Causes and Consequences of an Age Dependent Breakdown in Self-Incompatibility in Campanula rapunculoides

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9527739 STEPHENSON Fertilization in plants is the culmination of a series of interactions between the pollen grain and the female part of a flower (the pistil). Each flowering plant in the world today is here because the pollen of each of its paternal ancesters succeeded in fertilizing an egg that produced a seed. An understanding of pollen tube growth and the interactions of growing pollen tubes with the pistil are fundamental to the plant sciences, just as the ability to manipulate the growth of pollen has profound implications for the applied plant science and biotechnology. One of the most interesting and potentially useful pollen-pistil interactions is self-incompatibility (SI). SI is a genetic system that allows a plant to recognize and reject self pollen while permitting the growth of cross pollen. This mechanism allows plants to avoid the deleterious effects of inbreeding. Recently, we have found that the flowers of Campanula plants are self-incompatible when they first open but, as the flowers become older, they permit growth and fertilization by self pollen. The research funded in this award will identify the genetic causes of this breakdown in SI over time; it will examine the molecular basis for the breakdown in SI; it will determine how the breakdown in SI leads to different levels of inbreeding under different environmental circumstances; and it will use DNA sequence information to begin to look at the evolution of SI. Results will allow tests of competing hypotheses in three active and highly debated areas of basic plant biology: the population biology of pollen performance, the evolution and maintenance of mixed mating systems (partial selfing), and the evolution of SI. Findings should assist in the development of cost-saving and time-saving methodology for the production of inbred lines needed by commercial plant breeding programs.