Modular structure of complex II: An evolutionary perspective

Succinate dehydrogenases (SDHs) and fumarate reductases (FRDs) catalyse the interconversion of succinate and fumarate, a reaction highly conserved in all domains of life. The current classification of SDH/FRDs is based on the structure of the membrane anchor subunits and their cofactors. It is, however, unknown whether this classification would hold in the context of evolution. In this work, a large-scale comparative genomic analysis of complex II addresses the questions of its taxonomic distribution and phylogeny. Our findings report that for types C, D, and F, structural classification and phylogeny go hand in hand, while for types A, B and E the situation is more complex, highlighting the possibility for their classification into subgroups. Based on these findings, we proposed a revised version of the evolutionary scenario for these enzymes in which a primordial soluble module, corresponding to the cytoplasmatic subunits, would give rise to the current diversity via several independent membrane anchor attachment events.

Phytochrome-mediated regulation of plant respiration and photorespiration

The expression of genes encoding various enzymes participating in photosynthetic and respiratory metabolism is regulated by light via the phytochrome system. While many photosynthetic, photorespiratory and some respiratory enzymes, such as the rotenone-insensitive NADH and NADPH dehydrogenases and the alternative oxidase, are stimulated by light, succinate dehydrogenase, subunits of the pyruvate dehydrogenase complex, cytochrome oxidase and fumarase are inhibited via the phytochrome mechanism. The effect of light, therefore, imposes limitations on the tricarboxylic acid cycle and on the mitochondrial electron transport coupled to ATP synthesis, while the non-coupled pathways become activated. Phytochrome-mediated regulation of gene expression also creates characteristic distribution patterns of photosynthetic, photorespiratory and respiratory enzymes across the leaf generating different populations of mitochondria, either enriched by glycine decarboxylase (in the upper part) or by succinate dehydrogenase (in the bottom part of the leaf).

Specific changes in total and mitochondrial proteomes are associated with higher levels of heterosis in maize hybrids

The phenomenon of hybrid vigor (heterosis) has long been harnessed by plant breeders to improve world food production. However, the changes that are essential for heterotic responses and the mechanisms responsible for heterosis remain undefined. Large increases in biomass and yield in high-heterosis hybrids suggest that alterations in bioenergetic processes may contribute to heterosis. Progeny from crosses between various inbred lines vary in the extent of vigor observed. Field-grown maize F₁ hybrids that consistently exhibited either low or high heterosis across a variety of environments were examined for changes in proteins that may be correlated with increased plant vigor and yield. Unpollinated ears at the time of flowering (ear shoots) were selected for the studies because they are metabolically active, rich in mitochondria, and the sizes of the ears are diagnostic of yield heterosis. Total protein and mitochondrial proteomes were compared among low- and higher-heterosis hybrids. Two-dimensional difference gel electrophoresis was used to identify allelic and/or isoform differences linked to heterosis. Identification of differentially regulated spots by mass spectrometry revealed proteins involved in stress responses as well as primary carbon and protein metabolism. Many of these proteins were identified in multiple spots, but analysis of their abundances by label-free mass spectrometry suggested that most of the expression differences were due to isoform variation rather than overall protein amount. Thus, our proteomics studies suggest that expression of specific alleles and/or post-translational modification of specific proteins correlate with higher levels of heterosis.