Mitochondrial ABC Transporter ATM3 Is Essential for Cytosolic Iron-Sulfur Cluster Assembly.

The mitochondrial ATP-binding cassette transporter ATM3 has been studied in Arabidopsis. Its function, however, is poorly understood in other model plant species. This study reports that the ATM3 is required for cytosolic iron-sulfur cluster assembly and is essential for meristem maintenance in rice (Oryza sativa). The loss of function of OsATM3 is lethal in rice at the four-leaf stage. In the osatm3 T-DNA insertion mutant, the fourth leaf fails to develop and the lateral roots are short. Cytosolic iron-sulfur protein activities were significantly reduced in both osatm3 and RNA interference transgenic lines. The expression profiles of many iron metabolism genes were altered in the osatm3 and RNA interference lines. Glutathione metabolism was impaired and reactive oxygen species, particularly superoxide, accumulated in osatm3 Promoter-β-glucuronidase staining of the transgenic line indicated that OsATM3 is highly expressed in lateral root primordia, root tip meristem zones, and shoot apical meristem regions. The average cell size was significantly greater in osatm3 than in the wild type. Massive cell death occurred in the osatm3 root tip meristem zone. Quantitative RT-PCR revealed transcriptional reprogramming of the genes in the osatm3 and RNAi lines involved in DNA repair and cell cycle arrest. Our results suggest that the mitochondrial ATM3 is essential for iron homeostasis in rice.