Genetics of Silk Moth Domestication

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Known as the “queen of fibers,” silk has a long and varied history that dates back more than 5,000 years to ancient China. Its narrative covers the change from the wild Silk Moth (Bombyx mandarina) to the domesticated Silk Moth (Bombyx mori), providing an intriguing look at both the adaptability of nature and human creativity.

Silk Moth Domestication

  • Ancient Origins: The art of sericulture was born when people in China started domesticating silk moths from the wild Bombyx mandarina.
  • Worldwide Distribution: The domesticated Bombyx mori moth, which is much larger than its wild counterpart, is currently found all over the world, including India.
  • Silk Powerhouse: India is the world’s secondlargest producer of raw silk, after China, thanks to its exceptional silk producing skills.

Silkworms and Mulberry Leaves

  • Caterpillars, also referred to as silkworms, only consume the leaves of mulberry bushes (genus Morus).
  • Building of Cocoons: To create larger cocoons, the domesticated silk moth extrudes silk fibers that can reach lengths of up to 900 meters. These caterpillars have adapted to human care by losing their pigmentation and capacity to fly.

Diversity in Silk

  • Wild Silk Varieties: Various moth species, such as Antheraea assama, Antheraea mylitta, and Samia cynthia ricini, are the source of “wild” silks, which include muga, tasar, and eri.
  • Characteristics that Contrast: The threads of non-mulberry silks are coarser, tougher, and shorter than those of mulberry silks.

The Enigmatic Cocoon Colors

  • Natural Variations: Yellow-red, flesh, gold, pale green, deep green, and white are just a few of the striking hues that domesticated silk moth cocoons can display.
  • Human Influence: In an effort to produce colored silks, selective breeding for cocoons with varied colors was used; however, because these pigments are water-soluble, they eventually fade. Colored silks are produced for the market using acid dyes.
  • The Sources of Pigments: Mulberry leaves generate carotenoids and flavonoids, which are the source of pigments found in cocoons. These substances are consumed by silkworms, whereupon they attach themselves to silk proteins and spin into a single strand.

Mutant Strains and Genetic Insights

  • Important Resource: Mutations in the genes controlling the intake, transport, and alteration of pigments have given rise to mutant strains of silk moths.
  • Diversity from Domestication: China and Japan have largely investigated the molecular underpinnings of silk domestication, with significant contributions from Indian scientists.
  • Decoding Cocoon Colors: A Model Emerges
  • Genetic Factors: A model describing how various mutations result in a variety of cocoon hues was put out by researchers at Southwest University in Chongqing, China.
  • Important Genes: Different cocoon hues result from differences in pigment absorption and transportation, which is mediated by genes like as Y, C, F, Rc, and Pk.
  • Green Cocoon Mystery: When flavonoids are absorbed but carotenoids are not, mutations in the Y gene cause green cocoons. The amount of green is determined by mutations in other genes that impact the absorption of flavonoids.
  • Flavonoid Cluster: The absorption of flavonoids in cocoons is influenced by a group of closely linked genes.

Gene Manipulation and Domestication

  • Hybrid Offspring: By crossing domesticated and ancient silk moths, researchers have produced hybrid moths.
  • Apontic-like Gene: Variations in melanin production between domesticated and wild silk moths were shown to be caused by mutations in the apontic-like gene.
  • Gene Regulation Sequence Variations: These sequence variations determine the location and timing of gene activation or deactivation.

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