Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Targeting a Nuclear Anthranilate Synthase α-Subunit Gene to the Tobacco Plastid Genome Results in Enhanced Tryptophan Biosynthesis. Return of a Gene to Its Pre-Endosymbiotic Origin

Xing-Hai Zhang, Jeffrey E. Brotherton, Jack M. Widholm and Archie R. Portis, Jr.
Plant Physiology
Vol. 127, No. 1 (Sep., 2001), pp. 131-141
Stable URL: http://www.jstor.org/stable/4280066
Page Count: 11
  • Read Online (Free)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Targeting a Nuclear Anthranilate Synthase α-Subunit Gene to the Tobacco Plastid Genome Results in Enhanced Tryptophan Biosynthesis. Return of a Gene to Its Pre-Endosymbiotic Origin
Preview not available

Abstract

Anthranilate synthase (AS), the control enzyme of the tryptophan (Trp) biosynthetic pathway, is encoded by nuclear genes, but is transported into the plastids. A tobacco (Nicotiana tabacum) cDNA (ASA2) encoding a feedback-insensitive tobacco AS α-subunit was transformed into two different sites of the tobacco plastid genome through site-specific insertion to obtain transplastomic plants with normal phenotype and fertility. A high and uniform level of ASA2 mRNA was observed in the transplastomic plants but not in the wild type. Although the plants with the transgene insertion at ndhF-trnL only expressed one size of the ASA2 mRNA, the plants with the transgene incorporated into the region between accD and open reading frame (ORF) 184 exhibited two species of mRNA, apparently due to readthrough. The transplastomic plants exhibited a higher level of AS α-subunit protein and AS enzyme activity that was less sensitive to Trp-feedback inhibition, leading to greatly increased free Trp levels in leaves and total Trp levels in seeds. Resistance to an AS inhibitor, 5-methyl-Trp, was found during seed germination and in suspension cultures of the transplastomic plants. The resistance to the selection agent spectinomycin and to 5-methyl-Trp was transmitted maternally. These results demonstrate the feasibility of modifying the biosynthetic pathways of important metabolites through transformation of the plastid genome by relocating a native gene from the nucleus to the plastid genome. Very high and uniform levels of gene expression can be observed in different lines, probably due to the identical insertion sites, in contrast to nuclear transformation where random insertions occur.

Page Thumbnails

  • Thumbnail: Page 
131
    131
  • Thumbnail: Page 
132
    132
  • Thumbnail: Page 
133
    133
  • Thumbnail: Page 
134
    134
  • Thumbnail: Page 
135
    135
  • Thumbnail: Page 
136
    136
  • Thumbnail: Page 
137
    137
  • Thumbnail: Page 
138
    138
  • Thumbnail: Page 
139
    139
  • Thumbnail: Page 
140
    140
  • Thumbnail: Page 
141
    141