THE PLANT CELL, Vol 4, Issue 9 1063-1074, Copyright © 1992 by American Society of Plant Biologists
Expression of a Self-Incompatibility Glycoprotein (S2-Ribonuclease) from Nicotiana alata in Transgenic Nicotiana tabacum
J. Murfett, E. C. Cornish, P. R. Ebert, I. Bonig, B. A. McClure and A. E. Clarke
Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, Victoria 3052, Australia
In Nicotiana alata, self-incompatibility is controlled by a single locus,
designated the S-locus, with multiple alleles. Stylar products of these
alleles are ribonucleases that are secreted mainly in the transmitting
tract tissues. N. tabacum plants were transformed with constructs
containing the S2-cDNA and genomic S2-sequences from N. alata that were
linked to the cauliflower mosaic virus 35S promoter. Unlike other genes
controlled by this promoter, the genes were expressed most highly in mature
floral organs. This pattern of expression was observed at both the protein
and RNA levels. The S2-glycoprotein was detected in the stylar transmitting
tract tissues of the transgenic plants. The transgene product was secreted,
had ribonuclease activity, and was glycosylated with the correct number of
glycan chains. However, the maximum level of S2-glycoprotein in styles of
the transgenic plants was approximately 100-fold lower than that found in
N. alata styles carrying the S2-allele. Perhaps because of this lower
protein level, the plants showed no changes in the incompatibility
phenotype.
