Minisymposium 17: Mineral Nutrition

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Abs # M1702: Natural ionomic variation in Arabidopsis identifies an E3 ubiquitin ligase involved in regulating shoot Mo.

Presenter:	Baxter, Ivan R       Contact Presenter
Authors	Baxter, Ivan R (A)   Lahner, Brett  (A)   Rus, Ana  (A)   Hoekenga, Owen  (B)   Yakubova, Elena  (A)   Harper, Jeffrey  (C)   Guerinot, Mary Lou  (D)   Salt, David E (A)
Affiliations:	(A): Purdue University (B): Boyce Thompson Institute for Plant Research, Cornell University (C): University of Nevada, Reno (D): Dartmouth University

The natural ecotypes (accessions) of Arabidopsis thaliana provide a rich source of genetic diversity that leads to potentially adaptive phenotypic differences. To identify genes responsible for variation in mineral ion homeostasis among accessions, we measured the levels of Li, B, Na, Mg, P, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo and Cd, in the shoots and seeds of 12 different accessions. Each one showed significant differences in the shoot accumulation of more than one element when compared with the reference accession col-0, and 9 of the 12 accession showed at least one significant difference in the seed elemental profile. Interestingly, there was very little correspondence between the elemental differences in the shoots and seeds of the same accession. Using this natural variation in the shoot ionome we have previously identified HKT1 and FPT2 as controlling Na and Co/Ni accumulation, respectively. Here we present evidence for the involvement of a novel RING-type E3 ubiquitin ligase in the regulation of Mo in shoots of Arabidopsis. Our initial screen of 12 Arabidopsis accessions revealed that compared to col-0, Ler-2 has low shoot and seed Mo, and cvi-1 has high shoot Mo. Analysis of cvi-1 x Ler-2 & col-4 x Ler recombinant inbred line populations revealed quantitative trait loci (QTL) for multiple elements including Mo. The Mo QTL for both low shoot and seed Mo were found to colocalize on chromosome 2. Using a combination of QTL and microarray based bulk segregant analysis (BSA), coupled with transcript profiling, we were able to identify several candidates for the loci controlling low Mo in Ler. An analysis of insertional mutants in these candidate genes allowed us to identify a novel RING-type E3 ubiquitin ligase as being responsible for the phenotype. Sequencing of the gene in low Mo accumulating accessions identified two candidate single nuclotide polymorphisms which change amino acids in the IBD domain of the protein. The T-DNA insertion line showed significant segregation distortion and the heterozygote plants accumulated significantly less Mo than wild-type plants.