Article

Molecular Biology Reports

, Volume 40, Issue 5, pp 3631-3639

Green cocoons in silkworm Bombyx mori resulting from the quercetin 5-O-glucosyltransferase of UGT86, is an evolved response to dietary toxins

  • Xu XuAffiliated withNational Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow UniversityDepartment of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University
  • , Meng WangAffiliated withNational Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow UniversityDepartment of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University
  • , Ying WangAffiliated withNational Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow UniversityDepartment of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University
  • , Yanghu SimaAffiliated withNational Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow UniversityDepartment of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University
  • , Dayan ZhangAffiliated withNational Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow UniversityDepartment of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University
  • , Juan LiAffiliated withCollege of Forestry, Shandong Agricultural University
  • , Weiming YinAffiliated withLaboratory Animal Centre, Medical College, Soochow University
  • , Shiqing XuAffiliated withNational Engineering Laboratory for Modern Silk, Institute of Agricultural Biotechnology & Ecology, Soochow UniversityDepartment of Applied Biology, School of Biology and Basic Medical Sciences, Medical College, Soochow University Email author 

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Abstract

The glycosylation of UDP-glucosyltransferases (UGTs) is of great importance in the control and elimination of both endogenous and exogenous toxins. Bm-UGT10286 (UGT86) is the sole provider of UGT activity against the 5-O position of quercetin and directly influences the formation of green pigment in the Bombyx cocoon. To evaluate whether cocoon coloration evolved for mimetic purposes, we concentrated on the expression pattern of Ugt86 and the activities of the enzyme substrates. The expression of Ugt86 was not only detected in the cocoon absorbing and accumulating tissues such as the digestive tube and silk glands, but also in quantity in the detoxification tissues of the malpighian tubes and fat body, as well as in the gonads. As in the green cocoon strains, Ugt86 was clearly expressed in the yellow and white cocoon strains. In vitro, the fusion protein of UGT86 showed quercetin metabolic activity. Nevertheless, Ugt86 expression of 5th instar larvae was not up-regulated in the silk gland by exogenous quercetin. However, it was significantly up-regulated in the digestive tube and gonads (P < 0.05). A similar result was observed in experiments where larvae were exposed to rutin, an insect resistance inducer and growth inhibitor typically found in plants, and to 20-hydroxylecdysone (20E), an insect endocrine and plant source hormone. On the contrary, up-regulated Ugt86 expression was almost nil in larvae exposed to juvenile hormone III (P > 0.05). The results of HPLC revealed that a new substance was formed by mixing 20E with the recombinant UGT86 protein in vitro, indicating that the effect of Ugt86 on 20E was similar to that on exogenous quercetin derived from plant food, and that the effect probably initiated the detoxification reaction against rutin. The conclusion is that the reaction of Ugt86 on the silkworm cocoon pigment quercetin is not the result of active mimetic ecogenesis, but derives from the detoxification of UGTs.

Keywords

UDP-glucosyltransferase Cocoon coloration Biological detoxification Co-evolution Bombyx mori