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

Heat stress in plants: sensing, signalling, and ferroptosis

In the current context of global warming, high temperature events are becoming more frequent and intense in many places around the world. In this context, understanding how plants sense and respond to heat is essential to develop new tools to prevent plant damage and address global food security, as high temperature events are threatening agricultural sustainability. This review summarizes and integrates our current understanding underlying the cellular, physiological, biochemical, and molecular regulatory pathways triggered in plants under moderately high and extremely high temperature conditions. Given that extremely high temperatures can also trigger ferroptosis, the study of this cell death mechanism constitutes a strategic approach to understand how plants might overcome otherwise lethal temperature events.

Physiological basis of nano-silica deposition-related improvement in aluminum tolerance in pea (Pisum sativum)

Aluminum(Al) toxicity is a major constraint affecting crop growth in acidic soils across the globe. Excessive Al levels in such soils not only negatively affect crop growth but also have significant implications for human health. This study aimed to explore the feasibility of increasing tolerance to Al stress by creating biomineralization structures in plant roots by nano-silica, and to explore the physiological basis silicon-mediated alleviation of Al toxicity in plants. The polyethylenimine was used to induce nano-silica to form biomineralization structures on the surface of root tip and root border cells in pea (Pisum sativum) plants. The results showed that under Al stress conditions, the deposition of nano-silica on the cell wall of pea root border cells induced by polyethyleneimine effectively increased cell viability and reduced reactive oxygen species(ROS) production by 44%, thus slowing down the programmed cell death. Such deposition also resulted in more Al ions(Al3+) absorbed by the surface of the root tip, thus preventing Al3+ from entering the root tip and alleviating the toxic effects of Al on cell metabolism. It is concluded that polyethylenimine- induced nano-silica deposition on the cell wall endows pea root cells with Al tolerance, thus enhancing crop growth and reducing toxic Al load, contributing to food safety and human health.

AhASRK1, a peanut dual-specificity kinase that activates the Ca2+-ROS-MAPK signalling cascade to mediate programmed cell death induced by aluminium toxicity via ABA

Aluminium (Al)-induced programmed cell death (PCD) is thought to be a main cause of Al phytotoxicity. However, the underlying mechanism by which Al induces PCD in plants is unclear. In this study, we characterized the function of AhASRK1 (Aluminum Sensitive Receptor-like protein Kinase1), an Al-induced LRR-type receptor-like kinase gene. AhASRK1 was localized on the plasma membrane. A kinase assay of recombinant cytoplasmic domains of AhASRK1 revealed that this leucine-rich repeat-receptor-like protein kinase autophosphorylates both serine/threonine and tyrosine residues. The role of AhASRK1 in regulating Al-induced PCD was investigated in roots. Al treatment significantly inhibited root growth and promoted ROS production and cell death after AhASRK1 was overexpressed in Arabidopsis, whereas the knockdown of AhASRK1 in peanut increased Al tolerance. AhASRK1 overexpression resulted in increased accumulation of apical calcium ions (Ca2+) and increased MAPK signalling under Al treatment; however, the AhASRK1-knockdown peanut lines exhibited a decrease in the Ca2+ concentration under Al stress. Furthermore, inhibition of ABA biosynthesis mitigated PCD occurrence and ROS accumulation under Al stress, as did Al-induced Ca2+ and p MAPK signalling. These results suggest that AhASRK1 mediates the occurrence of PCD through the ABA pathway to mediate the accumulation of Ca2+ and the production of ROS, thereby activating MAPK signalling. Additionally, AhASRK1 overexpression promoted leaf senescence and induced the transcription of a multitude of ABA-related genes. This study provides new clues for improving the phytotoxicity of Al in acidic soils.

Cytoplasmic G6PDs modulate callus formation in Arabidopsis root explants through regulation of very-long-chain fatty acids accumulation

Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway, impacts cancer cell proliferation and plant stress responses. However, its role in plant cell dedifferentiation and callus formation is not well understood. This study explores the function of cytoplasmic G6PD isoforms in Arabidopsis pericycle cell reprogramming into callus by employing a suite of mutant analyses, qRT-PCR, and GC-MS. Our findings demonstrate that g6pd5/6 double mutants exhibit enhanced callus formation compared to wild-type and single mutants, implicating cytoplasmic G6PDs as negative regulators of callus development. The double mutant showed reduced NADPH levels and increased expression of very-long-chain fatty acid (VLCFA) biosynthesis genes and the VLCFA-downstream gene Aberrant Lateral Root Formation 4 (ALF4) on callus-inducing medium (CIM). Notably, VLCFA concentrations were decreased in g6pd5/6 mutants, and supplementation of VLCFA reduced callus area. Additionally, callus formation in the alf4/g6pd5/6 triple mutant aligned with wild-type, suggesting a redundant inhibitory function of G6PD5 and G6PD6 in the regulation of VLCFA accumulation and related signaling. Contrasting with their roles in cancer cell proliferation, our study unveils novel insights into the G6PD signaling pathway, highlighting its unique function in negatively regulating plant callus formation.

