THE PLANT CELL, Vol 1, Issue 5 483-491, Copyright © 1989 by American Society of Plant Biologists
Sequence Variability of Three Alleles of the Self-Incompatibility Gene of Nicotiana alata
M. A. Anderson, G. I. McFadden, R. Bernatzky, A. Atkinson, T. Orpin, H. Dedman, G. Tregear, R. Fernley and A. E. Clarke
Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, Victoria 3052, Australia
Three alleles of the self-incompatibility gene of Nicotiana alata have been
cloned and sequenced. A comparison of the sequences shows a surprisingly
low level of homology (56%) and the presence of defined regions of homology
and variability. The homologous regions include the N-terminal sequence,
most of the cysteine residues and glycosylation sites, as well as other
blocks throughout the sequence. We interpret these conserved regions as
"framework" and nonconserved regions as "hypervariable," following the
terminology used to describe analogous regions in the IgG supergene family.
The low level of overall homology forms the basis of a general method for
isolating S-allele-specific cDNAs. Allele-specific antibodies can be
generated using synthetic peptides corresponding to one of the variable
regions. When applied to sections of the pistil, these antibodies label the
intercellular matrix in the stigma and transmitting tissue of the style and
the cell walls in the epidermis of the placenta. Hindlll digestion of
genomic DNA generates a characteristic pattern of S-gene fragments for each
genotype. These restriction fragment length polymorphisms can be used to
assign S-genotype to progeny arising from breeding experiments.
