Poster: Mineral nutrition
Abs #
200: Identification of amino acid residues critical for post-translational regulation of the IRTI metal transporter by iron in Arabidopsis.
|
|
Presenter: |
Kerkeb, Loubna , loubna@biol.sc.edu |
Authors | Kerkeb, Loubna (A) Mukherjee, Indrani (A) Ash, Joshua (A) Connolly, Erin L (A) | | Affiliations: |
(A): Dept. of Biological Sciences, University of South Carolina
|
|
|
Although iron is an essential micronutrient, it is toxic if accumulated at high levels. Hence, iron uptake and sequestration are controlled by precise regulatory mechanisms. IRT1 (Iron Regulated Transporter) is the major high affinity iron transporter responsible for iron uptake from the soil in Arabidopsis; IRT1 belongs to the ZIP family of metal transporters. Previously, we showed that IRT1 is subject to post-transcriptional regulation; IRT1 protein accumulates only in iron-deficient roots of 35S-IRT1 plants. IRT1 contains an intracellular loop that may be critical for post-translational regulation by metals; of particular interest is a histidine motif (HGHGHGH) that is found in many ZIP family members. In addition, we targeted two intracellular loop lysine residues that could serve as attachment sites for ubiquitin. We constructed a set of mutants: IRT1H154Q, IRT1H156Q, IRT1H158Q, IRT1H160Q, IRT14HQ (quadruple his mutant), IRT1K146R, IRT1K171R and a double mutant (IRT1K146R,K171R). All mutants were able to rescue the iron- and zinc-limited growth defects of the fet3fet4 and zrt1zrt2 yeast strains, respectively. This result demonstrates that mutation of the his or lys residues does not eliminate the ability of IRT1 to transport iron or zinc. Each of the IRT1 variants and an IRT1intact construct were expressed in plants from the 35S promoter. Western analysis revealed that 35S-IRT1K146R,K171R plants accumulate IRT1 protein when grown on iron-sufficient and iron-deficient medium while 35S-IRT1 plants accumulate IRT1 protein only when grown on iron-deficient medium. 35S-IRT1K146RK171R plants also accumulate higher levels of metals than 35S-IRTI and WT. These findings suggest a role for ubiquitination in metal-induced removal of IRT1 from the plasma membrane.
