| Bemisia tabaci Mediterranean(MED)cryptic species had been rapidly spread to all provinces since it invaded into China,and gradually replaced Middle East-Asia Minor 1(MEAM1)or indigenous whiteflies in many regions.However,the native species Asia Ⅱ 1 was only distributed in several southern regions of the country.One of the most important reasons for the successful invasion and rapid occupation of habitats in different areas of MED cryptic species was its rapid adaptability to different temperature conditions.Epigenetic modification is an important way for B.tabaci MED to rapidly deal with the thermal stress.To investigate the roles of chromatin remodeling factors in thermal adaptation of whiteflies,we firstly cloned the iswi,brm1 and brm2 genes from both Asia Ⅱ 1 and MED,then the expression patterns of these three genes under short-term temperature stress in the two cryptic species were compared.Then the heat tolerance and cold tolerance were detected after RNAi.Finally,the temperature preference behavior of Asia Ⅱ 1 and MED adults after dsRNA feeding were examined.The main results and conclusions are discussed below.1.Cloning and sequence analysis of chromatin remodeling factors in B.tabaciIn this study,the full-length c DNA of iswi,brm1 and brm2 genes were cloned from Asia Ⅱ 1 and MED,and were named Asia Ⅱ 1-Btiswi,MED-Btiswi,Asia Ⅱ 1-Btbrm1,MED-Btbrm1,Asia Ⅱ1-Btbrm2 and MED-Btbrm2,respectively.Asia Ⅱ 1-Btiswi and MED-Btiswi shared 99.71% similarity,and there were three variable sites.Asia Ⅱ 1-Btbrm1 and MED-Btbrm1 shared 99.85% similarity,with six amino acid variable sites.And the deduced amino acid sequence similarity between Asia Ⅱ 1-Btbrm2 and MED-Btbrm2 was 99.41%,with nine variable sites.We hypothesized that the presence of these mutation sites,especially some key mutation sites,might be one of the reasons for the difference in temperature tolerance between the two species.2.Expression profiles of chromatin remodeling factors under temperature stressCompared with individuals maintained at 26℃(the control temperature),MED-Btiswi and AsiaⅡ1-Btiswi mRNA expression levels were up-regulated after exposure to heat shock or cold shock conditions,and the expression of MED-Btiswi under high temperature stress was significantly higher than that of Asia Ⅱ 1-Btiswi.Under cold shock conditions,the expression of Btbrm1 gene in the two cryptic species were down-regulated.Interestingly,under heat shock conditions,the expression pattern of MED-Btbrm1 and Asia Ⅱ 1-Btbrm1 were opposite(MED was up-regulated,but Asia Ⅱ 1 was down-regulated).In addition,the expression of MED-Btbrm2 was significantly up-regulated after exposure to thermal stress,while Asia Ⅱ 1-Btbrm2 was significantly down-regulated.These data indicated that temperature stress could induce the expression of Btiswi,Btbrm1,and Btbrm2 in whiteflies.We hypothesized that the difference in expression patterns of these three genes between AsiaⅡ 1 and MED might be related to phenotypic plasticity and adaptability in response to environmental stresses.3.The functions of chromatin remodeling factors in thermal stress of B.tabaciHeat resistance or cold resistance of both MED and Asia Ⅱ 1 were significantly reduced after the knock-down of Btiswi or Btbrm2.However,after feeding with dsbrm1,only the heat resistance was significantly decreased,and there was no significant difference in cold resistance.We hypothesized that iswi,brm1 and brm2 in B.tabaci were involved in the regulation of their body’s responses to temperature stress,and affected their thermal tolerance.4.Influence of Btiswi on B.tabaci’s preferred temperatureWe used a linear thermal gradient to assess whether the temperature preference behavior of whitefly adults changed after dsRNA feeding.Results showed that the preferred temperatures of treatment groups from both Asia Ⅱ 1 and MED were increased.These findings indicated that the iswi gene might be involved in the temperature sensing of whiteflies and affected their temperature preference behavior. |
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