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ABSTRACT
Kerria lacca is commercially harnessed for lac resin, dye and wax. This study is an attempt towards identifying the possible pathway and genes involved in the biosynthesis of the lac dye. It is proposed that lac insects employ polyketide pathway catalysed by polyketide synthase to produce laccaic acid D, a common precursor molecule for the biosynthesis of other lac dye constituents. Post-PKS tailoring enzymes are also involved in the alteration of polyketide chains. Thirteen related genes were identified and sequenced in this study.
Key words: Lac insect, laccaic acid, lac dye, polyketide, biosynthesis.
INTRODUCTION
Indian lac insects, Kerria lacca, belonging to the family Tachardiidae (=Kerriidae) which constitutes a specialized group in Superfamily Coccoidea (Hemiptera: Sternorrhyncha), show diverse body colours from crimson to yellow, and cream to albino (white). Colour difference in lac insect is inherited as a unit character and crimson is dominant to yellow (Sharma and Ramani, 2011). Wild type insect possesses crimson body colour due to the presence of a complex of closely resembling water-soluble polyhydroxy-anthraquinones (Fig. 1), collectively called as lac dye. Laccaic acids A and B are the principle components of lac insect body colouration (Bhide et al., 1969; Burwood et al., 1967; Oka et al., 1998a, 1998b; Pandhare et al., 1966, 1967, 1969); whereas laccaic acid C, D and E have been isolated in little quantities (Mehandale et al., 1968; Rama Rao et al., 1968). The anthraquinone represented by laccaic acid D, is assumed as a parent compound for the biogenesis of all other anthraquinone pigment compounds found in wild type lac insects, such as laccaic acid A, B, C and E; and those found in related coccoids (for example, kermesic acid and carminic acid from Kermes ilicius and Dactylopius coccus, respectively). Hu et al. (2011) isolated laccaic acid F from the Thai sticklac, K. chinensis. The amino acid residue in laccaic acid C appears to be derived from tyrosine by phenolic coupling with a polyhydroxyanthraquinone compound. Yellow mutant lac insects containing laccaic acid D have been reported (Chauhan, 1967; Negi et al., 1945) in both rangeeni and kusmi infrasubspecific forms of K. lacca, K. albizziae and K. fici. The cream-coloured insect shows a very light yellow body colour (Ramani, 2011). White mutants lack both body and resin...