Al-induced Programmed Cell Death Research Articles

Mutator-like transposable element 9A interacts with metacaspase 1 and modulates the incidence of Al-induced programmed cell death in peanut.

The toxicity of aluminum (Al) in acidic soil inhibits plant root development and reduces crop yields. In the plant response to Al toxicity, the initiation of programmed cell death (PCD) appears to be an important mechanism for the elimination of Al-damaged cells to ensure plant survival. In a previous study, the type I metacaspase AhMC1 was found to regulate the Al stress response and to be essential for Al-induced PCD. However, the mechanism by which AhMC1 is altered in the peanut response to Al stress remained unclear. Here, we show that a nuclear protein, mutator-like transposable element 9A (AhMULE9A), directly interacts with AhMC1 in vitro and in vivo. This interaction occurs in the nucleus in peanut and is weakened during Al stress. Furthermore, a conserved C2HC zinc finger domain of AhMULE9A (residues 735-751) was shown to be required for its interaction with AhMC1. Overexpression of AhMULE9A in Arabidopsis and peanut strongly inhibited root growth with a loss of root cell viability under Al treatment. Conversely, knock down of AhMULE9A in peanut significantly reduced Al uptake and Al inhibition of root growth, and alleviated the occurrence of typical hallmarks of Al-induced PCD. These findings provide novel insight into the regulation of Al-induced PCD.

Identification and functional characterization of REGULATORY PARTICLE NON-ATPASE 1a-like (AhRPN1a-like) in peanuts during aluminum-induced programmed cell death

The toxicity of aluminum (Al) in acidic soil is a prevalent problem and causes reduced crop yields. In the plant response to Al toxicity, programmed cell death (PCD) appears to be one of the important mechanisms. However, the regulation of Al-induced PCD remains poorly understood. Here, we found that an uncharacterized protein REGULATORY PARTICLE NON-ATPASE 1a-like in peanut (AhRPN1a-like), located in the nucleus and cytoplasm, directly interacted with type I metacaspase in peanut (AhMC1). The overexpression of AhRPN1a-like in Arabidopsis strongly enhanced Al inhibition of root growth with a loss of root tip cell viability. Furthermore, in response to Al treatment, the VIGS knockdown line of AhRPN1a-like in peanut displayed decreased transcription of AhMC1, increased root growth, reduced Al-induced PCD and decreased 26S proteasomal activity. Taken together, these findings demonstrated that AhRPN1a-like interacted directly with AhMC1, and promotes the occurrence of Al-induced PCD via the 26S proteasome pathway, thereby reducing Al-resistance.

Lipid peroxide-derived short-chain aldehydes promote programmed cell death in wheat roots under aluminum stress.

Lipid peroxidation is a primary event in plant roots exposed to aluminum (Al) toxicity, which leads to the formation of reactive aldehydes. Current evidence demonstrates that the resultant aldehydes are integrated components of cellular damage in plants. Here, we investigated the roles of aldehydes in mediating Al-induced damage, particularly cell death, using two wheat genotypes with different Al resistances. Aluminum treatment significantly induced cell death, which was accompanied by decreased root activity and cell length. Al-induced cell death displayed granular nuclei and internucleosomal fragmentation of nuclear DNA, suggesting these cells underwent programmed cell death (PCD). During this process, caspase-3-like protease activity was extensively enhanced and showed a significant difference between these two wheat genotypes. Further experiments showed that Al-induced cell death was positively correlated with aldehydes levels. Al-induced representative diagnostic markers for PCD, such as TUNEL-positive nuclei and DNA fragmentation, were further enhanced by the aldehyde donor (E)-2-hexenal, but significantly suppressed by the aldehyde scavenger carnosine. As the crucial executioner of Al-induced PCD, the activity of caspase-3-like protease was further enhanced by (E)-2-hexenal but inhibited by carnosine in wheat roots. These results suggest that reactive aldehydes sourced from lipid peroxidation mediate Al-initiated PCD probably through activating caspase-3-like protease in wheat roots.

