Abstract
BackgroundThe tricarboxylic acid (TCA) cycle is crucial for cellular energy metabolism and carbon skeleton supply. However, the detailed functions of the maize TCA cycle genes remain unclear.ResultsIn this study, 91 TCA genes were identified in maize by a homology search, and they were distributed on 10 chromosomes and 1 contig. Phylogenetic results showed that almost all maize TCA genes could be classified into eight major clades according to their enzyme families. Sequence alignment revealed that several genes in the same subunit shared high protein sequence similarity. The results of cis-acting element analysis suggested that several TCA genes might be involved in signal transduction and plant growth. Expression profile analysis showed that many maize TCA cycle genes were expressed in specific tissues, and replicate genes always shared similar expression patterns. Moreover, qPCR analysis revealed that some TCA genes were highly expressed in the anthers at the microspore meiosis phase. In addition, we predicted the potential interaction networks among the maize TCA genes. Next, we cloned five TCA genes located on different TCA enzyme complexes, Zm00001d008244 (isocitrate dehydrogenase, IDH), Zm00001d017258 (succinyl-CoA synthetase, SCoAL), Zm00001d025258 (α-ketoglutarate dehydrogenase, αKGDH), Zm00001d027558 (aconitase, ACO) and Zm00001d044042 (malate dehydrogenase, MDH). Confocal observation showed that their protein products were mainly localized to the mitochondria; however, Zm00001d025258 and Zm00001d027558 were also distributed in the nucleus, and Zm00001d017258 and Zm00001d044042 were also located in other unknown positions in the cytoplasm. Through the bimolecular fluorescent complimentary (BiFC) method, it was determined that Zm00001d027558 and Zm00001d044042 could form homologous dimers, and both homologous dimers were mainly distributed in the mitochondria. However, no heterodimers were detected between these five genes. Finally, Arabidopsis lines overexpressing the above five genes were constructed, and those transgenic lines exhibited altered primary root length, salt tolerance, and fertility.ConclusionSequence compositions, duplication patterns, phylogenetic relationships, cis-elements, expression patterns, and interaction networks were investigated for all maize TCA cycle genes. Five maize TCA genes were overexpressed in Arabidopsis, and they could alter primary root length, salt tolerance, and fertility. In conclusion, our findings may help to reveal the molecular function of the TCA genes in maize.
Highlights
The tricarboxylic acid (TCA) cycle is crucial for cellular energy metabolism and carbon skeleton supply
Bioinformatics analysis of the maize TCA cycle genes To comprehensively analyse the functions of the maize TCA genes, 91 TCA cycle genes were identified in the maize genome through sequence similarity searching, and few genes with higher E-values than the threshold were included in this study (Fig. 1 and Additional file 2)
Four genes were identified for both citrate synthase (CSY) and malate dehydrogenase (MDH), and 13, 11 and 6 genes were identified for MDH, ACO, and succinyl-CoA synthetase (SCoAL), respectively
Summary
The tricarboxylic acid (TCA) cycle is crucial for cellular energy metabolism and carbon skeleton supply. The TCA cycle is ubiquitous in animals, plants and microbial cells and is crucial for cellular energy and carbon skeleton supply, especially for sugar catabolism, fat catabolism, and protein catabolism [1]. The TCA cycle consists of eight enzymes, citrate synthase (CSY), aconitase (ACO), isocitrate dehydrogenase (IDH), α-ketoglutarate dehydrogenase complex (αKGDHC), succinyl-CoA synthetase (SCoAL), succinate dehydrogenase (SDH), fumarase (FUM), and malate dehydrogenase (MDH). A series of studies on TCA mutants in tomato showed that fumarase, malate dehydrogenase, and ɑ-ketoglutarate dehydrogenase play key roles in regulating the metabolic level of the TCA cycle [2]. Most of the reactions of the TCA cycle are reversible, except for the synthesis of citric acid and succinyl-CoA [3, 4]. The reactions catalysed by SCoAL and SDH in the TCA cycle can only be carried out in mitochondria, while other reactions in the TCA cycle can be replaced by similar reactions in other subcellular compartments [2]
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