Pollen-pistil Interactions in the Genus Nicotiana

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McClure 9604645 Pollen-pistil interactions provide an important avenue for controlling plant reproduction. The factors controlling intraspecific and interspecific pollen recognition in the genus Nicotiana provide an excellent system for exploring these interactions. A great deal is known about S-RNase mediated intraspecific pollen recognition in self-incompatible Nicotiana alata. Furthermore, the interspecific crossing relationships between N. alata and its self-compatible relatives have been well described. Both types of pollen recognition clearly entail interactions between the pollen and the pistil. This research project uses biochemical and molecular biological tools to understand the molecular details of these interactions. In the previous funding period, cloned S-RNase genes from N. alata were expressed in transgenic plants to examine their role in controlling pollination. The key results were: 1) that S-RNases control the specificity of intraspecific pollination, 2) that recognition information is diffusely encoded in the S-RNase molecule, 3) that at least three genetically distinct mechanisms contribute to controlling interspecific pollination between N. alata and its self-compatible relatives, and 4) that S-RNase was implicated in interspecific pollen recognition and rejection. These results are important because they imply that S-RNase helps to define a window of genetic relatedness for compatible pollination. It has a role in rejecting self-pollen, and thus prevents inbreeding. It also has a role in rejecting interspecific pollen, and so acts to prevent very wide crosses. The major goals in this new proposal are: 1) to identify and characterize non-SRNase factors that contribute to pollen recognition, and 2) to examine the specificity of RNase dependent interspecific pollen rejection. One putative factor has already been identified by differential cDNA cloning. This new sequence will be characterized using immunological and transgenic plant methods. The cDNA cloning appr oach will be extended to identify further non-S-RNase factors related to pollen recognition. The specificity of interspecific pollen recognition will be addressed by comparing the pollination behavior of transgenic plants expressing a bacterial RNase with plants expressing S-RNase or recognition defective S-RNase. By understanding the natural mechanisms that control intraspecific and interspecific pollen recognition in the genus Nicotiana, these studies may contribute to efforts to artificially manipulate the breeding behavior of economically important plants.