Genetic characterization and molecular cloning of genes involved in kernel development in Zea mays
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This dissertation describes the genetic and molecular characterization of maize genes that are required for kernel development. Maize stocks in which the Robertson's Mutator (Mu) transposable element system are especially active were used to generate 75 mutations affecting kernel development. Sixty-four kernel mutations were located to chromosome arm, and 17 were placed to more precise locations on the maize genetic map. Viability tests of kernels homozygous for defective kernel (dek) mutations revealed numerous pleiotropic effects on plants obtained from mutant kernels. Fifteen putative Mutator-induced mutations tested negative for allelism to any known gene required for kernel development, and thus represent previously undescribed maize loci. Among the 75 mutations studied, 13 cases of allelism were identified, including a series of ten new alleles of the Et1 locus. Extensive phenotypic diversity was noted in this series of et1 alleles, including endosperm, seedling, and embryo phenotypes previously undescribed for et1 mutations;Because these kernel mutations are derived from Robertson's Mutator stocks and many are probably tagged with a Mu-element insertion, the corresponding loci theoretically are accessible to molecular cloning via transposon tagging. Therefore, these mutations are likely to be a valuable resource for biochemical and molecular investigations of kernel development in maize. Towards the goal of characterizing genes required for maize kernel development at the molecular level, a specific restriction fragment of genomic DNA containing the transposon Mu1 and tightly linked to the defective kernel mutation emp2 was cloned into a phage lambda vector. Evidence indicating that the Mu1-tagged genomic fragment was derived from the emp2 allele includes an analysis of wild type siblings of the emp2/Emp2 prototype plant that do not contain a Mu-element insertion in the genomic fragment that was cloned, and detecting of mRNA from the cloned region of the genome in developing kernels;A similar approach was used to obtain a Mu1-homologous clone tightly-linked to the dsc1 mutation that identifies a mRNA that accumulates early in kernel development. The dsc1-linked clone contains sequences highly homologous to the upstream non-coding region of a maize gene expressed specifically in developing endosperm.