Circadian Rhythm Regulates Reactive Oxygen Species Production and Inhibits Al-Induced Programmed Cell Death in Peanut.

Peanut is among the most important oil crops in the world. In the southern part of China, peanut is highly produced; however, the arable land is acidic. In acidic soils, aluminum (Al) inhibits plant growth and development by changing the properties of the cell wall and causing the disorder of the intracellular metabolic process. Circadian rhythm is an internal mechanism that occurs about every 24 h and enables plants to maintain internal biological processes with a daily cycle. To investigate the effect of photoperiod and Al stress on the Al-induced programmed cell death (PCD), two peanut varieties were treated with 100 μM AlCl3 under three photoperiodic conditions (8/16, SD; 12/12, ND; 16/8 h, LD). The results show that Al toxicity was higher in ZH2 than in 99-1507 and higher under LD than under SD. Root length decreased by 30, 37.5, and 50% in ZH2 and decreased by 26.08, 34.78, and 47.82% in 99-1507 under SD, ND, and LD, respectively, under Al stress. Photoperiod and Al induced cell death and ROS production. MDA content, PME activity, and LOX activity increased under SD, ND, and LD, respectively, under Al stress both in ZH2 and 99-1507. APX, SOD, CAT, and POD activities were higher under SD, ND, and LD, respectively. Al stress increased the level of AhLHY expression under SD and ND but decreased it under LD in both ZH2 and 99-1507. Contrastingly, AhSTS expression levels increased exponentially and were higher under SD, LD, and ND, respectively, under Al stress. Our results will be a useful platform to research PCD induced by Al and gain new insights into the genetic manipulation of the circadian clock for plant stress response.

Integration of Small RNA and Degradome Sequencing Reveals the Regulatory Network of Al-Induced Programmed Cell Death in Peanut.

Peanut is one of the most important oil crops in the world. In China, the peanut is highly produced in its southern part, in which the arable land is dominated by acid soil. At present, miRNAs have been identified in stress response, but their roles and mechanisms are not clear, and no miRNA studies have been found related to aluminum (Al)-induced programmed cell death (PCD). In the present study, transcriptomics, sRNAs, and degradome analysis in the root tips of two peanut cultivars ZH2 (Al-sensitive, S) and 99-1507 (Al-tolerant, T) were carried out. Here, we generated a comprehensive resource focused on identifying key regulatory miRNA-target circuits that regulate PCD under Al stress. Through deep sequencing, 2284 miRNAs were identified and 147 miRNAs were differentially expressed under Al stress. Furthermore, 19237 target genes of 749 miRNAs were validated by degradome sequencing. GO and KEGG analyses of differential miRNA targets showed that the pathways of synthesis and degradation of ketone bodies, citrate cycle (TCA cycle), and peroxisome were responded to Al stress. The combined analysis of the degradome data sets revealed 89 miRNA-mRNA interactions that may regulate PCD under Al stress. Ubiquitination may be involved in Al-induced PCD in peanut. The regulatory networks were constructed based on the differentially expressed miRNAs and their targets related to PCD. Our results will provide a useful platform to research on PCD induced by Al and new insights into the genetic engineering for plant stress response.

Glucose-6-phosphate dehydrogenase and abscisic acid mediate programmed cell death induced by aluminum toxicity in soybean root tips

Programmed cell death (PCD) induced by aluminum (Al) is considered an important reason of Al phytotoxicity. However, the underlying mechanism of how Al induces PCD remains largely unknown in plants. The roles of glucose-6-phosphate dehydrogenase (G6PDH) and abscisic acid (ABA) in regulating Al-induced PCD were investigated in soybean roots. Al treatment increased G6PDH activity, while inhibition of G6PDH activity alleviated PCD occurrence and reactive oxygen species (ROS) accumulation under Al stress. Overexpression of cytosolic G6PDH1 enhanced G6PDH activity, thus promoting ROS production and cell death under Al exposure. Inhibition of NADPH oxidase activity mitigated ROS generation and cell death under Al stress. Further investigation demonstrated that G6PDH positively regulated the activity of NADPH oxidase under Al treatment using pharmacological and transgenic approach. Furthermore, Al stress increased ABA production, while inhibition of ABA biosynthesis alleviated PCD occurrence and ROS accumulation under Al stress. Interestingly, ABA upregulated G6PDH1 expression and G6PDH activity under Al stress. These results suggest that G6PDH mediates Al-induced PCD occurrence through the activation of NADPH oxidase-dependent ROS production, and ABA acts upstream of G6PDH in this process. This study will provide novel clues for the improvement of Al phytotoxicity in acidic soils.

