Honors Theses and Capstones

Date of Award

Spring 2020

Project Type

Senior Honors Thesis

College or School

COLSA

Department

Biochemistry, Molecular and Cellular Biology

Program or Major

Biochemistry

Degree Name

Bachelor of Science

First Advisor

Estelle Hrabak

Abstract

Protein Phosphatase 2A (PP2A) is a ubiquitous enzyme in eukaryotes that regulates a large array of cellular signaling processes. PP2A is composed of three subunits: catalytic C subunit, regulatory B subunit, and scaffolding/regulatory A subunit. In Arabidopsis thaliana, the A subunit has three isoforms - A1, A2, and A3 - that are highly conserved at the protein level, indicating that these proteins may be functionally interchangeable. In comparison to wildtype plants, seedlings with a mutation in the A1 gene have roots with obvious root cell file rotation or twisting under conditions of moderate salt stress. Twisted root cells result in a characteristic root curling phenotype when seedlings are grown on the surface of vertically-oriented agar plates. Mutations in the A2 and A3 genes do not result in any observable root phenotype, even though all three A subunit isoforms are expressed in roots. To test the hypothesis that differences in expression may be responsible for mutant phenotype variation, hybrid genes were constructed containing promoters from one subunit and coding regions of a different subunit, then transformed into a1mutant Arabidopsis to test for complementation. These tests showed that a1 mutants transformed with transgenes containing A1 or A3 promoters, regardless of coding region, had their mutant phenotype corrected, while the phenotypes of a1 mutants transformed with a2 promoters were only partially corrected. This supports the hypothesis that a deficit in the total A subunit pool, rather than subunit specificity, is a major contributor to the a1 mutant phenotype.

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