Functional characterisation of WRKY transcription factor CrWRKY48 involved in regulating seed abortion of Ponkan (Citrus reticulata)

Citrus fruits are one of the most important fruits in the world, and their seedless character is favored by consumers. WRKY is a plant-specific transcription factor family involved in all aspects of plant growth and development. However, the molecular mechanism of seedless fruit formation in citrus and the role of the WRKY gene family in seed abortion are still poorly understood. In this study, we identified 47 WRKY family genes in the citrus fruit Citrus reticulata and comprehensively characterized the WRKY gene family through gene structure and evolutionary relationships. The expression patterns and protein interaction networks of the WRKY gene family were analyzed based on citrus seed abortion transcriptome data, and several WRKY genes that may be involved in the seed abortion regulation were excavated. Furthermore, CrWRKY48 was verified to regulate seed abortion positively in Arabidopsis thaliana, and the rate of seed abortion caused by overexpression of CrWRKY48 reached 45.48%. Using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assays, DNA affinity purification sequencing and yeast-one-hybrid assays, we found that CrWRKY48 activated excessive programmed cell death by regulating the expression of programmed cell death-related genes such as SOBIR1. Our results show the potential regulation of the WRKY gene family for citrus seed abortion and provide novel insights into the role of CrWRKY48 in mediating citrus seed abortion by activating programmed cell death.

Reciprocal inhibition of autophagy and Botrytis cinerea-induced programmed cell death in 'Shine Muscat' grapes

Botrytis cinerea causes gray mold, decreasing the quality of table grapes. The berry response to B. cinerea infection was explored in present study, focusing on the relationship between presence of autophagy and programmed cell death (PCD). Results demonstrated B. cinerea infection decreased cell viability, triggering cell death, possibly resulting in PCD occurrence. It was further verified by increased terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive nuclei, heightened caspase 3-like and caspase 9-like protease activity, and elevated expression of metacaspase genes. Additionally, autophagy was indicated by the increased VvATG expression and autophagosome formation. Notably, the autophagy activator rapamycin reduced TUNEL-positive nuclei, whereas the autophagy inhibitor 3-methyladenine increased caspase 9-like protease activity. The PCD activator C2-ceramide inhibited autophagy, whereas the PCD inhibitor Acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) enhanced autophagy gene expression. Autophagy and B. cinerea-induced PCD in berry cells are reciprocally negatively regulated; and the rapamycin and Ac-DEVD-CHO could potentially maintain table grape edible quality.

TRX h2-PP2AC2 module serves as a convergence node for aluminum stress and leaf senescence signals, regulating cell death via ABA-mediated ROS pathway

ROS/redox signaling plays an important role in the regulation of signal transduction and acclimation pathways activated by multiple abiotic stresses and leaf senescence. However, the regulatory events that produce ROS under different stimuli are far from clear. Here, we report the elucidation of the molecular mechanism of an h type thioredoxin, AhTRX h2, positively regulates Al sensitivity and leaf senescence by promoting ROS. AhTRX h2 transcript levels increased greatly during both natural senescence and Al stress condition in peanut. Ectopic expression of AhTRX h2 in Arabidopsis conferred Al sensitivity as well as premature leaf senescence, manifested by multiple indices, including inhibiting root elongation, severe cell death, and accelerated expression of MC1 and CEX17. AhTRX h2 exhibited similar functions to AtTRX h2, as AhTRX h2 was able to restore the phenotypes of the AtTRX h2 defective mutant (trxh2-4) which showed Al tolerant and late senescence phenotypes. The knock down of AhTRX h2 markedly suppressed Al- and senescence-induced cell death in peanut. AhTRX h2 could recruit catalytic subunit of protein phosphatase 2A (PP2AC2) to form a stable complex. The interaction between AhTRX h2 and AtPP2AC2, as well as AhPP2AC2 and AtTRX h2 was also proved. Overexpression of AhPP2AC2 significantly enhanced Al sensitivity and leaf senescence in Arabidopsis. Protein stability assay revealed that AhTRX h2 was more stable during aging or aluminum stress. Moreover, PP2AC2 could greatly enhance the stability of AhTRX h2 in vivo. Consistent with these observations, overexpression of AhPP2AC2 effectively enhanced AhTRX h2-induced Al sensitivity and precocious leaf senescence. AhTRX h2 and AhPP2AC2 required ABA and ROS in response to cell death under Al stress and senescence, and it was evidence to suggest that ABA acted upstream of ROS in this process. Together, AhTRX h2 and AhPP2AC2 constitute a stable complex that promotes the accumulation of ABA and ROS, effectively regulate cell death. These findings suggest that TRX h2-PP2AC2-mediated pathway may be a widespread mechanism in regulating Al stress and leaf senescence.

