Date of Award


Document Type


Degree Name

Master of Science (MS)


Genetics and Biochemistry

Committee Chair/Advisor

Julia Frugoli

Committee Member

Haiying Liang

Committee Member

Hong Luo


Nodules in legumes allow the plant to form a symbiotic interaction with bacteria, providing access to the inert N2 in the atmosphere. The Autoregulation of Nodulation Pathway (AON), a negative regulatory feedback mechanism, is a long-distance signaling system which controls the nodule numbers formed on roots, helping the plant conserve energy by not hosting bacterial symbionts beyond those needed by the plant. A forward genetic screen of the EMS mutagenized supernodulating sunn-1 mutant, a weak allele of SUNN in Medicago truncatula, identified 6 lines of heritable suppressor mutants that reduced the nodulating phenotype from supernodulating to wild-type. We used genetic mapping approaches to identify gene areas that could contain the lesion responsible for one of these mutants, the sos204 (suppressor of sunn-1 204) mutant. Identification and rescue of this suppressor mutation would allow for the opportunity to study more about the genes involved in the AON pathway. Data from previous Whole Genome Sequencing analysis and mapping efforts revealed Chromosome 2 as a possible candidate linked to this mutation. We categorize the F2 progeny of a sunn-1 plant crossed to sunn-1 sos204 into three different phenotypes: supernodulating, intermediate and suppressed. Chi-square analysis on the observed F2 progeny shows that the numbers deviate from multiple combinations of Mendel’s law of inheritance assuming recessive genes, giving no clear information about the number of genes that are involved in this mutation. A clear, conclusive segregation pattern was not observed in the F2, however, genotyping the F2 reveals the possibility of multiple genes harboring the lesion for this mutant: two gene regions in chromosome 2, and one gene region in chromosome 8. Although the source for the mutation linked to the suppression phenotype could not be identified, I discuss alternate possibilities of what our results could infer and the reasons behind it, along with the challenges faced during the mapping process.

Available for download on Friday, May 31, 2024

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