A horizontally acquired gene mediates insect cocoon pigmentation in the eri silkmoth, Samia ricini
- 1Jiangsu Key Laboratory of Sericultural and Animal Biotechnology, School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu 212100, China
- 2Key Laboratory of Silkworm and Mulberry Genetic Improvement, Ministry of Agriculture and Rural Affairs, The Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, Jiangsu 212100, China
- 3Guangdong Provincial Key Laboratory of Insect Developmental Biology and Applied Technology, Guangzhou Key Laboratory of Insect Development Regulation and Application Research, School of Life Sciences, South China Normal University, Guangzhou, Guangdong 510631, China
Abstract
Holometabolous insects make cocoons during larval–pupal metamorphosis to protect the pupal phase. The materials used for cocoon construction vary widely. Lepidopteran insects typically secrete silk to form cocoons, which display diverse colors. The eri silkworm, Samia cynthia ricini, is an economically important domesticated species that mostly produces white cocoons, with some varieties producing red cocoons. The enzyme kynureninase (KYNU), acquired from bacteria by horizontal gene transfer, has previously been implicated in insect coloration, while the tryptophan metabolite 3-hydroxyanthranilic acid (3-HAA) has been identified as a red pigment. However, exactly how KYNU is involved in cocoon pigmentation remains unclear. Here, we report that a horizontally transferred bacterial gene encoding KYNU regulates red cocoon formation. Metabolomic analysis revealed a high accumulation of 3-HAA in red cocoons, confirming its role as the primary pigment and associating the coloration with tryptophan metabolism. Quantitative real-time polymerase chain reaction (qPCR) analysis indicated that SrKYNU is highly expressed in the silk glands and significantly downregulated in the red cocoon strain compared to the white cocoon strain. Genomic sequencing identified a 141 bp deletion in the upstream regulatory region of KYNU in the red cocoon strain compared to the white cocoon strain. Dual-luciferase assays confirmed that this deletion significantly reduced promoter activity. CRISPR/Cas9 knockout of SrKYNU in the white-cocoon strain resulted in mutants producing red cocoons with elevated 3-HAA content. These findings reveal that the horizontally transferred gene SrKYNU exhibits tissue-specific expression and regulates cocoon coloration in S. ricini, illustrating that horizontal gene transfer can play an important role in regulating an insect physiological process.
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BibTeX
@article{guo2026horizontally,
title = {{A horizontally acquired gene mediates insect cocoon pigmentation in the eri silkmoth, Samia ricini}},
author = {Hui-Duo Guo and Zhong-Jie Zhang and Ming-Fa Ling and Chen-Xin Sun and Yu Guo and Xiang-Biao Liu and Ke-Sen Zhu and Hui Xiang and He-Ying Qian and An-Jiang Tan},
journal = {Zoological Research},
year = {2026},
month = sep,
doi = {10.24272/j.issn.2095-8137.2025.447},
url = {https://doi.org/10.24272/j.issn.2095-8137.2025.447},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - A horizontally acquired gene mediates insect cocoon pigmentation in the eri silkmoth, Samia ricini
AU - Hui-Duo Guo
AU - Zhong-Jie Zhang
AU - Ming-Fa Ling
AU - Chen-Xin Sun
AU - Yu Guo
AU - Xiang-Biao Liu
AU - Ke-Sen Zhu
AU - Hui Xiang
AU - He-Ying Qian
AU - An-Jiang Tan
PY - 2026
DA - 2026/09/18
JO - Zoological Research
DO - 10.24272/j.issn.2095-8137.2025.447
UR - https://doi.org/10.24272/j.issn.2095-8137.2025.447
AB - Holometabolous insects make cocoons during larval–pupal metamorphosis to protect the pupal phase. The materials used for cocoon construction vary widely. Lepidopteran insects typically secrete silk to form cocoons, which display diverse colors. The eri silkworm, Samia cynthia ricini, is an economically important domesticated species that mostly produces white cocoons, with some varieties producing red cocoons. The enzyme kynureninase (KYNU), acquired from bacteria by horizontal gene transfer, has previously been implicated in insect coloration, while the tryptophan metabolite 3-hydroxyanthranilic acid (3-HAA) has been identified as a red pigment. However, exactly how KYNU is involved in cocoon pigmentation remains unclear. Here, we report that a horizontally transferred bacterial gene encoding KYNU regulates red cocoon formation. Metabolomic analysis revealed a high accumulation of 3-HAA in red cocoons, confirming its role as the primary pigment and associating the coloration with tryptophan metabolism. Quantitative real-time polymerase chain reaction (qPCR) analysis indicated that SrKYNU is highly expressed in the silk glands and significantly downregulated in the red cocoon strain compared to the white cocoon strain. Genomic sequencing identified a 141 bp deletion in the upstream regulatory region of KYNU in the red cocoon strain compared to the white cocoon strain. Dual-luciferase assays confirmed that this deletion significantly reduced promoter activity. CRISPR/Cas9 knockout of SrKYNU in the white-cocoon strain resulted in mutants producing red cocoons with elevated 3-HAA content. These findings reveal that the horizontally transferred gene SrKYNU exhibits tissue-specific expression and regulates cocoon coloration in S. ricini, illustrating that horizontal gene transfer can play an important role in regulating an insect physiological process.
SN - 2095-8137
ER -