Genetic analysis of the breakdown of self-incompatibility in Lycopersicon peruvianum
In the first part of the thesis, experiments are described where self-compatible tetraploids of L. peruvianum were isolated from tissue culture and the expression and inheritance of their S-related proteins was explored. The S-related protein profiles of styles of self-compatible tetraploids were indistinguishable from the diploid self-incompatible explant source based on SDS-PAGE. Progenies obtained from self-fertilization of two tetraploids were all found to be self-compatible. Cloned cDNA sequences of the S-related proteins were used to determine the inheritance at the locus in these progenies through Southern hybridization. The allelic ratio consistent with the predicted ratio obtained if only the pollen bearing two different alleles was successful in achieving fertilization. This work demonstrates that the observed self-compatibility in the tetraploids was due to failure of recognition of heterogenic pollen by the style, while the expression and activity of the S-related stylar proteins remained unaffected.
In the second part of the thesis, periclinal chimeras between the SI L. peruvianum (P) and the SC L. esculentum (E) were utilized to analyze the relative influence of apical cell layers as they relate to SI and Unilateral incompatibility (UI). Irrespective of the expression of S-proteins in the chimeral styles, the chimeras were compatible with P component indicating that there was failure of recognition of the "self" pollen (the chimeras and the P component are genetically similar at the S-locus). The breakdown of SI was not related to the RNase activity of the S-proteins which was intact in all chimeras. Therefore S-proteins are not sufficient to maintain the SI response. Since the response was lost if either of the two layers (L1 and L2) was composed of E component, we conclude that both L1 and L2 are required for the SI phenotype. On the other hand, UI response was maintained in all the chimeras in which the L1 or L2 layer was P. This seems to suggest that SI and UI responses are developmentally unrelated in these chimeras.
0479: Plant propagation