Date of Award

8-9-2014

Document Type

Open Access Thesis

Department

Biological Sciences

First Advisor

Erin Connolly

Abstract

Iron (Fe) is the fourth most abundant element within the earth’s crust and is an essential micronutrient for plants and animals. Fe plays key roles in photosynthesis, respiration and chlorophyll biosynthesis in plants and in hemoglobin in animals. Like Fe, copper (Cu) is also an important micronutrient in plants and is needed for photosynthesis and respiration, especially in the important copper-containing protein plastocyanin. Copper also is important in scavenging reactive oxygen species and ethylene perception. The reduction of Fe3+ to Fe2+ at the root surface of Arabidopsis thaliana during times of Fe deficiency has been a well-characterized process; however, reduction of Cu2+ to Cu1+ at the root surface is less well understood. It is known that a member of the FRO family of Arabidopsis genes, FRO2, functions to reduce Fe3+ to Fe2+ prior to import, but a role for copper reduction in Cu uptake in response to Cu deficiency was not previously known. The work presented in this thesis describes the characterization of two additional members of the FRO family, FRO4 and FRO5, that have been shown to have high amino acid sequence similarity. FRO4 and FRO5 function in the reduction of Cu2+ to Cu1+ at the root surface. For the characterization of these two genes, we isolated a T-DNA knockout line of FRO4, fro4, which lacks full-length FRO4 transcript. In addition, we generated and characterized artificial microRNA knockdown lines for FRO5 and for both FRO4 and FRO5 (double knockdown line). Under copper deficiency, FRO4 and FRO5 are highly expressed in root and shoot tissue. Loss-of-function mutants show only basal levels of reductase activity under Cu deficiency and grow poorly on Cu deficient hydroponic media compared to their wild-type counterparts. Taken together, these data support the hypothesis that FRO4 and FRO5 are the principle copper reductases during Cu deficiency in Arabidopsis and function redundantly to reduce Cu2+ to Cu1+ as part of the high affinity Cu uptake system.

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Biology Commons

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