D. Charlesworth et al., Population-level studies of multiallelic self-incompatibility loci, with particular reference to Brassicaceae, ANN BOTANY, 85, 2000, pp. 227-239
Here we review some of the unsolved problems in understanding plant self-in
compatibility and attempt to show how a population genetics approach is int
egral to many interesting questions, including some of the problems involve
d in making inferences about which parts of the sequences of the known gene
s are involved in recognition functions. We describe preliminary results fr
om work on a species in the Brassica family, Arabidopsis (formerly Arabis)
lyrata. Our data indicate that this species has sporophytic self-incompatib
ility, with extensive dominance/recessivity of alleles. We have not yet att
empted to estimate allele numbers in samples from natural populations, but
there must be many alleles, since unrelated plants are usually cross-compat
ible. Using primers based on Brassica SLG and SRK sequences, we have amplif
ied several S-domain loci from A. lyrata genomic DNA and estimate that at l
east seven such loci are present. Using plants from geographically separate
d populations, we find that sequence diversity differs greatly from locus t
o locus. One set of sequences, representing one locus or at most a few loci
, shows linkage with incompatibility groups segregating within several inde
pendent families, consistent with this set of sequences representing allele
s of a self-incompatibility gene. However, further work is needed to test w
hether these sequences represent more than a single locus and whether expre
ssion patterns of these sequences are consistent with their having a role i
n self-incompatibility. (C) 2000 Annals of Botany Company.