Role of differential expression of <Emphasis Type="Italic">sdh1-1</Emphasis> and <Emphasis Type="Italic">sdh1-2</Emphasis> genes in alteration of isoenzyme composition of succinate dehydrogenase in germinating maize seeds

A probable mechanism of alteration of the isoenzyme composition of succinate dehydrogenase (SDH) due to differential expression of genes encoding subunit A was considered. The alteration of SDH activity during maize seed germination was investigated, and its maximal activity on day 4-5 of germination was found. The alteration of the sdh1-1 and sdh1-2 gene expression level during maize seed germination was evaluated using the quantitative polymerase chain reaction method. The presence of four forms of the studied enzymes, providing multiple SDH functions was found in maize inflorescence using electrophoresis in polyacrylamide gel.     

Three different genes encode the iron-sulfur subunit of succinate dehydrogenase in Arabidopsis thaliana

The iron-sulfur protein is an essential component of mitochondrial complex II (succinate dehydrogenase, SDH), which is a functional enzyme of both the citric acid cycle and the respiratory electron transport chain. This protein is encoded by a single-copy nuclear gene in mammals and fungi and by a mitochondrial gene in Rhodophyta and the protist Reclinomonas americana. In Arabidopsis thaliana, the homologous protein is now found to be encoded by three nuclear genes. Two genes (sdh2-1 andsdh2-2) likely arose from a relatively recent duplication event since they have similar structures, encode nearly identical proteins and show similar expression patterns. Both genes are interrupted by a single intron located at a conserved position. Expression was detected in all tissues analysed, with the highest steady-state mRNA levels found in flowers and inflorescences. In contrast, the third gene (sdh2-3) is interrupted by 4 introns, is expressed at a low level, and encodes a SDH2-3 protein which is only 67% similar to SDH2-1 and SDH2-2 and has a different N-terminal presequence. Interestingly, the proteins encoded by these three genes are probably functional because they are highly conserved compared with their homologues in other organisms. These proteins contain the cysteine motifs involved in binding the three iron-sulfur clusters essential for electron transport. Furthermore, the three polypeptides are found to be imported into isolated plant mitochondria.     

Succinate dehydrogenase in Arabidopsis thaliana is regulated by light via phytochrome A

The effect of light on succinate dehydrogenase (SDH) activity and mRNA content was studied in Arabidopsis thaliana plants. The transition from darkness to light caused a short transient increase in the SDH activity followed by a decrease to a half of the original activity. The white or red light were found to be down-regulating factors for the mRNA content of the sdh1-2 and sdh2-3 genes and SDH catalytic activity both in A. thaliana wild-type plants and in the mutant deficient in the phytochrome B gene, but not in the mutant deficient in the phytochrome A gene, while the far-red light of 730 nm reversed the red light effect. It is concluded that phytochrome A participates in the regulation of mitochondrial respiration through effect on SDH expression.     

The role of calcium cations in the mechanism of phytochrome-dependent regulation of the <Emphasis Type="Italic">sdh1-2</Emphasis> gene expression and succinate dehydrogenase activity in maize leaves

The regulation of succinate dehydrogenase (SDH) activity and its gene expression by the phytochrome system has been demonstrated: red light (660 nm) reduces the SDH activity and the level of expression of the sdh1-2 gene. At the same time, the content of calcium cations in the nuclear fraction increases; it seems to be one of the mechanisms of phytochrome signal transduction in plant cells. Far-red light (730 nm) had opposite effects, i.e., increased SDH activity and the level of expression of the sdh1-2 gene. The data suggest that the SDH activity can be regulated at the level of expression in the green leaves of Zea mays by the phytochrome system with the involvement of calcium ions as a signal transduction messenger.     

Regulation of succinate dehydrogenase (sdhCDAB) operon expression in Escherichia coli in response to carbon supply and anaerobiosis: role of ArcA and Fnr

Succinate dehydrogenase (SDH) of Escherichia coli, the sole membrane-bound enzyme of the tricarboxylic acid cycle, participates in the aerobic electron-transport pathway to generate energy via oxidative phosphorylation reactions. Previous studies have established that succinate dehydrogenase (SDiH) synthesis is elevated by aerobiosis and supressed during growth with glucose. To examine how the sdhCDAB genes that encode SDH are regulated by changes in the environment, sdh–lacZ fusions were constructed and analysed in vivo following cell growth under a variety of alternative culture conditions. Expression of sdh–lacZ was highest under aerobic conditions and was decreased 10-foid in the absence of oxygen. The fnr and arcA gene products are required for this oxygen control and each acts to repress sdhC–lacZ expression. Expression of sdh–lacZ also varied 10- to 14-foid depending on the type of carbon substrate used or the medium richness. This control was shown to be independent of the crp and fruR gene products, and indicates that some other regulatory element exists in the ceil to adjust SDH enzyme levels accordingly. Iron and haem availability affected sdhC–lacZ expression by two- to threefold. Lastly, fold. Lastly, sdhC–lacZ expression was shown to vary with the cell growth rate during aerobic and anaerobic conditions.     

