Planta 212: 243-249 (2001)
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ß-1,3-Glucanase and chitinase transgenes in hybrids
show distinctive and independent patterns of posttranscriptional gene
silencing
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Christian Kunz, Hanspeter Schöb, Gerd Leubner-Metzger, Eugene
Glazov, Frederick Meins Jr
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Friedrich-Miescher Institute, Box 2543, CH-4002 Basel, Switzerland
Received: 26 February 2000 / Accepted: 17 May 2000
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Abstract. Nicotiana sylvestris Speg. & Comes transformed
with a tobacco class-I ß-1,3-glucanase (GLU I) cDNA. Driven by CaMV
35S RNA expression signals exhibits posttranscriptional gene silencing (PTGS)
which is triggered between the cotyledon and two-leaf stages of seedling
development and is postmeiotically reset to the high-expressing state during
seed development. The incidence of GLU I PTGS in sibling plants differed
for the two different transformants tested and increased with the number
of T-DNA loci. Comparison of host class-I and class- II ß-1,3-glucanase
gene expression suggests that a similarity of 60-70% in the coding-region
is required for PTGS of the homologous host genes. The GLU I transformants
exhibited a spatial gradient in PTGS, in which expression of the silent
phenotype gradually increased in successive leaves toward the bottom of
the plant. In contrast, transformants carrying an unrelated tobacco class
I chitinase (CHN I) cDNA in the same expression vector exhibited discontinuous
patterns of PTGS with adjacent high-expressing and silent leaves. The GLU
I- and CHN I- specific patterns were maintained in hybrids homozygous for
both T-DNA's indicating that two different transgenes present in the same
genome can exhibit independent and distinctive patterns of PTGS. This implies
that the nature of the transgene rather than a general pre-pattern of competence
for PTGS or propagation of the silent state are important for pattern determination.
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