Nitric oxide-mediated alternative pathway alleviates aluminum-induced programmed cell death in soybean root tips

Alternative pathway (AP) plays essential roles in plant adaptation to environmental stress. However, the exact role of AP in response to aluminum (Al) toxicity remains elusive. We here provide solid evidences that the activated AP capacity in root tips of soybean alleviated Al toxicity. Furthermore, inhibition of AP by pharmacological or transgenic approach aggravated Al-induced programmed cell death (PCD) occurrence mediated through reactive oxygen species (ROS)-dependent mitochondrial pathway. Our results also demonstrated that nitric oxide (NO) plays a negative role in PCD occurrence caused by Al in soybean root tips. Interestingly, the alleviating effect of NO on Al-induced PCD could be blocked by AP inhibition. Further investigation showed that NO mediates the induction of AP resulting from the upregulation of AOX expression and pyruvate content in Al-treated root tips of soybean. Taken together, our results clearly suggest that AP participates in the alleviation of Al toxicity and also plays a critical role in the alleviating effect of NO on Al-induced PCD occurrence, which will open up new avenues for the improvement of plant growth in acidic soils.

S-nitrosated proteomic analysis reveals the regulatory roles of protein S-nitrosation and S-nitrosoglutathione reductase during Al-induced PCD in peanut root tips

Nitric oxide-mediated S-nitrosation through S-nitrosoglutathione reductase (GSNOR) plays important roles in cellular processes and signaling of plants; however, the regulatory mechanism of programmed cell death (PCD) by S-nitrosation remains unclear. In this study, the S-nitrosated proteomic and functions of GSNOR during Al-induced PCD in peanut were investigated. Al stress induced an increase of S-nitrosothiol (SNO) content and GSNOR activity in Al-induced PCD. There was significant positive correlation between SNO content and hydrogen peroxide content. The S-nitrosated proteomic analysis identified 402 S-nitrosated proteins containing 551 S-nitrosated sites during Al-induced PCD in the root tips of peanut. These S-nitrosated proteins were involved in regulation of various biological processes including energy metabolism, maintenance of cell wall function and organic acid secretion. Among them, 128 S-nitrosated proteins were up-regulated and one was down-regulated after Al stress. Experiments with recombinant AhGSNOR revealed that activity of the enzyme was inhibited by its S-nitrosation, with a moderate decrease of 17.9 % after 100 μM GSNO incubation. These data provide novel insights to understanding the functional mechanism of NO-mediated S-nitrosation during plant PCD.

Metacaspase MC1 enhances aluminum-induced programmed cell death of root tip cells in Peanut

Metacaspases are cysteine-dependent proteases, which play essential roles in programmed cell death (PCD), and caspase-3-like protease is the crucial executioner. However, its response mechanism to aluminum (Al)-induced PCD is still elusive. Here, the type I metacaspase gene in peanut (Arachis hypoganea L.), AhMC1, was cloned from the Al-sensitive cultivar ZH2. Physiological and biochemical methods, as well as gene expression analyses, were employed to explore its function in Al-induced PCD in peanut root tips. AhMC1 had a 1068-bp open reading frame, encoding a peptide of 355 amino acids, and the purified protein exhibited a high caspase-3-like protease activity. Its expression levels in different tissues of peanut varieties ZH2 and 99–1507 (Al-tolerant) varied under Al-stress conditions. The subcellular localization indicated that AhMC1 was transferred from mitochondria into the cytoplasm. Furthermore, overexpressing AhMC1 reduced the resistance to Al stress. Sense transgenic plants showed a low relative root growth rate, and reduced superoxide dismutase, peroxidase, and catalase activities, compared with wild-type and antisense transgenic plants under Al-stress conditions, but had a high root-cell death rate, and increased Al and maleic dialdehyde contents. The data suggest that metacaspase AhMC1 is a positive factor in Al-induced PCD in peanut root tips.

