About the importance of mitochondrial complex I and associated gamma carbonic anhydrases for plant development, metabolism and the proteome

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Life without complex I: proteome analyses of an Arabidopsis mutant lacking the mitochondrial NADH dehydrogenase complex

The mitochondrial NADH dehydrogenase complex (complex I) is of particular importance for the respiratory chain in mitochondria. It is the major electron entry site for the mitochondrial electron transport chain (mETC) and therefore of great significance for mitochondrial ATP generation. We recently described an Arabidopsis thaliana double-mutant lacking the genes encoding the carbonic anhydrases CA1 and CA2, which both form part of a plant-specific 'carbonic anhydrase domain' of mitochondrial complex I. The mutant lacks complex I completely. Here we report extended analyses for systematically characterizing the proteome of the ca1ca2 mutant. Using various proteomic tools, we show that lack of complex I causes reorganization of the cellular respiration system. Reduced electron entry into the respiratory chain at the first segment of the mETC leads to induction of complexes II and IV as well as alternative oxidase. Increased electron entry at later segments of the mETC requires an increase in oxidation of organic substrates. This is reflected by higher abundance of proteins involved in glycolysis, the tricarboxylic acid cycle and branched-chain amino acid catabolism. Proteins involved in the light reaction of photosynthesis, the Calvin cycle, tetrapyrrole biosynthesis, and photorespiration are clearly reduced, contributing to the significant delay in growth and development of the double-mutant. Finally, enzymes involved in defense against reactive oxygen species and stress symptoms are much induced. These together with previously reported insights into the function of plant complex I, which were obtained by analysing other complex I mutants, are integrated in order to comprehensively describe 'life without complex I'.DFG/1186/Br1829/10–

Co-expression and regulation of photorespiratory genes in Arabidopsis thaliana: A bioinformatic approach

Laxa M, Fromm S. Co-expression and regulation of photorespiratory genes in Arabidopsis thaliana: A bioinformatic approach. CURRENT PLANT BIOLOGY. 2018;14:2-18.Being a pathway tightly linked to photosynthesis, photorespiration is regulated by light, but also by both nutrients and metabolites on transcriptional level. However, only little is known about the signals and how they are integrated on promoter level to coordinate the whole pathway. Using a bioinformatic approach we analyzed the co-expression patterns of photorespiratory genes, the predicted cis-regulatory elements in their 5' upstream regions and the existence of introns in their 5'UTRs. We found that there are groups of photorespiratory genes that are strongly co-expressed among each other. The analysis showed a high co-expression between photorespiration and ammonia re-fixation. However, a strong co-regulation between two genes, like GDCH1 and GDCH2, did not necessarily mean that these genes share common cis-element in their 5' upstream regions. TATA-box, MYB1AT, and MYB4 binding site motifs occurred in 16 out of 20 genes. Furthermore, photorespiratory genes are subjected to alternative splicing. We discuss the presence of cis-elements in the context of both stress responses and development. A genome wide analysis of Arabidopsis 5'UTRs revealed that 5'UTRs introns are overrepresented in photorespiratory genes. Promoter:gusA studies indicated that photorespiratory gene expression is also regulated by intron-mediated enhancement (IME). As already shown for glutamate: glyoxylate aminotransferase, transcript abundance of serine: glyoxylate aminotransferase was affected by IME on mRNA level. IME of gene expression of glycolate oxidase was shown to act on translational level