Iron (Fe) is required for plant health, but it can also be toxic when present in excess. Therefore, Fe levels must be tightly controlled. The Arabidopsis thaliana E3 ligase BRUTUS (BTS) is involved in the negative regulation of the Fe deficiency response and we show here that the two A. thaliana BTS paralogs, BTS LIKE1 (BTSL1) and BTS LIKE2 (BTSL2) encode proteins that act redundantly as negative regulators of the Fe deficiency response. Loss of both of these E3 ligases enhances tolerance to Fe deficiency. We further generated a triple mutant with loss of both BTS paralogs and a partial loss of BTS expression that exhibits even greater tolerance to Fe-deficient conditions and increased Fe accumulation without any resulting Fe toxicity effects. Finally, we identified a mutant carrying a novel missense mutation of BTS that exhibits an Fe deficiency response in the root when grown under both Fe-deficient and Fe-sufficient conditions, leading to Fe toxicity when plants are grown under Fe-sufficient conditions.
We thank Brett Lahner and Elana Yakubov for performing the ICP-MS analysis and plant growth and harvesting, respectively, for the screen of EMS mutagenized plants. In memoriam, we thank John Danku for all the ICP-MS analyses included in this manuscript. Microarray analysis was carried out at the Geisel School of Medicine in the Genomics Shared Resource, which was established by equipment grants from the NIH and NSF and is supported in part by a Cancer Center Core Grant (P30CA023108) from the National Cancer Institute. We thank Amanda Socha for help with RNA extraction for microarray analysis and Carol Ringelberg for her help with microarray data analysis. We thank Suzana Car for her help with SXRF experiments at NSLS. We thank Sue Wirick and William Rao for their help at X26A and Ryan Tappero for his help at X27A. X26A is supported by the Department of Energy (DOE) – Geosciences (DE-FG02-92ER14244 to The University of Chicago – CARS). Use of the NSLS was supported by DOE under Contract No. DE-AC02-98CH10886. X27A is supported in part by the U.S. Department of Energy – Geosciences (DE-FG02-92ER14244 to The University of Chicago – CARS) and Brookhaven National Laboratory—Department of Environmental Sciences. Use of the NSLS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. We thank Sam Webb and Benjamin Kocar for their help at Beamline 2-3 at SSRL. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of NIGMS or NIH. We thank Suna Kim and Louisa Howard for the help with preparing leaf sections for Fig. 4E. We thank Tony Lanzirotti for his help at APS. Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. We thank Martin DeJonge and Daryl Howard for their help at XFM. This research was undertaken on the XFM beamline at the Australian Synchrotron, Victoria, Australia. This work was supported by grants to M. L. G. from the US National Science Foundation (DBI 0701119, IOS-0919941), the US National Institutes of Health (R01GM078536), the US Department of Energy (DE-FG-2-06ER15809), and the US National Institute of Environmental Health Sciences (P42 ES007373) and an NSF Plant Genome grant (DBI 0701119) to D. E. S. and M. L. G. M. N. H. was supported by a National Science Foundation Graduate Research Fellowship, a Nell Mondy Fellowship from Sigma Delta Epsilon-Graduate Women in Science, and a Dartmouth Graduate Alumni Research Award.