Nitric oxide acts as an antioxidant and inhibits programmed cell death induced by aluminum in the root tips of peanut (Arachis hypogaea L.)

Aluminum (Al) causes programmed cell death (PCD) in plants. Our previous studies have confirmed that nitric oxide (NO) inhibits Al-induced PCD in the root tips of peanut. However, the mechanism by which NO inhibits Al-induced PCD is unclear. Here the effects of NO on mitochondrial reactive oxygen species (ROS), malondialdehyde (MDA), activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), expression of alternative oxidase (AhAOX) and cytochrome oxidase (AhCOX) were investigated in peanut (Arachis hypogaea L.) root tips treated with Al. The results showed that Al stress induced rapid accumulation of H2O2 and MDA and increased the ratio of SOD/APX. The up-regulation of AhAOX and AhCOX expressions was not enough to inhibit PCD occurrence. Sodium nitroprusside (SNP, a NO donor) decreased the ratio of SOD/APX and eliminated excess H2O2 and MDA, thereby inhibiting Al-induced PCD in the root tips of peanut. The expression of AhAOX and AhCOX was significantly enhanced in Al-induced PCD treated with SNP. But cPTIO (a NO specific scavenger) supply had the opposite effect. Taken together, these results suggested that lipid peroxidation induced by higher levels of H2O2 was an important cause of Al-induced PCD. NO-mediated inhibition of Al-induced PCD was related to a significant elimination of H2O2 accumulation by decreasing the ratio of SOD/APX and up-regulating the expression of AhAOX and AhCOX.

Identification and validation of reference genes for real-time qPCR normalization during Al-induced programmed cell death in peanut

The reverse transcription quantitative real-time PCR (RT-qPCR) is becoming increasingly important for gene expression studies. However, the accuracy and reliability of RT-qPCR depend on normalizing expression to reference genes. In this study, ten candidate reference genes, including cyclophilin (CYP), elongation factor 1b (EF1b), α-tubulin (TUA5), β-tubulin (TUB4), ubiquitin10R (UBQ10R), 60S ribosomal RNA (60S), alcohol dehydrogenase (ADH3), metalloprotease (MTP), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and actin (ACT2) were evaluated for the stability of expression in three tissues of two peanut cultivars [Zhonghua 2(ZH2) and 99-1507] under Al stress by four statistical algorithms (geNorm, NormFinder, BestKeeper, and RefFinder). The results suggested that the top-ranked reference genes under Al-induced programmed cell death (PCD) in peanut were UBQ10R, EF1b and CYP, with the most suitable combination of reference genes being [UBQ10R+ACT2]. The UBQ10R exhibited the most stable expression in all samples, while TUB4 was the least stable gene. The relative expression of AhMC1 (the caspase-like protease family gene, which played a significant role in Al-induced PCD) showed that there was no significant difference with the best reference gene and the best gene combination in RT-qPCR normalization, but there was significant difference with the least stable gene TUB4 as reference gene. This is the first study to evaluate the stability of reference genes in peanut under Al-induced PCD, and the results will provide guidance to identify appropriate reference genes for further RT-qPCR analyses under Al stress in peanut.

Nitric oxide suppresses aluminum-induced programmed cell death in peanut (Arachis hypoganea L.) root tips by improving mitochondrial physiological properties

