Journal Article

Inheritance, expression, and silencing of a chitinase transgene in rice

Chareonpornwattana, S, Thara, K.V, Wang, L, Datta, S.K, Panbangred, W, Muthukrishnan, S

1999

Overview

The inheritance and expression of a transgene locus consisting of multiple copies of a rice chitinase gene under the control of the CaMV 35S promoter was studied in the T3 and T4 generations of a transformed line that expressed the chitinase at a high level. All T3 progeny of a homozygous T2 parent expressed the chitinase constitutively at 3 weeks after germination, but a proportion of the progeny had undetectable levels of chitinase 8 weeks after germination, indicating silencing of the transgene. Transgene silencing was also observed among progeny of a hemizygous parent. However, we did not observe chitinase gene silencing among progeny of another homozygous line that expressed the transgenic chitinase at a five- to tenfold lower level. Thus, expression level, rather than copy number, of the transgene appears to be critical for silencing. Silencing was observed in the leaf, sheath, and root tissues of the plant, indicating that it is not restricted to specific tissues. Silencing was first observed in the youngest leaves and only later in the oldest leaves of the same plant. There was co-silencing of the selectable marker gene, hpt, which is also driven by the CaMV 35S promoter. Unlike the two transgenes (chitinase and marker), the resident homologous chitinase gene with seed-specific expression and two nonhomologous chitinase genes induced in the leaves upon pathogen infection were not silenced. The silent phenotype was inherited in the T4 generation plants, while progeny of expressing plants exhibited silencing. The chitinase transgene appeared intact, and no evidence for gross alterations or methylation of CCGG sites was found. The silent phenotype could not be reversed by treatment with 5-azacytidine. Northern blot analysis and nuclear run-on transcription studies indicated that silencing occurred at the transcriptional level. The implications of transgene silencing in genetic engineering of monocot plants for disease resistance are discussed.

• Publisher: Springer,Springer Nature B.V
• Subject: Biochemistry / Biological and medical sciences / Biotechnology / Cauliflower mosaic virus / Chitinase / Classical genetics, quantitative genetics, hybrids / direct DNA uptake / drug resistance / enzyme activity / experimental infections / Fundamental and applied biological sciences. Psychology / fungal diseases of plants / gene expression / Gene silencing / Genes / Genetic aspects / Genetic engineering / genetic regulation / Genetic technics / genetic transformation / Genetics of eukaryotes. Biological and molecular evolution / Genotype & phenotype / hpt gene / hygromycin B / hygromycin phosphotransferase / inheritance (genetics) / kinases / leaf sheaths / Leaves / Methods. Procedures. Technologies / Oryza sativa / phosphotransferases (kinases) / Plant genetics / Plant immunology / promoter regions / Pteridophyta, spermatophyta / recombinant DNA / reporter genes / Rice / roots / Thanatephorus cucumeris / transcription (genetics) / Transgenic animals and transgenic plants / Transgenic plants / Vegetals