Glycolysis and de novo fatty acid synthesis cooperatively regulate pathological vascular smooth muscle cell phenotypic switching and neointimal hyperplasia.

Switching of vascular smooth muscle cells (VSMCs) from a contractile phenotype to a dedifferentiated (proliferative) phenotype contributes to neointima formation, which has been demonstrated to possess a tumor-like nature. Dysregulated glucose and lipid metabolism is recognized as a hallmark of tumors but has not thoroughly been elucidated in neointima formation. Here, we investigated the cooperative role of glycolysis and fatty acid synthesis in vascular injury-induced VSMC dedifferentiation and neointima formation. We found that the expression of hypoxia-inducible factor-1α (HIF-1α) and its target 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3), a critical glycolytic enzyme, were induced in the neointimal VSMCs of human stenotic carotid arteries and wire-injured mouse carotid arteries. HIF-1α overexpression led to elevated glycolysis and resulted in a decreased contractile phenotype while promoting VSMC proliferation and activation of the mechanistic target of rapamycin complex 1 (mTORC1). Conversely, silencing Pfkfb3 had the opposite effects. Mechanistic studies demonstrated that glycolysis generates acetyl coenzyme A to fuel de novo fatty acid synthesis and mTORC1 activation. Whole-transcriptome sequencing analysis confirmed the increased expression of PFKFB3 and fatty acid synthetase (FASN) in dedifferentiated VSMCs. More importantly, FASN upregulation was observed in neointimal VSMCs of human stenotic carotid arteries. Finally, interfering with PFKFB3 or FASN suppressed vascular injury-induced mTORC1 activation, VSMC dedifferentiation, and neointima formation. Together, this study demonstrated that PFKFB3-mediated glycolytic reprogramming and FASN-mediated lipid metabolic reprogramming are distinctive features of VSMC phenotypic switching and could be potential therapeutic targets for treating vascular diseases with neointima formation. © 2023 The Pathological Society of Great Britain and Ireland.

Integrated Metabolomics, Transcriptome and Functional Analysis Reveal Key Genes Are Involved in Tree Age-Induced Amino Acid Accumulation in Torreya grandis Nuts.

Torreya grandis is native Chinese tree species of economic significance, renowned for its long lifespan and the rich nutritional value of its nuts. In this study, we analyzed the morphological characteristics, metabolites, associated gene expressions, and regulatory mechanism in nuts from young (10 years old) and old (1000 years old) T. grandis trees. We observed that the length, width, and weight of nuts from older trees were considerably greater than those from younger trees. Metabolomic analysis revealed that the concentrations of 18 amino acids and derivatives (including histidine and serine) in nuts from older trees were markedly higher than those in nuts from younger trees. Transcriptome and metabolomic correlation analysis identified 16 genes, including TgPK (pyruvate kinase), TgGAPDH (glyceraldehyde 3-phosphate dehydrogenase), and others, which exhibit higher expression levels in older trees compared to younger trees, as confirmed by qRT-PCR. These genes are associated with the biosynthesis of histidine, glutamic acid, tryptophan, and serine. Transient expression of TgPK in tobacco led to increased pyruvate kinase activity and amino acid content (histidine, tryptophan, and serine). Additionally, dual-luciferase assays and yeast one-hybrid results demonstrated that TgWRKY21 positively regulates TgPK expression by directly binding to the TgPK promoter. These findings not only demonstrate the nutritional differences between nuts from young and old trees but also offer fresh insights into the development of nutritional sources and functional components based on nuts from old trees, enriching our understanding of the potential benefits of utilizing nuts from older trees.

Synthesis and Peroxide Activation Mechanism of Bimetallic MOF for Water Contaminant Degradation: A Review.

Metal-organic framework (MOF) materials possess a large specific surface area, high porosity, and atomically dispersed metal active sites, which confer excellent catalytic performance as peroxide (peroxodisulfate (PDS), peroxomonosulfate (PMS), and hydrogen peroxide (H2O2)) activation catalysts. However, the limited electron transfer characteristics and chemical stability of traditional monometallic MOFs restrict their catalytic performance and large-scale application in advanced oxidation reactions. Furthermore, the single-metal active site and uniform charge density distribution of monometallic MOFs result in a fixed activation reaction path of peroxide in the Fenton-like reaction process. To address these limitations, bimetallic MOFs have been developed to improve catalytic activity, stability, and reaction controllability in peroxide activation reactions. Compared with monometallic MOFs, bimetallic MOFs enhance the active site of the material, promote internal electron transfer, and even alter the activation path through the synergistic effect of bimetals. In this review, we systematically summarize the preparation methods of bimetallic MOFs and the mechanism of activating different peroxide systems. Moreover, we discuss the reaction factors that affect the process of peroxide activation. This report aims to expand the understanding of bimetallic MOF synthesis and their catalytic mechanisms in advanced oxidation processes.