Aluminum (Al) stress alters nitric oxide (NO) and induces programmed cell death (PCD) in plants. Recent study has shown that NO inhibits Al-induced PCD. However, the mechanism of NO inhibiting Al-induced PCD has not been revealed yet. Here, we investigated the behavior of mitochondria during Al-induced PCD suppressed by NO in peanut. Seedlings of peanut was grown hydroponically in a controllable growth room. The mitochondrial physiological parameters were determined spectrophotometrically. The expression of AhANT and AhHsp70 was determined by quantitative RT-PCR. Al-induced cell death rapidly in peanut root tips is mitochondria-dependent PCD. There was a significantly negative relationship between PCD and mitochondrial NO/H2O2 level. Compared with Al treatment alone, the addition of NO donor sodium nitroprusside (SNP) increased the ratio of NO/H2O2, down-regulated AhANT expression and inhibited the opening of mitochondrial permeability transition pore (MPTP), up-regulated AhHsp70 expression and increased mitochondrial inner membrane potential (ΔΨm), reduced cytochrome c (Cyt c) release from mitochondria and caspase 3-like protease activity, while the effect of NO specific scavenger cPTIO supplement was opposite. NO suppresses Al-induce PCD in peanut root tips by improving mitochondrial physiological properties.

Nitric Oxide Inhibits Al-Induced Programmed Cell Death in Root Tips of Peanut (Arachis hypogaea L.) by Affecting Physiological Properties of Antioxidants Systems and Cell Wall.

It has been reported that nitric oxide (NO) is a negative regulator of aluminum (Al)-induced programmed cell death (PCD) in peanut root tips. However, the inhibiting mechanism of NO on Al-induced PCD is unclear. In order to investigate the mechanism by which NO inhibits Al-induced PCD, the effects of co-treatment Al with the exogenous NO donor or the NO-specific scavenger on peanut root tips, the physiological properties of antioxidants systems and cell wall (CW) in root tip cells of NO inhibiting Al-induced PCD were studied with two peanut cultivars. The results showed that Al exposure induced endogenous NO accumulation, and endogenous NO burst increased antioxidant enzyme activity in response to Al stress. The addition of NO donor sodium nitroprusside (SNP) relieved Al-induced root elongation inhibition, cell death and Al adsorption in CW, as well as oxidative damage and ROS accumulation. Furthermore, co-treatment with the exogenous NO donor decreased MDA content, LOX activity and pectin methylesterase (PME) activity, increased xyloglucan endotransglucosylase (XET) activity and relative expression of the xyloglucan endotransglucosylase/hydrolase (XTH-32) gene. Taken together, exogenous NO alleviated Al-induced PCD by inhibiting Al adsorption in CW, enhancing antioxidant defense and reducing peroxidation of membrane lipids, alleviating the inhibition of Al on root elongation by maintaining the extensibility of CW, decreasing PME activity, and increasing XET activity and relative XTH-32 expression of CW.

Nitric oxide inhibits aluminum-induced programmed cell death in peanut (Arachis hypoganea L.) root tips

It had been reported that Aluminum (Al) stress altered nitric oxide (NO) concentration and induced programmed cell death (PCD) in plants. However, the relationship between NO and PCD occurrence under Al stress is unclear. The results showed that cell death induced by Al was significant negative correlation with the inhibition of Al on root elongation growth in peanut. AlCl3 at 100μmolL−1 induced DNA ladder, chromatin condensation, typical apoptotic chromatin condensation staining with DAPI, apoptosis related gene Hrs203j expression and caspase3-like protease activation in peanut root tip cells, and showed that Al-induced cell death in peanut root tip cells was a typical PCD. Exogenous NO donor sodium nitroprusside (SNP) at 200μmolL−1 inhibited Al-induced PCD occurrence, but NO specific scavenger cPTIO aggravated PCD production. It suggests that NO is a negative regulator of Al-induced PCD in peanut root tips.

