Functional Analysis Of Takeout Protein In The Phase Transition Of Locusta Migratoria

The migratory locust, Locusta migratoria, is a widespread pest that is distributed in Europe, Asia, Africa, and Australia. They also have a broad distribution in China. In L. migratoria, there are two phases, solitarious and gregarious phases, which can transform into the other. Locust outbreaks are mainly caused by the transform of the solitarious into the gregarious phase and the formation of swarm bands.Takeout family is a big insect-specific protein family formed during long evolution. They are secretary proteins containing about 250 amino acids. Takeout proteins are abundantly distributed in several tissues related to chemical sense and nutrition, for example, antennae, tarsi, fat body and cardia. So far, they are revealed to be involved in circadian rhythm, feeding and locomotor activity, chemical sensation, sex-determination, and male courtship behavior. Many scholars thought that takeout proteins could bind different hydrophobic ligands which could perform different functions, but there were no direct evidence.Recent research revealed that, during solitarization and gregarization of L. migratoria, the expression of 453 genes differed significantly, including many takeout genes. Among these takeout genes, LimgTO1 is proposed to accept singals from other individuals causing phase change, but the relationship between other takeout genes and phase change remains unclear.We analyzed the third-day fourth instar nymphs using LimgTO2, which is one of the above takeout gene families. The signal peptide prediction revealed that LimgTO2 possesses signal peptide sequence. Phylogenetic analyses supported that LimgTO2 belongs to the takeout family. The two Cys residues in the N terminus indicated that LimgTO2 could bind ligands. The tissue-specific expression and differential expression profiling of the LimgTO2 gene during phase transition of L. migratoria were analyzed by real-time quantity PCR and Western blot. The gene had a significantly higher expression level in solitarious locusts than gregarious locusts, with the most different expression in the tissue of hind legs. The expression of LimgTO2 was down-regulated during the gregarizaiton process and up-regualted during the reverse process. The above results indicate that the LimgTO2 gene is involved in the regulation of locust phase transition. The results of real-time quantity PCR, Western blot and immunohistochemistry methods reveal that the LimgTO2 protein is distributed in epidermis of locust hind legs. The conclusion is that the sensory hair in hind legs of solitarious locusts can sense external stimuli and transmit the signals via some hormones or signal proteins, and that the LimgTO2 gene acts as a carrying protein involved in the phase transition of L. migratoria.Although there have been many strudies about the mechanism of the phase transition of the L. migratoria, the present research represents the effort at the molecular level. Moreover, current methods of locust control are mainly focusd on chemical drugs which may cause environmental and ecological pollution. The present study provides solid genetic evidence for the phase transition of L. migratoria, which may help improve the design of biological pest-control measures.