Two Half-Size ATP-Binding Cassette Transporters Are Implicated in Aluminum Tolerance in Soybean

Aluminum (Al) toxicity severely restricts plant production in acidic soils. ATP-binding cassette (ABC) transporters participate in plant tolerance to various environmental stresses. However, ABC transporters implicated in soybean Al tolerance are still rare. Here, we functionally characterized two half-size ABC transporters (GmABCB48 and GmABCB52) in soybean. Expression analysis showed that GmABCB48 and GmABCB52 were induced only in the roots, especially in the root tips. Both GmABCB48 and GmABCB52 were localized at the plasma membrane. Overexpression of GmABCB48 or GmABCB52 in Arabidopsis reduced Al accumulation in roots and enhanced Al tolerance. However, expression of GmABCB48 or GmABCB52 in yeast cells did not affect Al uptake. Furthermore, transgenic lines expressing GmABCB48 or GmABCB52 had lower Al content in root cell walls than wild-type plants under Al stress. Further investigation showed that the Al content in cell wall fractions (pectin and hemicellulose 1) of transgenic lines was significantly lower than that of wild-type plants, which was coincident with the changes of pectin and hemicellulose 1 content under Al exposure. These results indicate that GmABCB48 and GmABCB52 confer Al tolerance by regulating the cell wall polysaccharides metabolism to reduce Al accumulation in roots.

Strigolactones alleviate AlCl3 stress by vacuolar compartmentalization and cell wall blocking in apple

Poor management and excess fertilization of apple (Malus domestica Borkh.) orchards are causing increasingly serious soil acidification, resulting in Al toxicity and direct poisoning of roots. Strigolactones (SLs) are reported to be involved in plant responses to abiotic stress, but their role and mechanism under AlCl3 stress remain unknown. Here, we found that applying 1 μm GR24 (an SL analoge) significantly alleviated AlCl3 stress of M26 apple rootstock, mainly by blocking the movement of Al through cell wall and by vacuolar compartmentalization of Al. RNA-seq analysis identified the core transcription factor gene MdWRKY53, and overexpressing MdWRKY53 enhanced AlCl3 tolerance in transgenic apple plants through the same mechanism as GR24. Subsequently, we identified MdPMEI45 (encoding pectin methylesterase inhibitor) and MdALS3 (encoding an Al transporter) as downstream target genes of MdWRKY53 using chromatin immunoprecipitation followed by sequencing (ChIP-seq). GR24 enhanced the interaction between MdWRKY53 and the transcription factor MdTCP15, further increasing the binding of MdWRKY53 to the MdPMEI45 promoter and inducing MdPMEI45 expression to prevent Al from crossing cell wall. MdWRKY53 also bound to the promoter of MdALS3 and enhanced its transcription to compartmentalize Al in vacuoles under AlCl3 stress. We therefore identified two modules involved in alleviating AlCl3 stress in woody plant apple: the SL-WRKY+TCP-PMEI module required for excluding external Al by blocking the entry of Al3+ into cells and the SL-WRKY-ALS module allowing internal detoxification of Al through vacuolar compartmentalization. These findings lay a foundation for the practical application of SLs in agriculture.