The salt-activated CBF1/CBF2/CBF3-GALS1 module fine-tunes galactan-induced salt hypersensitivity in Arabidopsis.

Plant growth and development are significantly hampered in saline environments, limiting agricultural productivity. Thus, it is crucial to unravel the mechanism underlying plant responses to salt stress. ß-1,4-Galactan (galactan), which forms the side chains of pectic rhamnogalacturonan I, enhances plant sensitivity to high-salt stress. Galactan is synthesized by GALACTAN SYNTHASE1 (GALS1). We previously showed that NaCl relieves the direct suppression of GALS1 transcription by the transcription factors BPC1 and BPC2 to induce the excess accumulation of galactan in Arabidopsis (Arabidopsis thaliana). However, how plants adapt to this unfavorable environment remains unclear. Here, we determined that the transcription factors CBF1, CBF2, and CBF3 directly interact with the GALS1 promoter and repress its expression, leading to reduced galactan accumulation and enhanced salt tolerance. Salt stress enhances the binding of CBF1/CBF2/CBF3 to the GALS1 promoter by inducing CBF1/CBF2/CBF3 transcription and accumulation. Genetic analysis suggested that CBF1/CBF2/CBF3 function upstream of GALS1 to modulate salt-induced galactan biosynthesis and the salt response. CBF1/CBF2/CBF3 and BPC1/BPC2 function in parallel to regulate GALS1 expression, thereby modulating the salt response. Our results reveal a mechanism in which salt-activated CBF1/CBF2/CBF3 inhibit BPC1/BPC2-regulated GALS1 expression to alleviate galactan-induced salt hypersensitivity, providing an activation/deactivation fine-tune mechanism for dynamic regulation of GALS1 expression under salt stress in Arabidopsis.

Glycolysis inhibition ameliorates brain injury after ischemic stroke by promoting the function of myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells which are immunosuppressive and glycolytically inactive in inflammatory diseases. However, it is unknown whether MDSCs contribute to ischemic stroke and how glycolysis regulates MDSC function in such a context. Here, we showed that MDSCs arise in the blood of patients at early phase of stroke. Similar results were observed in temporary middle cerebral artery occlusion-induced cerebral ischemic mice. Pharmaceutical exhaustion of MDSCs aggravated, while adoptive transfer of MDSCs rescued the ischemic brain injury. However, the differentiation of MDSCs into immunopotent myeloid cells which coincides with increased glycolysis was observed in the context of ischemic stroke. Mechanistically, the glycolytic product lactate autonomously induces MDSC differentiation through activation of mTORC1, and paracrinely activates Th1 and Th17 cells. Moreover, gene knockout or inhibition of the glycolytic enzyme PFKFB3 increased endogenous MDSCs by blocking their differentiation, and improved ischemic brain injury. Collectively, these results revealed that glycolytic switch decreases the immunosuppressive and neuroprotective role of MDSCs in ischemic stroke and pharmacological targeting MDSCs via glycolysis inhibition constitutes a promising therapeutic strategy for ischemic stroke.

Synthesis of core-heteroshell structure for ZIF-67/VTM and its efficient activation of peroxymonosulfate in treatment of levofloxacin from an aqueous solution.

A core-heteroshell structural magnetic composite of ZIF-67/Vanadium-titanium magnetite (VTM) was successfully synthesized through a feasible solvothermal method and efficiently used in activation of peroxymonosulfate (PMS) for the treatment of levofloxacin (LVF) in an aqueous solution. The catalytic activity of the ZIF-67/VTM composite in LVF degradation was thoroughly evaluated, demonstrating the LVF removal rate could reach up to 93.3% within 60 min at ZIF-67/VTM composite dosage of 100 mg/L, PMS concertation of 75 mg/L, and the natural pH of 6.4. It is quite interesting that the carbon organic skeleton (in the ZIF-67 shell) have accelerated the internal electron transformation rate of the ZIF-67/VTM composite, thus efficiently promoting the O-O band (in PMS) breakage and the redox cycle of cobalt, further favoring the free radicals generation. The quenching experiments and EPR analysis results demonstrated that ·SO4- would play a crucial role in the LVF degradation process. Surprisingly, we have found that the introduction of Cl- (at some certain dosage) would not always decrease the LVF degradation ratio, for a new reactive oxygen species (singlet oxygen) was emerged in this system. What's more, the ZIF-67 (as the wrapping structure) could stabilize the VTM (the inner structure) in changing reaction conditions, prompting a good adaptability at a wider pH range (3-10) for inhibiting the leaching of various metal ions into the aqueous solution. This novel ZIF-67/VTM composite could provide new ideas and routes for the removal of emerging pollutants from an aqueous solution.

Phosphorylation of ZmNAC84 at Ser-113 enhances the drought tolerance by directly modulating ZmSOD2 expression in maize.

