Genotype and phenotype of Nicotiana alata x Nicotina rastroensis
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Gametophytic self-incompability (SI) is a process which enables plants to prevent inbreeding depression by rejecting self-pollen and pollen from closely related individuals. S-specific pollen rejection is controlled on a multi-allelic locus, the S-locus. If the S-allele of the haploid pollen matches either of the diploid pistil S-alleles, pollen tube growth is inhibited. The product of the S-locus is the active ribonuclease, S-RNase. We set out to test whether putative SC10 S-RNase growth from Nicotiana rastroensis truly segregates as an allele of the S-locus. We used a hybrid of Nicotiana alata and N. rastroensis for our study. The N. alata parent was homozygous for the S105 S-allele and the N. rastroensis parent had an SC10 and another unknown S-allele (Sx). Our experiment was to find out the genotype of the hybrids, and test the plants for rejection of SC10 pollen. We emasculated and pollinated flowers with SA2, S105, and SC10 pollen from N. alata. S-RNase expression leading to a pollen rejection phenotype was determined by fruit set. SDS-PAGE and western blot analysis with specific S-RNase antibodies was used to determine the genotype of the hybrids. The result expected was 50% of the plants have S105/SC10, and 50% have S105 and the unknown Sx, but we found that 75% contained SC10 + 25% had Sx. We saw that N. rastroensis SC10 S-RNase rejects SC10 pollen and accepts S105 pollen. Thus, we observed allele specific pollen rejection from the SC10 allele.