Supplemental Silicon and Boron Alleviates Aluminum-Induced Oxidative Damage in Soybean Roots

Aluminum (Al) toxicity in acidic soils is a major abiotic stress that negatively impacts plant growth and development. The toxic effects of Al manifest primarily in the root system, leading to inhibited root elongation and functionality, which impairs the above-ground organs of the plant. Recent research has greatly improved our understanding of the applications of small molecule compounds in alleviating Al toxicity. This study aimed to investigate the role of boron (B), silicon (Si), and their combination in alleviating Al toxicity in soybeans. The results revealed that the combined application significantly improved the biomass and length of soybean roots exposed to Al toxicity compared to B and Si treatments alone. Our results also indicated that Al toxicity causes programmed cell death (PCD) in soybean roots, while B, Si, and their combination all alleviated the PCD induced by Al toxicity. The oxidative damage induced by Al toxicity was noticeably alleviated, as evidenced by lower MAD and H2O2 accumulation in the soybean roots treated with the B and Si combination. Moreover, B, Si, and combined B and Si significantly enhanced plant antioxidant systems by up-regulating antioxidant enzymes including CAT, POD, APX, and SOD. Overall, supplementation with B, Si, and their combination was found to alleviate oxidative damage and reduce PCD caused by Al toxicity, which may be one of the mechanisms by which they alleviate root growth inhibition due to Al toxicity. Our results suggest that supplementation with B, Si, and their combination may be an effective strategy to improve soybean growth and productivity against Al toxicity.

Persulfidation maintains cytosolic G6PDs activity through changing tetrameric structure and competing cysteine sulfur oxidation under salt stress in Arabidopsis and tomato

Glucose-6-phosphate dehydrogenases (G6PDs) are essential regulators of cellular redox. Hydrogen sulfide (H2 S) is a small gasotransmitter that improves plant adaptation to stress; however, its role in regulating G6PD oligomerization to resist oxidative stress remains unknown in plants. Persulfidation of cytosolic G6PDs was analyzed by mass spectrometry (MS). The structural change model of AtG6PD6 homooligomer was built by chemical cross-linking coupled with mass spectrometry (CXMS). We isolated AtG6PD6C159A and SlG6PDCC155A transgenic lines to confirm the in vivo function of persulfidated sites with the g6pd5,6 background. Persulfidation occurs at Arabidopsis G6PD6 Cystine (Cys)159 and tomato G6PDC Cys155, leading to alterations of spatial distance between lysine (K)491-K475 from 42.0 Å to 10.3 Å within the G6PD tetramer. The structural alteration occurs in the structural NADP+ binding domain, which governs the stability of G6PD homooligomer. Persulfidation enhances G6PD oligomerization, thereby increasing substrate affinity. Under high salt stress, cytosolic G6PDs activity was inhibited due to oxidative modifications. Persulfidation protects these specific sites and prevents oxidative damage. In summary, H2 S-mediated persulfidation promotes cytosolic G6PD activity by altering homotetrameric structure. The cytosolic G6PD adaptive regulation with two kinds of protein modifications at the atomic and molecular levels is critical for the cellular stress response.

Potential xylose transporters regulated by CreA improved lipid yield and furfural tolerance in oleaginous yeast Saitozyma podzolica zwy-2-3

Lignocellulose's hydrolysate, a significant renewable source, contains xylose and furfural, making it challenging for industrial production of oleaginous yeast. On xylose fermentation with furfural treatment, OE::DN7263 and OE::DN7661 increased lipid yield and furfural tolerance versus WT, while, which of OE::CreA were decreased owing to CreA regulating DN7263 and DN7661 negatively. OE::CreA generated reactive oxygen species (ROS) causing oxidative damage. OE::DN7263, OE::DN7661, and ΔCreA reduced furfural via NADH; while ΔCreA produced less ROS and OE::DN7263, and OE::DN7661 scavenged ROS quickly, minimizing oxidative damage. Overall, CreA knockout increased DN7263 and DN7661 expression to facilitate xylose assimilation, enhancing NADH generation and ROS clearance. Finally, with mixed sugar fermentation, ΔCreA and OE::DN7263's biomass and lipid yield rose without furfural addition, while that of ΔCreA remained higher than WT after furfural treatment. These findings revealed how oleaginous yeast zwy-2-3 resisted furfural stress and indicated ΔCreA and OE::DN7263 might develop into robust industrial chassis strains.

