Differential expression of uncoupling mitochondrial protein and alternative oxidase in the plant response to stress Thais Resende Silva Figueira & Paulo Arruda Published online: 21 January 2011 # Springer Science+Business Media, LLC 2011 Abstract Different cell types, organs and tissues shape their mitochondrial proteome according to the cellular environment that is dictated by differentiation, develop- ment and metabolic status. Under each circumstance, members of multigenic families that encode mitochondrial proteins are differentially expressed to meet the mito- chondrial metabolic demand. However, the mitochondrial proteome may drastically change in response to stress conditions. Examples of the changes in mitochondrial protein expression caused by stress are represented by the energy-dissipating mitochondrial uncoupling protein (UCP) and alternative oxidase (AOx). UCP and AOx belong to multigenic families in plants, and their mem- bers, which are expressed in a time/tissue specific manner, respond differentially to stress conditions. In general, UCP and AOx are not expressed at the same levels concurrently in the same tissue, and the level of each protein varies in each stress condition. In addition, under non-stress conditions, UCP is expressed at much higher levels compared with AOx. The role of their differential expression in plant growth, development and response to stress is discussed. Keywords Plant . Mitochondria . UCP . AOx . Stress Introduction Plants possess at least two energy-dissipating systems in their mitochondria: one is comprised of uncoupling proteins (UCPs), and the other is comprised of alternative oxidases (AOxs). Both systems lead to a decrease in the efficiency of oxidative phosphorylation. AOx also leads to heat produc- tion in certain tissues of thermogenic plants, whereas UCP, although it is involved in heat production in the brown adipose tissue (BAT) of mammals (Nicholls and Rial 1999), has not been associated with heat production in plants (Jarmuszkiewicz et al. 2001). UCP and AOx are present concurrently in the mitochondria of green tomato fruit, but these proteins do not work simultaneously because free fatty acids block the activity of AOx while activating UCP (Sluse and Jarmuszkiewicz 2000). Recently, investigations into the sequenced plant genomes and EST collections have allowed the identification and characterization of the gene families that encode UCP and AOx (Hourton-Cabassa et al. 2004; Borecky et al. 2006). UCP and AOx are ubiquitous in plants and could have various physiological roles including heat production and protection against oxygen free radicals (Ito-Inaba et al. 2009). UCP may also play a role in regulating the energy metabolism in mitochondria to cope with the excessive production of reactive oxygen species (Brandalise et al. 2003a; Considine et al. 2003). AOx could work as a valve in situations that lead to increases in reducing power and phosphate potential in the cell (Jarmuszkiewicz et al. 2001). Thus, the two energy- dissipating pathways seem to complement the absence of one another to meet the physiological demand of a particular cell/tissue or to respond to particular changes imposed by stress. In this review, we focus on the role of the UCP and AOx gene families in the plant response to stress. T. R. S. Figueira : P. Arruda (*) Centro de Biologia Molecular e Engenharia Genética, Universidade Estadual de Campinas (UNICAMP), 13083-970 Campinas, SP, Brazil e-mail: parruda@unicamp.br P. Arruda Departamento de Genética e Evolução, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), 13083-970 Campinas, SP, Brazil J Bioenerg Biomembr (2011) 43:67–70 DOI 10.1007/s10863-011-9333-z