Characterization of molecules of the signal recognition and signal transduction phases of the self-incompatibility response in Brassica

To seed, or not to seed: that is the question. A simple one for Brassica, but still daunting to our attention. Sexual propagation: 'Tis a consummation devoutly to be wished, But, to seed, perchance to inbreed! Aye, there's the rub. What entities roam in thy mortal coil O! Pistil And what mechanisms hath thou employ to assure the proper union? Of these mysteries, I can only dimly perceive Molecular participants be known, their interactions still deceive.; The self-incompatibility (SI) response of Brassica entails a cell-cell communication event between pollen grain and stigma epidermal cell which culminates in the rejection of genetically related pollen by the stigma.; The S-locus glycoprotein (SLG) and S receptor kinase (SRK) are two S-locus-encoded proteins that are thought to be required for the SI response. Evidence presented here demonstrates both SLG and SRK to be stigma-specific proteins and SRK to be plasma membrane-targeted. In addition, the SLG population is heterogeneous: only some of the SLG glycoforms are capable of membrane association, and this subset is further distinguished by the presence of SLG oligomers. Analysis of mutant Brassica strains with abnormal SLG structure or expression revealed a lack of detectable levels of SRK protein in these plants although they possess normal levels of SRK transcript. Co-expression of SLG also specifically prevented aggregation of SRK produced in transgenic tobacco plants. The evidence suggests functional interaction between SLG and SRK and has implications on the role of SLG in the SI response as well as on the stability of transmembrane receptor proteins in general.; One of the characteristics of the SI response is the inhibition of incompatible pollen hydration. Analysis of self-compatible mutant Brassica plants had previously led to the isolation of the MIP-MOD (Major Intrinsic Protein-like MOD-locus associated) gene in wild type plants. Characterization of the MIP-MOD promoter region demonstrates its activity in the stigma papillar cells and the protein exhibits measurable water transport activity when expressed in Xenopus oocytes. The data support a role for the MIP-MOD protein in stigma cell hydrodynamics.