In Silico RNAseq and Biochemical Analyses of Glucose-6-Phosphate Dehydrogenase (G6PDH) from Sweet Pepper Fruits: Involvement of Nitric Oxide (NO) in Ripening and Modulation

Pepper (Capsicum annuum L.) fruit is a horticultural product consumed worldwide which has great nutritional and economic relevance. Besides the phenotypical changes that pepper fruit undergo during ripening, there are many associated modifications at transcriptomic, proteomic, biochemical, and metabolic levels. Nitric oxide (NO) is a recognized signal molecule that can exert regulatory functions in diverse plant processes including fruit ripening, but the relevance of NADPH as a fingerprinting of the crop physiology including ripening has also been proposed. Glucose-6-phosphate dehydrogenase (G6PDH) is the first and rate-limiting enzyme of the oxidative phase of the pentose phosphate pathway (oxiPPP) with the capacity to generate NADPH. Thus far, the available information on G6PDH and other NADPH-generating enzymatic systems in pepper plants, and their expression during the ripening of sweet pepper fruit, is very scarce. Therefore, an analysis at the transcriptomic, molecular and functional levels of the G6PDH system has been accomplished in this work for the first time. Based on a data-mining approach to the pepper genome and fruit transcriptome (RNA-seq), four G6PDH genes were identified in pepper plants and designated CaG6PDH1 to CaG6PDH4, with all of them also being expressed in fruits. While CaG6PDH1 encodes a cytosolic isozyme, the other genes code for plastid isozymes. The time-course expression analysis of these CaG6PDH genes during different fruit ripening stages, including green immature (G), breaking point (BP), and red ripe (R), showed that they were differentially modulated. Thus, while CaG6PDH2 and CaG6PDH4 were upregulated at ripening, CaG6PDH1 was downregulated, and CaG6PDH3 was slightly affected. Exogenous treatment of fruits with NO gas triggered the downregulation of CaG6PDH2, whereas the other genes were positively regulated. In-gel analysis using non-denaturing PAGE of a 50-75% ammonium-sulfate-enriched protein fraction from pepper fruits allowed for identifying two isozymes designated CaG6PDH I and CaG6PDH II, according to their electrophoretic mobility. In order to test the potential modulation of such pepper G6PDH isozymes, in vitro analyses of green pepper fruit samples in the presence of different compounds including NO donors (S-nitrosoglutathione and nitrosocysteine), peroxynitrite (ONOO-), a hydrogen sulfide (H2S) donor (NaHS, sodium hydrosulfide), and reducing agents such as reduced glutathione (GSH) and L-cysteine (L-Cys) were assayed. While peroxynitrite and the reducing compounds provoked a partial inhibition of one or both isoenzymes, NaHS exerted 100% inhibition of the two CaG6PDHs. Taken together these data provide the first data on the modulation of CaG6PDHs at gene and activity levels which occur in pepper fruit during ripening and after NO post-harvest treatment. As a consequence, this phenomenon may influence the NADPH availability for the redox homeostasis of the fruit and balance its active nitro-oxidative metabolism throughout the ripening process.

Laser capture microdissection-based spatiotemporal transcriptomes uncover regulatory networks during seed abortion in seedless Ponkan (Citrus reticulata)

Seed abortion is an important process in the formation of seedless characteristics in citrus fruits. However, the molecular regulatory mechanism underlying citrus seed abortion is poorly understood. Laser capture microdissection-based RNA-seq combined with Pacbio-seq was used to profile seed development in the Ponkan cultivars 'Huagan No. 4' (seedless Ponkan) (Citrus reticulata) and 'E'gan No. 1' (seeded Ponkan) (C. reticulata) in two types of seed tissue across three developmental stages. Through comparative transcriptome and dynamic phytohormone analyses, plant hormone signal, cell division and nutrient metabolism-related processes were revealed to play critical roles in the seed abortion of 'Huagan No. 4'. Moreover, several genes may play indispensable roles in seed abortion of 'Huagan No. 4', such as CrWRKY74, CrWRKY48 and CrMYB3R4. Overexpression of CrWRKY74 in Arabidopsis resulted in severe seed abortion. By analyzing the downstream regulatory network, we further determined that CrWRKY74 participated in seed abortion regulation by inducing abnormal programmed cell death. Of particular importance is that a preliminary model was proposed to depict the regulatory networks underlying seed abortion in citrus. The results of this study provide novel insights into the molecular mechanism across citrus seed development, and reveal the master role of CrWRKY74 in seed abortion of 'Huagan No. 4'.

