Project	Genomics of Wild Silkmoths
Investigators PhD Scholars Technical Staff	KP Arunkumar
Collaborator	HA Nagarajaram, CDFD
Funding Agency	Department of Biotechnology, Govt of India, New Delhi

Genomics of Wild Silkmoths

Introduction

Silks fall into two main types, the mulberry and the non-mulberry silks. The classification is based on the kind of silkworms that are used as raw materials for silk production. Almost all the varieties of mulberry silks are derived from the domesticated silkworm Bombyx mori. The non-mulberry silks often called the 'Wild Silks' are derived from the silkworms which are not domesticated. 'Wild Silks' generally come in natural colours - cream, beige, brown and gold. They are not only user-friendly but also healthy owing to their porous texture and thermal properties. Tribal communities and economically disadvantaged sections of the society are the primary rearers of these silkworms.

Silkmoth species include Bombyx mori of family Bombycidae and wild silkmoths that belong to Saturniidae, Antheraea mylitta (Indian tropical tasar silkmoth), (Chinese oak tasar silkmoth), A. roylei (Indian oak tasar silkmoth), A. assama (Indian golden silkmoth), A. yamamai (Japanese oak silkmoth), A. pernyi (Chinese Oak Silkmoth) and Philosamia cynthia ricini (Indian castor silkmoth). Silk production based on these moths, especially B. mori, A. pernyi, A. mylitta and A. assama plays important role in rural economies of many developing nations.

Non-mulberry sericigenous fauna belonging to the family Saturniidae are mostly wild Silkmoths. The Indian tasar silkworm Antheraea mylitta is a natural fauna of tropical India, represented by 19 ecoraces. Antheraea assama (Muga silkworm) (n= 15) is a wild silk moth mentioned in early literature as early as 1662 BC. It is widely distributed and cultured in North-Eastern India particularly in Assam. The golden-yellow muga silk is secreted by this semi-domesticated multivoltine species. Larvae fed on mejankori leaves (Litsea citrata) produces a kind of silk known as mejankori silk, which is favoured for its durability, lustre and creamy white shade. Antheraea yamamai is a native of Japan with 31 chromosomes. Samia cynthia ricini (n= 13) a multivoltine silkworm commonly called as 'eri silkworm' is known for its white or brick-red eri silk. It is distributed in North-Eastern part of India. Its other ecoraces (~16) are distributed across the palaearctic and indo-australian biogeographic regions. Antheraea pernyi (n=49) is originated in Southern China, dating back to the Han and Wei dynasties. Antheraea roylei (n=30,31,32) is distributed along the Sub-Himalayan belt of India. Antheraea proylei (n=49) is a successful hybrid of the Antheraea roylei with its chinese counterpart. Antheraea pernyi.

In the past years, focus of our lab was on characterization of mariner like elements in wild silkmoths. Mariner like elements (MLEs) are widely distributed type II transposons with an open reading frame (ORF) for transposase. We studied comparative phylogenetic evolution and inverted terminal repeat (ITR) conservation of MLEs from Indian saturniid silkmoth, Antheraea mylitta with other full length MLEs submitted in the database. Full length elements from A. mylitta were inactive with multiple mutations. Many conserved amino acid blocks were identified after aligning transposase sequences. Mariner signature sequence, DD(34)D was almost invaB-riB-able although a few new class of elements had different signatures. A. mylitta MLEs (Anmmar) get phylogeneB-tiB-cally classified under cecropia subfamily and cluster closely with the elements from other Bombycoidea superfamily members implying vertical transmission from a common ancestor. ITR analysis showed a conserved sequence of AGGT(2-8N)ATAAGT for forward repeat and AGGT(2-8N)ATGAAAT for reverse repeat. These results and additional work may help us to understand the dynamics of MLE distribution in A. mylitta and construction of appropriate vectors for mariner mediated transgenics.

Functional genomics

The use of genome sequences to solve biological problems has even been afforded its own label, it's called functional genomics. Our lab has employed silkmoths to study the functional genomics of lepidopteran species. A. assama, one of the economically important wild silkmoths whose genome is among the least understood is unique among saturniid moths.

Native of Assam and named after Assamese word "Muga" which indicates the amber (brown) colour of cocoon. It belongs to same family as Tussar. It is popular for its natural golden colour, glossy fine textures and durability. Muga silk is produced by A. assama, which is an endemic species prevalent in the Brahmaputra valley and adjoining hills. Muga silkworm is a polyphagous insect, which feeds on leaves of Som, Soalu and other plants, which grows abundantly in Brahmapautra valley.

Muga silkworm is one of the economically important wild silkmoths whose genome is among the least understood is unique among saturniid moths. The silk proteins of this species have not been studied so far despite their unique properties of providing golden luster to the silk thread. In view of this, it is important to look at the transcriptome of this unique species in comparison with other pecies, which will throw light on the basic and applied aspects of domesticated and wild silkmoths. Comparative studies on expressed sequences of the B. mori and wild silkmoths with the other published genome sequences of insects and other model organisms could uncover lepidoptera-specific genes.

In the present study, we envisaged to construct and characterize ESTs from wild silkmoth, A. assama and carryout comparative analysis of the ESTs with all other EST databases including Drosophila and B. mori. Since the chromosomal number is lower in A. assama (n=15) as compared to the model lepidopteran chromosome number of n=31, it is easy to construct physical map as well as identifying molecular markers via ESTs. Thus by EST sequencing even if only 10% of these genes are identified which are of any consequence to the unique character, then 600 new genes will become available from this unique wild silkmoth. This would enable us to decipher some important genes involved in antimicrobials, antifungals, silk-fibre quality, sex determination and developmental genes involved in pattern formation that are unique to the wild silkmoths.

Isolation of Microsatellites from Wild Silkmoths

We are working on genetic characterization and population genetics of wild silkmoths. For population genetic studies we are isolating microsatellite markers from wild silkmoths, A. mylitta and A. assama.