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Research Papers
Introduction
Lac is the only commercial resin of animal origin and is a natural polymer derived from the resinous secretions of specialized epidermal glands distributed throughout the body surface of phytosuccivorous lac insects (Hemiptera: Coccoidea: Tachardiidae ( = Kerridae)). The resinous covering of lac not only protects the insects but also fixes them to the twig, facilitating their sedentary and phytophagous mode of nutrition. The Indian lac insect, Kerria lacca (Kerr) is the principal species used for lac production in India, which is the global leader in lac production.
The constituent acids of lac resin fall under two categories: (i) hydroxy fatty acids, principally aleuritic acid (9,10,16-trihydroxyhexadecanoic acid), and (ii) hydroxy sesquiterpenic acids having the rare cedrene skeleton (Prasad, 2010). Other constituent acids that have been isolated from lac resin are butolic, shellolic, epishellolic, laksholic, epilaksholic, laccijalaric, laccishellolic, laccilaksholic, epilaccishellolic and epilaccilaksholic acids. It has been suggested that pure lac resin of molecular weight 2194 g/mol (Prasad, 2010) is made up of aleuritic acid and terpenic acids (jalaric/laccijalaric acid and derived dicarboxylic acids) at a ratio of 1:1. Among the four terpenic acids, there are three jalaric/epishellolic acids and one laccijalaric/epilaccishellolic acid (Singh et al., 1974). The present study is the first attempt made to understand possible pathways related to the biosynthesis of complex lac resin and the genes involved. The genetics of lac biosynthesis is still unexplored and needs to be paid more attention to identify the genes involved and to deduce the biosynthetic pathway.
Biosynthesis of lac resin
Sesquiterpene biosynthesis
A number of different sesquiterpene compounds have been identified across a wide range of taxa with a variety of biological roles. The sesquiterpene diversity in biological systems arises via two ways: (i) the biosynthetic sequence involved in the assembly of the 15-carbon sesquiterpene backbone and (ii) the variation in the addition of functional groups and substituents (Chappell and Coates, 2010).
Sesquiterpene biosynthesis in lac insects has hitherto been unexplored, but it is probably similar to that reported in other insects. As has been described previously, the insects synthesize terpenes in the cytosol through the mevalonic acid (MVA) pathway or the HMG-CoA reductase pathway (Bede et al., 2001). In the first step, acetate (as...