| Insect compound eye is an important sense organ to receive signal and communicate with the outside world, which plays important role in the feeding, avoiding the enemies and courtship. The pigment in compound eye can absorb and reflect the light selectively, which leads to a variety of different colors in the compound eye.Eye color mutants appear occasionally in wild-type strains. Many natural mutants of eye color have been described in about40kinds of insects from Diptera, Hemiptera, Coleoptera and Lepidoptera, including red, white, yellow and so forth. Among them, red and white are the most common colors. Different compound eye color has some effects on the some physiological functions and biological characteristics of insects.Nilaparvata lugens Stal (Brown planthopper, BPH) is one of the most important pests on rice. In our laboratory, a few individuals with red-eye were found in BPH wild type strain with all brown-eye individuals. In the present study, BPH red-eye strain was selected from the wild-type strain for more than ten generations. The differences in biological characteristics between two strains and the mechanisms of eye color differentiation in the biochemical and molecular ascepts were studied in present study.1. Selection of the red-eye strain and the differences in biological characteristics between two strainsWhen rearing BPH brown-eye wild type strain in laboratory, the red-eye individuals were found in female adults in2009. After selection and purification for more than ten generations, the red-eye strain was obtained with all individuals of eye-color. The color of the compound eye in the red-eye strins was in the obvious red from nymph to adult. The wild-type brown-eye strain and the red-eye strain were used in the following experiments. Different combinations of mating ((?)×(?) B×B, B×R, R×B, R×R) were designed to test the effects of the eye-color change in the biological characteristics of BPH. The newly hatched nymph was counted every day after eight days of mating. When there were no more newly hatched nymphs, rice stems were dissected to count invalid eggs. The fertility, egg variability and nymph survival rate were recorded and calculated. The results showed that fecundity, egg hatchability and3-5instar nymphs survival rate were no significant different between two strains, but the1-3instar nymphs survival rate in the red-eye strain was significantly lower than that of the brown-eye strain (P<0.05). Collecting and weighing individual honeydew of different strains was done to reveal the virulence change after the eye-color differentiation. The results showed that the single female’s honeydew excretion of brown-eye wild-type strain was0.1018±0.0265mg and0.0904±0.0283mg in the red-eye strain, which was not with significant difference.In addition, as a distinct and visible genetic marker, the eye-color can be used as a marker of mating behavior of insects. In the present study, the red-eye was used as a marker to study on the ability to multiple mating of single male or female. Two mating combinations RR×RR&BB and RR&BB×RR ((?)×(?)) were designed. The results showed that both of male and female adults could perform multiple mating and the male had the stronger ability of multiple mating than the female.2. Genetical law and biochemical mechanisms of eye color differentiation in BPHThe changing in eye color of BPH is a heritable change. By designing a series of cross experiments and counting eye-color separation ratio of offspring, the genetical law was determined for the eye color differentiation. The results showed that the compound eye color of F1generation of pure or reciprocal crosses were all brown, the eye-color separation ratio of F2was close to3:1(brown:red), the eye-color separation ratio of Ft (the backcrossed offspring of F1and parental) was close to1:1, and the eye color of the strains selfing progency was the same as their parents. These results indicated that the BPH red eye differentiation was in autosomal recessive inheritance controlled by a pair alleles, which in full compliance with Mendelian autosomal recessive inheritance laws.The pigment contents were tested in two strains and the offsprings of different mating combinations ((?)×(?):BXB, BXR, RXB, R×R). The results showed that, no matter females or males, both xanthommatin and pteridine content in the individuals of B X B were significantly higher than that in the individuals of R X R. For xanthommatin, the content of R×R was only36.3%(female) and67.4%(male) of B×B. For pteridine, the content of R×R was73.4%(female) and70.9%(male) of B×B. The reduction in the level and the change in the proportion of the two pigments might be the biochemical basis for the eye color differentation. 3. Sequence diversity and expression profiles of important genes encoding xanthommatin synthases and transporter proteins in different eye-color individualsTryptophan dioxygenase (TO) gene vermilion and kynurenine3-hydroxylase (KMO) gene cinnabar are two important genes in the biosynthetic pathway (tryptophan way) of xanthommatin. The white and scarlet genes (encoding ABC transporter proteins White and Scarlet), transporting xanthommatin and/or its precursors across membrane, were also tested. By comparing the amino acid sequences between individuals from the red-eye and brown-eye strains, a convserved mutation was found in Scarlet protein, which was denoted as M131I mutation corresponding to the amino acid site in Scarlet protein of Drosophila melanogaster.The expression difference between two strains was determined by qRT-PCR. The quantitative results showed that relative expression levels of vermilion gene and scarlet gene in the red-eye individuals were4.86times and1.73times than that in the brown-eye individuals, with the significant difference (P<0.05). By contrast, there were no significant differences in cinnabar gene and white gene between the red and brown-eye individuals. |
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