Cloning and Characterization Of N-Methyltransferase Gene associated with Caffeine Biosynthesis in Coffee

Satyanarayana, K. V. (2005) Cloning and Characterization Of N-Methyltransferase Gene associated with Caffeine Biosynthesis in Coffee. PhD thesis, University of Mysore.

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Abstract

Caffeine (1,3,7-trimethyl xanthine) is found in seeds and leaves of coffee, cola, mate and tea. Along with other methylxanthines, including theobromine, paraxanthine and methyluric acids, caffeine is a member of a group of compounds known collectively as purine alkaloids. The biosynthetic pathway of theobromine and caffeine has been the subject of much study over the years. Caffeine is synthesized through three sequential steps involving methylation of xanthine derivatives at positions 7-N, 3-N and 1-N(xanthosine → 7-Methylxanthosine → 7-Methylxanthine → Theobromine → Caffeine),catalyzed by N -methyltransferases that use S-Adenosyl-L-Methionine as methyl donor.A survey of literature suggested that the N-methyltransferases (NMTs) that are involved in the caffeine biosynthetic pathway in coffee comprise a multigene family. Several cDNA clones for NMTs from coffee have been reported. However, there are no reports on the genomic sequences for the NMT genes. The studies on NMT gene structure and organisation are lacking. Therefore, it was envisaged that PCR based genomic cloning of the NMT genes could provide valuable information regarding the number and size of introns and exons present in NMT genes. The study of introns and exons could possibly shed light on the mechanisms for origin of NMT multigene family in coffee and possible functional divergence among different members of the gene. The survey of literature and patents indicated a distinct lacuna in the studies related to NMT gene regulation. The isolation of promoter for the NMT genes has not been hitherto reported and hence it became one of the major objectives of this investigation. The promoter isolation could help in understanding the NMT gene regulation and also open up the possibilities of regulating caffeine content in coffee plants. There are wide variations in the caffeine contents of different coffee species, the reasons for which are unknown. Very little is known about the NMT genes in Coffea species other than C. arabica. It may be speculated that differential transcription of various NMT genes could be one of the reasons for such variations in the caffeine content. Study of possible polymorphisms for the NMT genes and their corresponding promoters in different Coffea species could be vital in understanding differential transcription of various NMT genes. The production of transgenic caffeine deficient coffee plants by RNAi using specific region of the theobromine synthase gene has been reported earlier, wherein spreading of silencing to other NMT genes was observed. The use of a conserved region common to all the NMT genes should theoretically result in silencing of all the NMT genes. Moreover, other posttranscriptional gene silencing strategies were not explored for caffeine down regulation. The use of conserved region of NMT genes for different posttranscriptional gene silencing strategies could be a viable option for obtaining phenotypes with desirable purine alkaloid profiles.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Caffeine Biosynthesis Coffee N-Methyltransferase Biosynthesis
Subjects:	500 Natural Sciences and Mathematics > 07 Life Sciences > 03 Biochemistry & Molecular Biology 600 Technology > 05 Chemical engineering > 01 Biotechnology and Bioengineering 600 Technology > 07 Beverage Technology > 03 Cocoa
Divisions:	Plant Cell Biotechnology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	22 Dec 2006
Last Modified:	03 Jul 2015 08:14
URI:	http://ir.cftri.res.in/id/eprint/357

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