S-Nitrosoglutathione (GSNO)-Mediated Lead Detoxification in Soybean through the Regulation of ROS and Metal-Related Transcripts

Heavy metal toxicity, including lead (Pb) toxicity, is increasing in soils, and heavy metals are considered to be toxic in small amounts. Pb contamination is mainly caused by industrialization (e.g., smelting and mining), agricultural practices (e.g., sewage sludge and pests), and urban practices (e.g., lead paint). An excessive concentration of Pb can seriously damage and threaten crop growth. Furthermore, Pb adversely affects plant growth and development by affecting the photosystem, cell membrane integrity, and excessive production of reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) and superoxide (O₂^-). Nitric oxide (NO) is produced via enzymatic and non-enzymatic antioxidants to scavenge ROS and lipid peroxidation substrates to protect cells from oxidative damage. Thus, NO improves ion homeostasis and confers resistance to metal stress. In the present study, we investigated the effect of exogenously applied NO and S-nitrosoglutathione in soybean plants Our results demonstrated that exogenously applied NO aids in better growth under lead stress due to its ability in sensing, signaling, and stress tolerance in plants under heavy metal stress along with lead stress. In addition, our results showed that S-nitrosoglutathione (GSNO) has a positive effect on soybean seedling growth under lead-induced toxicity and that NO supplementation helps to reduce chlorophyll maturation and relative water content in leaves and roots following strong bursts under lead stress. GSNO supplementation (200 µM and 100 µM) reduced compaction and approximated the oxidative damage of MDA, proline, and H₂O₂. Moreover, under plant stress, GSNO application was found to relieve the oxidative damage by reactive oxygen species (ROS) scavenging. Additionally, modulation of NO and phytochelatins (PCS) after prolonged metal reversing GSNO application confirmed detoxification of ROS induced by the toxic metal lead in soybean. In summary, the detoxification of ROS caused by toxic metal concentrations in soybean is confirmed by using NO, PCS, and traditionally sustained concentrations of metal reversing GSNO application.

GmABR1 encoding an ERF transcription factor enhances the tolerance to aluminum stress in Arabidopsis thaliana

The ethylene response factor (ERF) transcription factors, which is one of the largest transcription factor families in plants, are involved in biological and abiotic stress response and play an important role in plant growth and development. In this study, the GmABR1 gene from the soybean inbred line Zhonghuang24 (ZH24)×Huaxia 3 (HX3) was investigated its aluminum (Al) tolerance. GmABR1 protein has a conserved domain AP2, which is located in the nucleus and has transcriptional activation ability. The results of real-time quantitative PCR (qRT-PCR) showed that the GmABR1 gene presented a constitutive expression pattern rich in the root tip, stem and leaf tissues of HX3. After Al stress, the GmABR1 transcript was significantly increased in the roots. The transcripts of GmABR1 in the roots of HX3 treated with 50 µM AlCl₃ was 51 times than that of the control. The GmABR1 was spatiotemporally specific with the highest expression levels when Al concentration was 50 µM, which was about 36 times than that of the control. The results of hematoxylin staining showed that the root tips of GmABR1-overexpression lines were stained the lightest, followed by the control, and the root tips of GmABR1 RNAi lines were stained the darkest. The concentrations of Al³⁺ in root tips were 207.40 µg/g, 147.74 µg/g and 330.65 µg/g in wild type (WT), overexpressed lines and RNAi lines, respectively. When AlCl₃ (pH4.5) concentration was 100 µM, all the roots of Arabidopsis were significantly inhibited. The taproot elongation of WT, GmABR1 transgenic lines was 69.6%, 85.6%, respectively. When treated with Al, the content of malondialdehyde (MDA) in leaves of WT increased to 3.03 µg/g, while that of transgenic Arabidopsis increased from 1.66-2.21 µg/g, which was lower than that of WT. Under the Al stress, the Al stress responsive genes such as AtALMT1 and AtMATE, and the genes related to ABA pathway such as AtABI1, AtRD22 and AtRD29A were up-regulated. The results indicated that GmABR1 may jointly regulate plant resistance to Al stress through genes related to Al stress response and ABA response pathways.

ZmG6PDH1 in glucose-6-phosphate dehydrogenase family enhances cold stress tolerance in maize

