The genus Ipomoea (Convolvulaceae) has a sporophytic self-incompatibility s
ystem that is under the genetic control of a single multiallelic S-locus. S
elf-incompatibility reactions occur on the stigma surface at an early stage
after pollination, and result in the complete arrest of pollen germination
such that no seed is set. In a genetic analysis of 224 plants of diploid I
. trifida, collected from six native populations in Central America, we ide
ntified 49 different S-alleles that showed a linear dominance-recessive hie
rarchy. We also obtained a spontaneous self-compatible mutant and showed th
at this self-compatibility trait is due to mutation at the S-locus. To inve
stigate the molecular basis of sporophytic self-incompatibility in Ipomoea,
we analysed stigma proteins and mRNAs extracted from several different S-g
enotypes, using two-dimensional gel electrophoresis (2D-PAGE) and AFLP-base
d mRNA fingerprinting (AMF), respectively. From the 2D-PAGE analyses, S-loc
us-linked stigma proteins (SSPs) were identified. The amino acid sequences
of these proteins have a high homology to non-metallo short-chain alcohol d
ehydrogenases reported in several plant species. The SSP gene was mapped at
a distance of 1.2 cM from the S-locus. In the AMF analysis, we obtained a
clone homologous to the Brassica SRK, which showed no genetic linkage to th
e S-locus of Ipomoea. This suggests that the sporophytic self-incompatibili
ty system of Ipomoea is mediated through a different molecular mechanism to
that of Brassica. (C) 2000 Annals of Botany Company.