9808478 Stern Sporopollenin, often referred to as the most resistant biopolymer on earth, is an essential component of mature pollen grains. Sporopollenin is also found in the spore walls of non seed plants, and in the resting cells of diverse microorganisms. Despite the importance of this apparently ancient compound, the routes of synthesis, secretion, and assembly of sporopollenin remain unknown. The zygospore wall of Chlamydomonas monoica contains sporopollenin and the availability of zygospore mutants of this unicellular alga suggests development of C. monoica as a model for the study of sporopollenin biosynthesis and function. The composition of the zygospore wall will be analyzed using differential fixation and staining followed by fluorescence or transmission electron microscopy and by electrophoresis of proteins solubilized during wall morphogenesis in wildtype and mutant strains. A nuclear transformation procedure will be developed and wildtype alleles of genes responsible for zygospore defects will be isolated by their ability to complement mutant phenotypes, using an indexed cosmid library for transformation. Alternatively, insertional maturation mutants will be generated by nuclear transformation and the molecular tag will then be used to clone the defective gene. The expression of genes cloned by these approaches will be compared in wildtype and maturation mutants.
