Self-incompatibility (SI) is widespread in the angiosperms, but identifying the biochemical components of SI mechanisms has proven to be difficult in most lineages. Coffea (coffee; Rubiaceae) is a genus of old-world tropical understory trees in which the vast majority of diploid species utilize a mechanism of gametophytic self-incompatibility (GSI). The S-RNase GSI system was one of the first S...

The products of the S-locus expressed in female tissues of Nicotiana alata are ribonucleases (S-RNases). The arrest of growth of incompatible pollen tubes in styles may result from entry of the S-RNase into the pollen tube and degradation of pollen tube RNA. We investigated the action of isolated S-RNases on pollen tubes grown in vitro and found that S-RNase is taken up by the pollen without su...

S-RNase-based gametophytic self-incompatibility (GSI) has evolved once before the split of the Asteridae and Rosidae. This conclusion is based on the phylogenetic history of the S-RNase that determines pistil specificity. In Rosaceae, molecular characterizations of Prunus species, and species from the tribe Pyreae (i.e., Malus, Pyrus, Sorbus) revealed different numbers of genes determining S-po...

The S-peptide and S-protein fragments of ribonuclease S (RNase S, no EC no. assigned) have been immobilized onto separate Sepharose gels via a "leash" of polycytidylic acid substrate. Each of these gels releases its RNase fragment when treated with the complementary enzyme fragment or with RNase A (EC 3.1.27.5), and the released fragments recombine to give RNase S activity. Thus this system pro...

The amino-terminal 20 amino acids are required for microinjected ribonuclease A (RNase A) to be taken up by lysosomes and degraded at an enhanced rate during serum withdrawal. We used water-soluble carbodiimides to covalently attach the RNase S-peptide (residues 1-20) to [3H]RNase S-protein (residues 21-124) at unspecified locations. We then measured catabolism of the [3H]S-protein-S-peptide co...

As a core factor in S-RNase-based gametophytic self-incompatibility (GSI), the SCF (SKP1-Cullin1-F-box-Rbx1) complex (including pollen determinant SLF, S-locus-F-box) functions as an E3 ubiquitin ligase on non-self S-RNase. The SCF complex is formed by SKP1 bridging between SLF, CUL1, and Rbx1; however, it is not known whether an SCF complex lacking SKP1 can mediate the ubiquitination of S-RNas...

Gametophytic self-incompatibility (GSI) allows plants to block fertilization by haploid pollen whose S-allele constitution matches one of the two S-alleles in the diploid styles. GSI in Solanum chacoense requires a stylar S-RNase, first secreted from cells of the transmitting tract then imported into incompatible (self) pollen tubes. However, the molecular mechanisms allowing compatible pollen ...

S-heteroallelic pollen (HAP) grains are usually diploid and contain two different S-alleles. Curiously, HAP produced by tetraploids derived from self-incompatible diploids are typically self-compatible. The two different hypotheses previously advanced to explain the compatibility of HAP are the lack of pollen-S expression and the "competition effect" between two pollen-S gene products expressed...

Noncovalent protein-ligand complexes are readily detected by electrospray ionization mass spectrometry (ESI-MS). Ligand binding stoichiometry can be determined easily by the ESI-MS method. The ability to detect noncovalent protein-ligand complexes depends, however, on the stability of the complexes in the gas-phase environment. Solution binding affinities may or may not be accurate predictors o...

Self-incompatibility (SI) in flowering plants entails the inhibition of fertilization by pollen that express specificities in common with the pistil. In species of the Solanaceae, Rosaceae, and Scrophulariaceae, the inhibiting factor is an extracellular ribonuclease (S-RNase) secreted by stylar tissue. A distinct but as yet unknown gene (provisionally called pollen-S) appears to determine the s...