| The bird cherry-oat aphid,Rhopalosiphun padi(L.)(Hemiptera: Aphididae),is one of the most destructive wheat pest,with widely distribution around the world.The aphid shows a differentiation of life cycle and morphology polymorphism under different climatic condition.Vision is one of the most direct sources of external information.As the most important visual organ of insects,compound eye size and number of ommatidias within it,reflect the visual ability of insects.Opsins,the essential component of the light signal transduction pathway,act as a functional molecule of visual perception.The expression of opsin genes is influenced by a variety of endogenous and exogenous factors.In current study,we firstly observed and compared the external morphology of compound eye among five aphid forms and between two types of life cycle from R.padi using scanning electron microscopy(SEM).The results provide the basis for understanding the relationship between insect vision and living environment.Seven opsin genes were cloned,and the relative expression pattern of opsin genes at five aphid forms,in different developmengtal stages,in the adults with different life cycles,in different wing morphs was analyzed.Simulating the autumn climate condition,we explored the difference in the expression pattern of seven opsin genes between holocyclic and anholocyclic lineages of R.padi when respond to low temperature and short-day photoperiod.The results provide a basis for understanding the evolutionary relationship of opsins,and evidence for the role of opsin in response to changes in environment factors such as photoperiod among different life cycle in R.padi.1.The compound eye external morphology of R.padiThe compound eye of adult R.padi is oval and located in the base of the antennae of head,with no sensory hairs in the separation of ommatidias.There are significant differences in the size of compound eye,the number of ommatidias,and the diameter of ommatidium among the five ahpid froms of R.padi with holocylic life cycle.In combination with the parameters,it is assumed that the visual ability of five aphid forms from strong to weak is: male,winged virginoparae,gynoparae,wingless virginoparae and oviparae.There is no significant difference in the parameters of compound eyes between holocyclic and anholocyclic wingless virginoparae of R.padi.2.Cloning and sequence analyses of opsin genes from R.padiSeven opsin genes(Rp-lwo?Rp-uvo1?Rp-uvo2?Rp-uvo3?Rp-uvo4?Rp-rho?Rp-Co)were successfully cloned from R.padi.Amino acid sequence analysis showed that opsin genes contain seven transmembrane helix domian,G-protein coupled receptors familt signature;except for Rp-RHO and Rp-CO,all have retinal binding sites.Sequence similarity analysis showed that the amino acid sequence of seven opsin genes of R.padi were highly similar to those of the corresponding protein sequence of opsin genes of Acyrthosiphon pisum and Myzus persicae.Phylogenetic tree showed that Rp-LWO,Rp-UVO1,and Rp-UVO2 were clustered together with the visual sensitization functional opsin of other insects,and the other four opsins were grouped together with non-visual sensitization functional opsin of other insects.3.Relative expression of opsin genes in different aphid forms,different developmengtal stages,two life cycle,different wing morphs of R.padiThe relative expression levels of seven opsin genes(Rp-lwo?Rp-uvo1?Rp-uvo2?Rp-uvo3?Rp-uvo4?Rp-rho?Rp-Co)varied in different aphid forms,developmengtal stages,life cycle,and wing morphs.Among the five aphid forms of R.padi with holocyclic life cycle,the highest levels of transcription of all opsin genes were observed in males,and the lowest in oviparae.In different developmental stages of R.padi with holocyclic life cycle,the expression levels of Rp-lwo,Rp-uvo1,Rp-uvo2,and Rp-rho in the fourth instar were the lowest,while highest in first instar;both Rp-uvo3 and Rp-uvo4 had the lowest expression levels in the first instar and the highest expression level in the winged virginoparae;The highest expression level of Rp-Co occurred in the second instar.The expression patterns of Rp-lwo,Rp-uvo3,Rp-uvo4,and Rp-Co about different wing morph virginoparae were discrepant between holocyclic and anholocyclic lineages.Rp-uvo1 and Rp-uvo2 were expressed significantly higher in winged virginoparae than in wingless virginoparae in two kinds life cycle of R.padi.Under long-term rearing conditions,from the perspective of photoperiod,the expression levels of Rp-lwo,Rp-uvo1,Rp-uvo2,Rp-rho,and Rp-Co in wingless virginoparae of anholocyclic lineage under short-day condition were significantly higher than those under long-day condition;from the perspective of temperature,the expression levels of Rp-lwo?Rp-uvo1?Rp-uvo2?Rp-uvo4 in wingless virginoparae of anholocyclic lineage under low temperature were significantly lower than those under normal temperature,whilst there were no significant differences in the expression levels of Rp-uvo3,Rp-rho,and Rp-Co.The current results indicate that the expression of opsin genes has the characteristics of Sex differentiation,and is closely related to developmental stage,life cycle type and wing morph,also affected by the photoperiod and temperature.4.Effect of induced treatment(low temperature and short-day condition)on the expression of opsin genes in R.padi with different life cycle.To imitate the autumn climate condition,wingless virginoparaes of R.padi with holocyclic and anholocyclic life cycle were respectively raised for three generations under low temperature and short-day condition(12?,8L: 16D).Under induced conditions,the expression levels of Rp-lwo,Rp-uvo1,Rp-rho,and Rp-Co significantly increased,but Rp-uvo3 significantly decreased in expression,and there was no change in expression levels of Rp-uvo2 and Rp-uvo4,in holocyclic wingless virginoparaes.As for anholocyclic wingless virginoparaes,the expression levels of Rp-uvo1?Rp-uvo3?Rp-Co significantly decreased,but the remaining opsin genes didn't change in expression,under induced conditions.Our results show that R.padi with two different life cycles holds different survival strategies in response to low temperature and short-day condition in visual aspects. |
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