Department of Plant Sciences

Mitochondria utilize iron (Fe), but the proteins involved in mitochondrial Fe regulation have not been characterized in plants. We cloned and characterized a mitochondrial iron-regulated (MIR) gene that is involved in Fe homeostasis in rice. MIR expressed in tobacco BY-2 cells was localized to the mitochondria. MIR transcription was significantly increased in response to Fe deficiency in the roots and shoots. MIR is not homologous to any known protein, as no homologs were found in the rice or Arabidopsis genome databases, or in the EST database for other organisms. Growth in the MIR T-DNA knock-out rice mutant (mir) was significantly impaired compared with wild-type (WT) plants, under both Fe-sufficient and Fe-deficient conditions. Furthermore, Fe accumulation in shoots and roots of mir plants was more than twice that in WT plants, under both Fe-sufficient and Fe-deficient conditions. Despite the high accumulation of Fe in roots and shoots, Fe deficiency-inducible genes were expressed in mir plants, indicating that mir may not be able to utilize the Fe for physiological functions. These results suggest that MIR is a rice-specific mitochondrial protein that plays a significant role in Fe homeostasis.