Caspase-like proteases regulate aluminum-induced programmed cell death in peanut

Recent evidence has proved that caspase protease activities are detected in both mammals and plants during programmed cell death (PCD). The characteristics and functions of caspase-like proteases play important roles in understanding the mechanisms of PCD in plants. In this work, we report firstly the involvement of caspase-like protease activities and effects in aluminum (Al) stress in two contrasting peanut genotypes. Caspase-like activities in the root tip cells of ‘Zhonghua 2’ (Al-sensitive) and ‘99-1507’ (Al-tolerant) were detected using synthetic caspase substrates during Al-triggered PCD. Caspase-1-, -2-, -3-, -4-, -5-, -6-, -8- and -9-like proteases were found in peanut root tip cells. VDQQDase (caspase-2-like) and WEHD (caspase-5-like) were the first detected in the plants, and almost all of the caspase-like proteases were activated during Al-induced PCD, especially caspase-3-like and caspase-1-like, which was higher in ‘Zhonghua 2’ than in ‘99-1507’. The highest activity levels of caspase-3- and caspase-1-like proteases occurred 8 and 4 h after 100 µM Al treatment, respectively. Compared with 100 µM AlCl3 treatment alone, specific caspase-3 protease inhibitor Ac-DEVD-CHO inhibited the increase of caspase-3-like protease activity, Al content, Hsr203j expression, cell death and DNA fragmentation, and the decrease in root growth induced by 100 µM AlCl3 treatment, but it was more obvious in ‘Zhonghua 2’ than in ‘99-1507’. In conclusion, there were different caspase-like proteases in root tips of peanut, and caspase-3-like protease was a crucial executioner in Al-induced PCD. Its effects in the ‘Zhonghua 2’ genotype were higher than in ‘99-1507’. An improved model of the mechanism of Al-induced PCD and Al tolerance differences in different genotypes is proposed.

Determination of aluminum induced programmed cell death characterized by DNA fragmentation in Gramineae species

Aluminum (Al) toxicity is one of the major abiotic stress factors that decreases crop yield in acidic soils. Al inhibits the root growth and development due to cellular toxicity including nucleus, chromosome and DNA alterations. Although some Al-induced programmed cell death (PCD) features were identified, there are limited comparative and time-dependent studies. The aim of this study is to compare the Al-induced time-dependent DNA fragmentation, the most widely evaluated criterion for PCD in six agronomic plant (maize, wheat, triticale, rye, barley and oat) roots concerning their Al tolerance. Roots were exposed to 100 μM AlCl3 solution (pH 4.5) for different times (½, 1, 2, 3, 4, 5, 6, 7, 8 h). All genomic DNA was isolated from control and AlCl3 treated roots. Isolated DNA samples were analyzed by electrophoretically and DNA fragmentation was observed in triticale, rye, barley and oat roots, but not in maize and wheat. The obtained DNA fragmentation shows that wheat and maize are more tolerant than triticale, rye, barley and oat in which the PCD is active as early as ½ h after Al induction. The results obtained can provide a better understanding into the Al induced PCD and Al tolerance in plants.

Aluminum induces rapidly mitochondria-dependent programmed cell death in Al-sensitive peanut root tips.

BackgroundAlthough many studies suggested that aluminum (Al) induced programmed cell death (PCD) in plants, the mechanism of Al-induced PCD and its effects in Al tolerance is limited. This study was to investigate the mechanism and type of Al induced PCD and the relationship between PCD and Al tolerance.ResultsIn this study, two genotypes of peanut 99-1507 (Al tolerant) and ZH2 (Al sensitive) were used to investigate Al-induced PCD. Peanut root growth inhibition induced by AlCl3 was concentration and time-dependent in two peanut varieties. AlCl3 at 100 μM could induce rapidly peanut root tip PCD involved in DNA cleavage, typical apoptotic chromatin condensation staining with DAPI, apoptosis related gene Hrs203j expression and cytochrome C (Cyt c) release from mitochondria to cytosol. Caspase3-like protease was activated by Al; it was higher in ZH2 than in 99-1507. Al increased the opening of mitochondrial permeability transition pore (MPTP), decreased inner membrane potential (ΔΨm) of mitochondria. Compared with the control, Al stress increased O2•- and H2O2 production in mitochondria. Reactive oxygen species (ROS) burst was produced at Al treatment for 4 h.ConclusionsAl-induced PCD is earlier and faster in Al-sensitive peanut cultivar than in Al-tolerant cultivar. There is a negative relationship between PCD and Al resistance. Mitochondria- dependence PCD was induced by Al and ROS was involved in this process. The mechanism can be explained by the model of acceleration of senescence under Al stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-014-0067-1) contains supplementary material, which is available to authorized users.