Glucose-6-phosphate dehydrogenase (G6PDH) is a key enzyme in the pentose phosphate pathway responsible for the generation of nicotinamide adenine dinucleotide phosphate (NADPH), thereby playing a central role in facilitating cellular responses to stress and maintaining redox homeostasis. This study aimed to characterize five G6PDH gene family members in maize. The classification of these ZmG6PDHs into plastidic and cytosolic isoforms was enabled by phylogenetic and transit peptide predictive analyses and confirmed by subcellular localization imaging analyses using maize mesophyll protoplasts. These ZmG6PDH genes exhibited distinctive expression patterns across tissues and developmental stages. Exposure to stressors, including cold, osmotic stress, salinity, and alkaline conditions, also significantly affected the expression and activity of the ZmG6PDHs, with particularly high expression of a cytosolic isoform (ZmG6PDH1) in response to cold stress and closely correlated with G6PDH enzymatic activity, suggesting that it may play a central role in shaping responses to cold conditions. CRISPR/Cas9-mediated knockout of ZmG6PDH1 on the B73 background led to enhanced cold stress sensitivity. Significant changes in the redox status of the NADPH, ascorbic acid (ASA), and glutathione (GSH) pools were observed after exposure of the zmg6pdh1 mutants to cold stress, with this disrupted redox balance contributing to increased production of reactive oxygen species and resultant cellular damage and death. Overall, these results highlight the importance of cytosolic ZmG6PDH1 in supporting maize resistance to cold stress, at least in part by producing NADPH that can be used by the ASA-GSH cycle to mitigate cold-induced oxidative damage.

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.

Aluminum stress signaling, response, and adaptive mechanisms in plants

Over 40% of arable land in the world is acidic. Al stress has become a global agricultural problem affecting plant growth and limiting crop production in acidic soils. Plants have evolved different regulatory mechanisms of adaptation to exogenous environmental challenges, such as Al stress, by altering their growth patterns. In the past decades, several key genes involved in plant response to Al stress and the mechanism of Al detoxification have been revealed. However, the signaling pathways of plant response to Al stress and the regulatory mechanism of plant Al tolerance remain poorly understood. In this review, we summarized the findings of recent studies on the plant Al tolerance mechanism and the molecular regulation mechanism of phytohormones in response to Al stress. This review improves our understanding of the regulatory mechanisms of plants in response to Al stress and provides a reference for the breeding of Al-tolerant crops.

A Chloroplast-Localized Glucose-6-Phosphate Dehydrogenase Positively Regulates Stripe Rust Resistance in Wheat

Glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme of the pentose phosphate pathway (PPP), plays a pivotal role in plant stress responses. However, the function and mechanism of G6PDHs in crop plants challenged by fungal pathogens remain poorly understood. In this study, a wheat G6DPH gene responding to infection by Puccinia striiformis f. sp. tritici (Pst), designated TaG6PDH2, was cloned and functionally identified. TaG6PDH2 expression was significantly upregulated in wheat leaves inoculated with Pst or treated with abiotic stress factors. Heterologous mutant complementation and enzymatic properties indicate that TaG6PDH2 encodes a G6PDH protein. The transient expression of TaG6PDH2 in Nicotiana benthamiana leaves and wheat protoplasts revealed that TaG6PDH2 is a chloroplast-targeting protein. Silencing TaG6PDH2 via the barley stripe mosaic virus (BSMV)-induced gene silencing (VIGS) system led to compromised wheat resistance to the Pst avirulent pathotype CYR23, which is implicated in weakened H2O2 accumulation and cell death. In addition, TaG6PDH2 was confirmed to interact with the wheat glutaredoxin TaGrxS4. These results demonstrate that TaG6PDH2 endows wheat with increased resistance to stripe rust by regulating reactive oxygen species (ROS) production.

Glucose-6-Phosphate Dehydrogenases: The Hidden Players of Plant Physiology

Glucose-6-phosphate dehydrogenase (G6PDH) catalyzes a metabolic hub between glycolysis and the pentose phosphate pathway (PPP), which is the oxidation of glucose-6-phosphate (G6P) to 6-phosphogluconolactone concomitantly with the production of nicotinamide adenine dinucleotide phosphate (NADPH), a reducing power. It is considered to be the rate-limiting step that governs carbon flow through the oxidative pentose phosphate pathway (OPPP). The OPPP is the main supplier of reductant (NADPH) for several "reducing" biosynthetic reactions. Although it is involved in multiple physiological processes, current knowledge on its exact role and regulation is still piecemeal. The present review provides a concise and comprehensive picture of the diversity of plant G6PDHs and their role in seed germination, nitrogen assimilation, plant branching, and plant response to abiotic stress. This work will help define future research directions to improve our knowledge of G6PDHs in plant physiology and to integrate this hidden player in plant performance.