云南栘[木衣]MADS-box基因家族鉴定与表达分析

MADS-box基因家族是一类重要的转录因子家族,在调控植物的生长发育、信号传导等过程中发挥着重要作用。为研究云南栘[木衣][Docynia delavayi(Franch.)Schneid.]MADS-box基因家族的特征及其在种子不同萌发时期的表达情况,本研究以云南栘[木衣]不同萌发时期的种苗为材料,在转录组测序的基础上利用生物信息学方法从云南栘[木衣]转录组数据库中筛选MADS-box转录因子,分析其理化性质、蛋白保守基序、系统进化及表达模式,并采用实时荧光定量PCR(quantitative real-time polymerase chain reaction,qRT-PCR)实验验证云南栘[木衣]MADS-box基因家族成员在种子不同萌发时期的表达情况。在云南栘[木衣]转录组数据中共鉴定出81个MADS-box转录因子,其编码的氨基酸序列分子量分布范围在6211.34–173512.77 Da之间,等电点介于5.21−10.97之间。系统进化分析显示,81个云南栘[木衣]MADS-box基因可分为15个亚组,其中DdMADS27、DdMADS42、DdMADS45、DdMADS46、DdMADS53、DdMADS61、DdMADS76、DdMADS77和DdMADS79可能参与对云南栘[木衣]胚珠的发育调控。结合云南栘[木衣]种子转录组数据与qRT-PCR实验分析发现,DdMADS25和DdMADS42可能参与调控种子发育,DdMADS37和DdMADS38可能对种子休眠有负调控作用。前人报道中MIKC*亚组多参与调控花器官发育,本研究首次发现MIKC*亚组的转录因子在种子萌发前期具有较高表达量,由此推测MIKC*亚组在种子萌发过程中起到调控作用。为验证该推测准确性,挑选了MIKC*亚组的DdMADS60和DdMADS75进行qRT-PCR实验,实验结果与转录组测序的表达趋势一致。本研究可为进一步从分子进化角度研究云南栘[木衣]MADS-box基因家族的生物学功能提供参考。     

Evolution of a secondary metabolic pathway from primary metabolism: shikimate and quinate biosynthesis in plants

The shikimate pathway synthesizes aromatic amino acids essential for protein biosynthesis. Shikimate dehydrogenase (SDH) is a central enzyme of this primary metabolic pathway, producing shikimate. The structurally similar quinate is a secondary metabolite synthesized by quinate dehydrogenase (QDH). SDH and QDH belong to the same gene family, which diverged into two phylogenetic clades after a defining gene duplication just prior to the angiosperm/gymnosperm split. Non‐seed plants that diverged before this duplication harbour only a single gene of this family. Extant representatives from the chlorophytes (Chlamydomonas reinhardtii), bryophytes (Physcomitrella patens) and lycophytes (Selaginella moellendorfii) encoded almost exclusively SDH activity in vitro. A reconstructed ancestral sequence representing the node just prior to the gene duplication also encoded SDH activity. Quinate dehydrogenase activity was gained only in seed plants following gene duplication. Quinate dehydrogenases of gymnosperms, represented here by Pinus taeda, may be reminiscent of an evolutionary intermediate since they encode equal SDH and QDH activities. The second copy in P. taeda maintained specificity for shikimate similar to the activity found in the angiosperm SDH sister clade. The codon for a tyrosine residue within the active site displayed a signature of positive selection at the node defining the QDH clade, where it changed to a glycine. Replacing the tyrosine with a glycine in a highly shikimate‐specific angiosperm SDH was sufficient to gain some QDH function. Thus, very few mutations were necessary to facilitate the evolution of QDH genes.     

山梨糖脱氢酶在脱氮副球菌中的表达

目的:在脱氮副球菌PD1222中表达山梨糖脱氢酶(SDH)。方法:从质粒pMD-18T上复制氨苄西林抗性基因Ampr,从酮古龙酸菌中复制SDH基因sdh,先后酶切连接到pIND4质粒上,构建pIND4-Ampr-sdh穿梭质粒;再把pIND4-Ampr-sdh电转入大肠杆菌S17-1λpir作为供体菌,脱氮副球菌PD1222为受体菌进行双亲本接合转移;挑取壮观霉素和氨苄西林双抗平板上的接合子进行培养,菌液PCR复筛接合子,测序鉴定,通过DCIP法和非变性聚丙烯酰胺凝胶电泳法检测阳性克隆的SDH活性。结果:构建的质粒pIND4-Ampr-sdh成功转入脱氮副球菌PD1222中,SDH获得表达并检测到其蛋白活性。结论:实现了SDH在脱氮副球菌中的表达,为在脱氮副球菌中研究SDH的下游电子传递链奠定了基础。     

The four subunits of mitochondrial respiratory complex II are encoded by multiple nuclear genes and targeted to mitochondria in Arabidopsis thaliana

Mitochondrial respiratory complex II contains four subunits: a flavoprotein (SDH1), an iron-sulphur subunit (SDH2) and two membrane anchor subunits (SDH3 and SDH4). We have found that in Arabidopsis thaliana SDH1 and SDH3 are encoded by two, and SDH4 by one nuclear genes, respectively. All these encoded polypeptides are found to be imported into isolated plant mitochondria. While both SDH1 proteins are highly conserved when compared to their counterparts in other organisms, SDH3 and SDH4 share little similarity with non-plant homologues. Expression of SDH1-1, SDH3 and SDH4 genes was detected in all tissues analysed, with the highest steady-state mRNA levels found in flowers and inflorescences. In contrast, the second SDH1 gene (SDH1-2) is expressed at a low level.