Analysis of the Rice Mitochondrial Carrier Family Reveals Anaerobic Accumulation of a Basic Amino Acid Carrier Involved in Arginine Metabolism during Seed Germination  

Given the substantial changes in mitochondrial gene expression, the mitochondrial proteome, and respiratory function during rice (Oryza sativa) germination under anaerobic and aerobic conditions, we have attempted to identify changes in mitochondrial membrane transport capacity during these processes. We have assembled a preliminary rice mitochondrial carrier gene family of 50 members, defined its orthology to carriers of known function, and observed significant changes in microarray expression data for these rice genes during germination under aerobic and anaerobic conditions and across rice development. To determine if these transcript changes reflect alteration of the carrier profile itself and to determine which members of the family encode the major mitochondrial carrier proteins, we analyzed mitochondrial integral membrane protein preparations using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and peptide mass spectrometry, identifying seven distinct carrier proteins. We have used mass spectrometry-based quantitative approaches to compare the abundance of these carriers between mitochondria from dry seeds and those from aerobic- or anaerobic-germinated seeds. We highlight an anaerobic-enhanced basic amino acid carrier and show concomitant increases in mitochondrial arginase and the abundance of arginine and ornithine in anaerobic-germinated seeds, consistent with an anaerobic role of this mitochondria carrier. The potential role of this carrier in facilitating mitochondrial involvement in arginine metabolism and the plant urea cycle during the growth of rice coleoptiles and early seed nitrate assimilation under anaerobic conditions are discussed.