Document Detail

Regulated inactivation of homologous gene expression in transgenic Nicotiana sylvestris plants containing a defense-related tobacco chitinase gene.
MedLine Citation:
PMID:  1281514     Owner:  NLM     Status:  MEDLINE    
The class I chitinases are vacuolar proteins implicated in the defense of plants against pathogens. Leaves of transgenic Nicotiana sylvestris plants homozygous for a chimeric tobacco (Nicotiana tabacum) chitinase gene with Cauliflower Mosaic Virus (CaMV) 35S RNA expression signals usually accumulate high levels of chitinase relative to comparable leaves of non-transformed plants. Unexpectedly, some transgenic plants accumulated lower levels of chitinase than nontransformed plants. We call this phenomenon silencing. The incidence of silencing depends on the early rearing conditions of the plants. When grown to maturity in a greenhouse, approximately 25% of plants raised as seedlings in closed culture vessels were of the silent type; none of the plants raised from seed in a greenhouse showed this phenotype. Silencing is also developmentally regulated. Plants showed three patterns of chitinase expression: uniformly high levels of expression in different leaves, uniformly low levels of expression in different leaves, and position-dependent silencing in which expression was uniform within individual leaves but varied in different leaves on the same plant. Heritability of the silent phenotype was examined in plants homozygous for the transgene. Some direct descendants exhibited a high-silent-high sequence of activity phenotypes in successive sexual generations, which cannot be explained by simple Mendelian inheritance. Taken together, the results indicate that silencing results from stable but potentially reversible states of gene expression that are not meiotically transmitted. Gene-specific measurements of chitinase and chitinase mRNA showed that silencing results from co-suppression, i.e. the inactivation of both host and transgene expression in trans. The silent state was not correlated with cytosine methylation of the transgene at the five restriction sites investigated.
C M Hart; B Fischer; J M Neuhaus; F Meins
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Molecular & general genetics : MGG     Volume:  235     ISSN:  0026-8925     ISO Abbreviation:  Mol. Gen. Genet.     Publication Date:  1992 Nov 
Date Detail:
Created Date:  1993-01-21     Completed Date:  1993-01-21     Revised Date:  2006-05-01    
Medline Journal Info:
Nlm Unique ID:  0125036     Medline TA:  Mol Gen Genet     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  179-88     Citation Subset:  IM    
Friedrich Miescher-Institut, Basel, Switzerland.
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MeSH Terms
Base Sequence
Chitinase / genetics*
DNA / genetics,  isolation & purification
Gene Expression Regulation*
Plants / genetics*
Plants, Genetically Modified
Plants, Toxic*
RNA / genetics,  isolation & purification
Tobacco / enzymology*,  genetics*
Reg. No./Substance:
0/Codon; 63231-63-0/RNA; 9007-49-2/DNA; EC 3.1.-/Ribonucleases; EC

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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