Faculty Sponsor

Bethany Karlin Zolman

Final Abstract for URS Program

Auxins are important hormones in plants that regulate growth and development. Disruptions in the auxin biosynthesis pathway result in morphological changes in phenotypes in the model plant Arabidopsis thaliana, including differences in root and leaf formation. Mutations in the Tryptophan Aminotransferase of Arabidopsis (TAA1) and YUCCA (YUC4) genes interfere with the plant's ability to synthesize Indole-3-acetic acid (IAA), the primary auxin involved in plant development. IBR1 and IBR3 act in the multistep conversion of indole-3-butyric acid (IBA) to IAA. ILL2, IAR3, and ILR1 hydrolyze IAA-amino acid conjugates into free IAA. The goal of our study was to determine the phenotypic effects of combination mutations disrupting these genes on plant growth and development.

Mutant lines with disruptions in auxin pathways were crossed to generate combination lines. Genotyping of segregating plant lines was performed via polymerase chain reaction (PCR) and gel electrophoresis to identify homozygous mutations in genes of interest. For this study, we used wild-type Arabidopsis (Columbia), parental lines, and double and quadruple-mutant combinations of the various genes. To determine the effects of these mutations and their combinations on plant growth and development, we focused on phenotypes associated with auxins such as root elongation, lateral root formation, hypocotyl elongation, and germination. The results of these assays demonstrate how the studied genes impact auxin-response pathways. By examining phenotypic data in wild-type and mutant plants we are able to determine the relationship between pathways in auxin-responsive growth. Because these genes play a key role in the growth and development of crop species as well, studying their effects on auxin-associated pathways in Arabidopsis may be informative for agricultural settings.

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