Genome-wide identification and characterization of HSP gene superfamily in whitefly (Bemisia tabacl)and expression profiling analysis under temperature stress

Heat shock proteins (HSP)are essential molecular chaperones that play important roles in the stress stimulation of insects.Bemisia tabaci,a phloem feeder and invasive species,can cause extensive crop damage through direct feeding and transmission of plant viruses.Here we employed comprehensive genomics approaches to identity HSP superfamily members in the Middle East Asia Minor 1 whitefly genome.In total,we identified 26 Hsp genes,including three Hsp90,17 Hsp70,one Hsp60 and five sHSP (small heat shock protein)genes.The HSP gene superfamily of whitefly is expanded compared with the other five insects surveyed here.The gene structures among the same families are relatively conserved.Meanwhile,the motif compositions and secondary structures of BtHsp proteins were predicted.In addition,quantitative polymerase chain reaction analysis showed that the expression patterns of BtHsp gene superfamily were diverse across different tissues of whiteflies.Most Hsp genes were induced or repressed by thermal stress (40℃)and cold treatment (4℃)in whitefly.Silencing the expression of BtHsp70-6 significantly decreased the survival rate of whitefly under 45℃.All the results showed the Hsps conferred thermo-tolerance or cold-tolerance to whiteflies that protect them from being affected by detrimental temperature conditions.Our observations highlighted the molecular evolutionary properties and the response mechanism to temperature assaults of Hsp genes in whitefly.

Genomic and transcriptomic analyses reveal metabolic complementarity between whiteflies and their symbionts

Nutritional mutualism between insects and symbiotic bacteria is widespread.The various sap-feeding whitefly species within the Bemisia tabaci complex associate with the same obligate symbiont(Portiera)and multiple secondary symbionts.It is often assumed that some of the symbionts residing in the whiteflies play crucial roles in the nutritional physiology of their insect hosts.Although effort has been made to understand the functions of the whitefly symbionts,the metabolic complementarity offered by these symbionts to the hosts is not yet well understood.We examined two secondary symbionts,Arsenophonus and Wolbachia,in two species of the B.tabaci whitefly complex,provisionally named as Asia II 3 and China 1.Genomic sequence analyses revealed that Arsenophonus and Wolbachia retained genes responsible for the biosynthesis of B vitamins.We then conducted transcriptomic surveys of the bacteriomes in these two species of whiteflies together with that in another species named MED of this whitefly complex previously reported.The analyses indicated that several key genes in B vitamin syntheses from the three whitefly species were identical.Our findings suggest that,similar to another secondary symbiont Hamiltonella,Arsenophonus and Wolbachia function in the nutrient provision of host whiteflies.Although phylogenetically distant species of symbionts are associated with their respective hosts,they have evolved and retained similar functions in biosynthesis of some B vitamins.Such metabolic complementarity between whiteflies and symbionts represents an important feature of their coevolution.