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Molecular characterization of two anthranilate synthase alpha subunit genes in Camptotheca acuminata

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Abstract

The potent anticancer and antiviral compound camptothecin (CPT) is a monoterpene indole alkaloid produced by Camptotheca acuminata. In order to investigate the biosynthetic pathway of CPT, we studied the early indole pathway, a junction between primary and secondary metabolism, which generates tryptophan for both protein synthesis and indole alkaloid production. We cloned and characterized the alpha subunit of anthranilate synthase (ASA) from Camptotheca (designated CaASA), catalyzing the first committed reaction of the indole pathway. CaASA is encoded by a highly conserved gene family in Camptotheca. The two CaASA genes are differentially regulated. The level of CaASA2 is constitutively low in Camptotheca and was found mainly in the reproductive tissues in transgenic tobacco plants carrying the CaASA2 promoter and β-glucuronidase gene fusion. CaASA1 was detected to varying degrees in all Camptotheca organs examined and transiently induced to a higher level during seedling development. The spatial and developmental regulation of CaASA1 paralleled that of the previously characterized Camptotheca gene encoding the beta subunit of tryptophan synthase as well as the accumulation of CPT. These data suggest that CaASA1, rather than CaASA2, is responsible for synthesizing precursors for CPT biosynthesis in Camptotheca and that the early indole pathway and CPT biosynthesis are coordinately regulated.

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Abbreviations

ASA:

Anthranilate synthase alpha

CPT:

Camptothecin

DPI:

Days post imbibition

GUS:

β-Glucuronidase

TDC:

Tryptophan decarboxylase

TSB:

Tryptophan synthase beta subunit

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Acknowledgements

We thank members of McKnight laboratory for their helpful discussion and assistance during the course of this work and Craig Nessler and Argelia Lorence for critically reading the manuscript. This work was supported by a grant from the National Institutes of Health (R01-CA-57592).

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Authors and Affiliations

  1. Department of Molecular Genetics and Cell Biology, Erman Biology Center, The University of Chicago, 1103 East 57th Street, Chicago, IL, 60637, USA

    Hua Lu

  2. Department of Biology, Texas A&M University, College Station, TX, 77843-3258, USA

    Elizabeth Gorman & Thomas D. McKnight

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  1. Hua Lu
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  2. Elizabeth Gorman
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  3. Thomas D. McKnight
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Correspondence to Thomas D. McKnight.

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Lu, H., Gorman, E. & McKnight, T.D. Molecular characterization of two anthranilate synthase alpha subunit genes in Camptotheca acuminata. Planta 221, 352–360 (2005). https://doi.org/10.1007/s00425-004-1450-z

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