Yunnan,China in 2001,broke out in northeastern India in 2015 and caused serious tomato disease.In order to clarify the different transmission abilities of TbCSV by different B.tabaci cryptic species,we used four cryptic species MEAM1,MED,Asia 1 and Asia ? 1 for our experiments.Furthermore,we investigated the molecular mechanisms underlying the differences of TbCSV transmission between MEAM1 and Asia ? 1.The results were summarized as follows:(1)Comparison of TbCSV transmission abilities by MEAM1,MED,Asia 1 and Asia ? 1.Among these four cryptic species,we found that Asia ? 1 transmitted TbCSV at the highest efficiency,whereas MEAM1 transmitted it at the lowest efficiency.Using one female for transmission test,the transmission efficiency of Asia ? 1 was 44.4% and MEAM1 couldn't transmit TbCSV successfully.Using 5 females for transmission test,the transmission efficiency of TbCSV by Asia ? 1 was 96.3%;and MEAM1 still couldn't transmit TbCSV successfully.The relative quantity of TbCSV in whiteflies increased over time and the TbCSV acquisition ability by Asia ? 1 was also significantly higher than that by MEAM1.However,the relative quantity of virus in the honeydew of MEAM1 was significantly higher than that of Asia ? 1.Therefore,we suggested that both MEAM1 and Asia ? 1 can gain virions from plants efficiently,but TbCSV couldn't finish the circulative journey in MEAM1 whiteflies,maybe due to some potential physiological barriers.(2)Mechanisms underlying the differences of TbCSV transmission between MEAM1 and Asia ? 1.With the help of q PCR analysis,we found that the relative viral quantities in the midgut,haemolymph and primary salivary glands of Asia ? 1 were significantly higher than that of MEAM1.After acquiring TbCSV for 12 h,the virus signals could be found in midgut of Asia ? 1;and these signals became stronger over time.After 24 h viral access acquisition period,the viral signals in primary salivary glands of Asia ?1 could be visualized.Next,we purified the TbCSV virions from infected plants and microinjected TbCSV virions into whitelfy haemolymph to help TbCSV across midgut barrier.We found that the viral transmission efficiency of MEAM1 became higher,though Asia ? 1 still transmitted TbCSV more effectively than MEAM1.These results indicate that midgut plays an important role in the process of TbCSV intracellular journey in whitefly and the primary salivary gland may also constrain TbCSV transmission in MEAM1.To investigate the role of TbCSV CP(coat protein)in its transmission,we exchanged the CP region of TYLCV with that of TbCSV.After CP exchange,TYLCV signals could be found in the midgut and primary salivary glands of MEAM1,but mTYLCV signals couldn't be detected.In summary,we examined the different transmission abilities of TbCSV by four B.tabaci cryptic species.To a large extent,the midgut of Asia ? 1 determined its higher efficiency in TbCSV transmission.In addition,we provided a new evidence for the importance of begomovirus CP in its transmission.