Genetic and molecular analyses of the S-locus in wild potato Solanum chacoense

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Self-incompatibility (SI) is one of the most widespread evolutionary devices used by flowering plants to promote gene exchange within a given species and avoid inbreeding.  In Solanaceous plants like Solanum chacoense the pistillar determinant to SI is an extremely polymorphic stylar extracellular S-RNase. The pollen determinant to SI has been identified as an F-box family member (SLF or S-locus F-box). It has been proposed that in compatible crosses,ubiquitin-mediated S-RNase degradation takes place. This, however, has not been unambiguously demonstrated. Indeed, it appears that the biochemistry and physiology underlying pollen rejection is a far more complex than previously suspected.We use genetics, molecular biology and plant tissue culture to address basic questions about SI. These include: 1) How do pollen tubes discriminate between self and non self S-RNases? 2) Apart from the S-RNase, what other components are required for the SI reaction? 3) What is the role of the conserved glycosylation site present in the C2 region of all solanaceous S-RNases? 4) Why are multiple F-box genes present at the S-locus and what is their function? 5) How do the pollen and pistillar determinants coevolve to maintain SI?OBJECTIVES  1) Cloning and characterization of the pollen-S F-box gene and other F-box genes present at the S-locus of our genotypes. 2) We will develop a pollen transformation system involving highly regenerable genotypes of appropriate S-allele constitution and a pollen-specific promotor. These constructs in both sense and antisense orientation should help in identifying the pollen-S F-box, and other F-box genes. 3) We will produce by site-directed mutagenesis an S11-RNase without glycosylation sites. We predict that plants expressing such transgene will reject all types of pollen.SIGNIFICANCE Additional knowledge on how the SI system works and evolve should open the way to exploit SI in production of hybrid seeds, fruit breeding, etc.