Effects of Elevated Aluminum Concentration and Distribution on Root Damage, Cell Wall Polysaccharides, and Nutrient Uptake in Different Tolerant Eucalyptus Clones

Aluminized acidic soil can damage Eucalyptus roots and limit tree growth, hindering the productivity of Eucalyptus plantations. At present, the negative impacts of elevated aluminum (Al) on the cell morphology and cell wall properties of Eucalyptus root tip are still unclear. In order to investigate the responses of two different tolerant clones, Eucalyptus urophylla (G4) and Eucalyptus grandis × Eucalyptus urophylla (G9), to Al toxicity, seedling roots were treated hydroponically with an Al solution, and the polysaccharide content in the root tip cell wall and the characteristics of programmed cell death were studied. The results show that the distribution of Al was similar in both clones, although G9 was found to be more tolerant to Al toxicity than G4. The Al3+ uptake of pectin in root tip cell walls was significantly higher in G4 than in G9. The root tip in G4 was obviously damaged, enlarged, thickened, and shorter; the root crown cells were cracked and fluffy; and the cell elongation area was squeezed. The lower cell wall polysaccharide content and PME activity may result in fewer carboxylic groups in the root tip cell wall to serve as Al-binding sites, which may explain the stronger Al resistance of G9 than G4. The uptake of nitrogen and potassium in G4 was significantly reduced after aluminum application and was lower than in G9. Al-resistant Eucalyptus clones may have synergistic pleiotropic effects in resisting high aluminum-low phosphorus stress, and maintaining higher nitrogen and potassium levels in roots may be an important mechanism for effectively alleviating Al toxicity.

Glucose-6-phosphate dehydrogenase promotes the infection of Chilli veinal mottle virus through affecting ROS signaling in Nicotiana benthamiana

G6PDH negatively regulates viral accumulation in Nicotiana benthamiana through RBOHB-associated ROS signaling. Anti-oxidative metabolism and phytohormone-mediated immunity responses play important roles in virus infection. Glucose-6-phosphate dehydrogenase (G6PDH) is an enzyme in the pentose phosphate pathway, which plays an important role in maintaining intracellular redox homeostasis and has functions in plant growth, development and stress tolerance. However, the role of G6PDH in plants response to virus infection is poorly understood. In this study, NbG6PDH was found to be down-regulated after Chilli veinal mottle virus (ChiVMV-GFP) infection in Nicotiana benthamiana. Subcellular localization of NbG6PDH showed that it was punctate distributed in the protoplasm. Silencing of NbG6PDH reduced the sensitivity of N. benthamiana plants to ChiVMV-GFP. By contrast, transient overexpression of NbG6PDH promoted the accumulation of the virus. The results of physiological indexes showed that glutathione (GSH), catalase (CAT) and proline played an important role in maintaining plants physiological homeostasis. The results of gene expression detection showed that jasmonic acid/ethylene (JA/ET) signaling pathway was significantly correlated with the response of N. benthamiana to ChiVMV-GFP infection, and the changes of N. benthamiana respiratory burst oxidase homologues B (NbRBOHB) indicated that the NbG6PDH-dependent ROS may be regulated by NbRBOHB. Pretreatment of the inducer of reactive oxygen species (ROS) promoted virus infection, whereas inhibitor of ROS alleviated virus infection. Thus, our results indicate that the promoting effect of NbG6PDH on ChiVMV-GFP infection may be related to the NbRBOHB-regulated ROS production.

Autophagy alleviates indium-induced programmed cell death in wheat roots

Indium released in agroecosystems is becoming an emerging plant stressor, causing cellular damage and consequently crop yield losses. Previous studies have focused on indium-induced toxicity in plants, while plant adaptive responses to such emerging metal xenobiotics are poorly understood. Here, we explored the relationship of autophagy and programmed cell death (PCD) in wheat roots under indium stress. Indium treatment significantly decreased root activity and cell viability, and suppressed the length of root epidermal cells in the elongation zones. These symptoms may be associated with indium-induced PCD, as indium-stressed wheat roots displayed condensed and granular nuclei, increased number of TUNEL-positive nuclei, enhanced nuclear DNA fragmentation and caspase-3-like protease activity compared to untreated roots. Accordingly, indium enhanced the expression levels of TaMCA1 and TaMCA4, two major metacaspase genes mediated PCD in wheat plants. The enhanced expression of autophagy genes and formation of autophagosomes indicate that autophagy could regulate metabolic adaptation and repair stress-induced damage in wheat roots. Furthermore, reinforcing autophagy by activator rapamycin significantly decreased the number of TUNEL-positive nuclei and the activity of caspase-3-like protease, whereas inhibition of autophagy by 3-methyladenine aggravated diagnostic markers for PCD. These results together suggest that autophagy suppresses indium-induced PCD in wheat roots.