| Liriomyza trofilii belongs to Diptera,Agromyzidae,and Phytomyzidae.It mainly occurs on Leguminosae,Solanaceae,Cucurbitaceae and other vegetables.It is an important alien invasive pest in China,and also one of the main leafminer in Jiangsu Province.Rapid cold hardening is a phenomenon that can significantly improve the cold tolerance of insects after a short period of mild and low-temperature acclimation.Study on rapid cold hardening is of great significance to the prediction of overwintering situation of agricultural pests,the integrated control of greenhouse,storage,and some quarantine pests,and the cryopreservation of experimental insects and beneficial insects.In this study,the phenomenon of rapid cold hardening in L.trifolii was studied,and the mechanism of it was discussed from the physiological,biochemical and molecular levels,to provide the basis for the study of low-temperature adaptability of insects.The main results are as follows.1.The results showed that rapid cold hardening exists in both adults and pupae of L.trifolii.Maximum survival was recorded in 7-day-old pupae after acclimation at 1℃ for 4hr,prior exposure to discriminating temperature,resulting in enhanced survival from 20%to more than 80%.In addition,the protection gained through the RCH phenomena were decreased after recovery time,which suggests that this protection is not permeant and can be lost or faded after the recovery time.After 4 hours of recovery at 26℃,there was no significant difference between the survival of the acclimated and the control.2.Based on the study of the rapid cold hardening phenomenon of L.trifolii,the physiological and biochemical mechanism was studied.The results showed that the supercooling point of 2-day-old pupae decreased from-18.8℃ to-20.1℃ after 4 hours of acclimation.Similarly,the supercooling points of 5-day-old and 7-day-old pupae decreased by about 1℃,The supercooling point of adults decreased by 1.7℃;At room temperature,the unsaturation of fatty acids of L.trifolii adults were 0.95,while after four hours of low temperature acclimation,the content of unsaturated fatty acids increased and the content of saturated fatty acids decreased,which led to the unsaturation of fatty acids increased to 1.1;The contents of sugar alcohols changed significantly.Among them,the changing trend of glucose and trehalose was similar,and they both accumulated significantly after four hours of acclimation.The contents of glucose and trehalose in the former were significantly higher than those in the latter by comparing the acclimated adults under low-temperature stress with those under direct low-temperature stress.These results indicate that the changes in fatty acid composition,accumulation of antifreeze substances and other physiological and biochemical levels are important mechanisms of rapid cold hardeing in L.trifolii.3.Based on the transcriptome analysis of rapid cold tolerance of L.trifolii,493 genes were differentially expressed after 4 hours of acclimation;There were also 385 differentially expressed genes between cold shock and cold shock following acclimation.Among them,the genes with the highest expression included fat body,cortical protein and DNA binding protein.KEGG pathway enrichment analysis showed that these differentially expressed mRNA were clustered in multiple metabolic pathways,including energy metabolism pathway(metabolism of various amino acids and sugars),fatty acid metabolism pathway and MAPK signaling pathway,which indicated that transcriptional regulation was one of the important molecular mechanisms of rapid cold hardening in L.trifolii. |
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