Overexpression of ALTERNATIVE OXIDASE1a alleviates mitochondria-dependent programmed cell death induced by aluminium phytotoxicity in Arabidopsis.

Alternative oxidase (AOX) is a terminal oxidase found in all plants, and functions to maintain the electron flux and reduce the production of reactive oxygen species (ROS). Our previous study demonstrated that aluminium (Al) treatment could induce increased expression of the AOX1a gene, but the mechanism of how AOX1a participates in the regulation of Al-induced programmed cell death (PCD) is still not clear. To investigate the possible mechanism, mitochondrial ROS production and the behaviour of mitochondria, as well as caspase-3-like activation were monitored under Al treatment in wild-type (WT), AOX1a-lacking (aox1a), and AOX1a-overexpressing (AOX1a-OE) Arabidopsis. Our results showed that Al treatment increased the expression of AOX1a at both the transcriptional and translational levels. Overexpression of AOX1a reduced mitochondrial ROS production by maintaining the mitochondrial electron flux, and alleviated subsequent mitochondrial dysfunction and caspase-3-like activation in Al-induced PCD. Moreover, it was found that a change in AOX1a level could influence the expression levels of downstream functional genes that play protective roles in Al-induced PCD. Experiments using mutants and inhibitors demonstrated that superoxide anion (O2 (-)) derived from mitochondria was involved in Al-induced upregulation of AOX1a gene expression. Taken together, these results indicated that overexpression of AOX1a alleviated Al-induced PCD by maintaining mitochondrial function and promoting the expression of protective functional genes, providing new insights into the signalling cascades that modulate the Al phytotoxicity mechanism.

Aluminum-induced programmed cell death promoted by AhSAG, a senescence-associated gene in Arachis hypoganea L.

Programmed cell death (PCD) is a foundational cellular process in plant development and elimination of damaged cells under environmental stresses. In this study, Al induced PCD in two peanut (Arachis hypoganea L.) cultivars Zhonghua 2 (Al-sensitive) and 99-1507 (Al-tolerant) using DNA ladder, TUNEL detection and electron microscopy. The concentration of Al-induced PCD was lower in Zhonghua 2 than in 99-1507. AhSAG, a senescence-associated gene was isolated from cDNA library of Al-stressed peanut with PCD. Open reading frame (ORF) of AhSAG was 474bp, encoding a SAG protein composed of 157 amino acids. Compared to the control and the antisense transgenic tobacco plants, the fast development and blossom of the sense transgenic plants happened to promote senescence. The ability of Al tolerance in sense transgenic tobacco was lower than in antisense transgenic tobacco according to root elongation and Al content analysis. The expression of AhSAG-GFP was higher in sense transgenic tobacco than in antisense transgenic tobacco. Altogether, these results indicated that there was a negative relationship between Al-induced PCD and Al-resistance in peanut, and the AhSAG could induce or promote the occurrence of PCD in plants

Mitochondrial pathway leading to programmed cell death induced by aluminum phytotoxicity in Arabidopsis

Recent studies have reported some apoptosis-like characters under Al treatment including nucleus morphology changes and appearance of nucleus fragmentation in plant cells. Our recent report has suggested that mitochondrial oxidative burst, mitochondrial swelling and mitochondrial transmembrane potential (MTP) disrupt play crucial roles in Al-induced caspase-3-like activation and programmed cell death (PCD). And Complex I and III might be the sources of Al-induced mitochondrial reactive oxygen species (ROS) through interaction between Al and iron-sulfur (Fe-S) protein. Our study contributed to the understanding of mitochondria-dependent cellular signaling cascade of plant biological responses in Al-induced PCD. However, the mitochondria-dependent mechanism in Al-induced PCD needs further improvement, and the roles of mitochondria functional proteins are still poorly understood compared with the study of signaling pathways involved in animal cell apoptosis. By using the fluorescence techniques and the Arabidopsis mesophyll protoplasts as a reference model, the subsequent researches have been carried out to obtain comprehensive understanding of Al-induced plant PCD.