NAC (NAM, ATAF1/2, and CUC2) transcription factors play vital roles in response to multiple abiotic stresses. Our previous study has demonstrated that ZmNAC84, a maize NAC transcription factor, enhanced the drought tolerance by increasing abscisic acid (ABA)-induced antioxidant enzyme activities of APX and SOD, and Ser-113, a key phosphorylation site, of ZmNAC84 played an important role in this process. However, the target gene of ZmNAC84 in this process is still unknown. Here, we found that ZmNAC84 only regulated the luciferase activity driven by ZmSOD2 promoter in tobacco. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) assay showed that ZmNAC84 directly bound to the CACGTG motif of ZmSOD2 promoter. Furthermore, phosphorylation of ZmNAC84 at Ser-113 up-regulated the ZmSOD2 expression by enhancing the DNA binding ability of ZmNAC84 to ZmSOD2 promoter and improved the drought tolerance. Taken together, our results demonstrate that ZmNAC84 directly regulates ZmSOD2 expression to enhance drought tolerance and Ser-113 of ZmNAC84 is crucial in this process.

BRASSINOSTEROID-SIGNALING KINASE 1 phosphorylating CALCIUM/CALMODULIN-DEPENDENT PROTEIN KINASE functions in drought tolerance in maize.

Drought stress seriously limits crop productivity. Although studies have been carried out, it is still largely unknown how plants respond to drought stress. Here we find that drought treatment can enhance the phosphorylation activity of brassinosteroid-signaling kinase 1 (ZmBSK1) in maize (Zea mays). Our genetic studies reveal that ZmBSK1 positively affects drought tolerance in maize plants. ZmBSK1 localizes in plasma membrane, interacts with calcium/calmodulin (Ca2+ /CaM)-dependent protein kinase (ZmCCaMK), and phosphorylates ZmCCaMK. Ser-67 is a crucial phosphorylation site of ZmCCaMK by ZmBSK1. Drought stress enhances not only the interaction between ZmBSK1 and ZmCCaMK but also the phosphorylation of Ser-67 in ZmCCaMK by ZmBSK1. Furthermore, Ser-67 phosphorylation in ZmCCaMK regulates its Ca2+ /CaM binding, autophosphorylation and transphosphorylation activity, and positively affects its function in drought tolerance in maize. Our results reveal an important role for ZmBSK1 in drought tolerance and suggest a direct regulatory mode of ZmBSK1 phosphorylating ZmCCaMK.

ZmMPK5 phosphorylates ZmNAC49 to enhance oxidative stress tolerance in maize.

Mitogen-activated protein kinase (MPK) is a critical regulator of the antioxidant defence system in response to various stimuli. However, how MPK directly and exactly regulates antioxidant enzyme activities is still unclear. Here, we demonstrated that a NAC transcription factor ZmNAC49 mediated the regulation of antioxidant enzyme activities by ZmMPK5. ZmNAC49 expression is induced by oxidative stress. ZmNAC49 enhances oxidative stress tolerance in maize, and it also reduces superoxide anion generation and increases superoxide dismutase (SOD) activity. A detailed study showed that ZmMPK5 directly interacts with and phosphorylates ZmNAC49 in vitro and in vivo. ZmMPK5 directly phosphorylates Thr-26 in NAC subdomain A of ZmNAC49. Mutation at Thr-26 of ZmNAC49 does not affect the interaction with ZmMPK5 and its subcellular localisation. Further analysis found that ZmNAC49 activates the ZmSOD3 expression by directly binding to its promoter. ZmMPK5-mediated ZmNAC49 phosphorylation improves its ability to bind to the ZmSOD3 promoter. Thr-26 of ZmNAC49 is essential for its transcriptional activity. In addition, ZmSOD3 enhances oxidative stress tolerance in maize. Our results show that phosphorylation of Thr-26 in ZmNAC49 by ZmMPK5 increased its DNA-binding activity to the ZmSOD3 promoter, enhanced SOD activity and thereby improved oxidative stress tolerance in maize.

The transcription factor ZmNAC49 reduces stomatal density and improves drought tolerance in maize.

Drought stress severely limits the growth, development, and productivity of crops, and therefore understanding the mechanisms by which plants respond to drought is crucial. In this study, we cloned a maize NAC transcription factor, ZmNAC49, and identified its function in response to drought stress. We found that ZmNAC49 is localized in the nucleus and has transcriptional activation activity. ZmNAC49 expression is rapidly and strongly induced by drought stress, and overexpression enhances stress tolerance in maize. Overexpression also significant decreases the transpiration rate, stomatal conductance, and stomatal density in maize. Detailed study showed that ZmNAC49 overexpression affects the expression of genes related to stomatal development, namely ZmTMM, ZmSDD1, ZmMUTE, and ZmFAMA. In addition, we found that ZmNAC49 can directly bind to the promoter of ZmMUTE and suppress its expression. Taken together, our results show that the transcription factor ZmNAC49 represses ZmMUTE expression, reduces stomatal density, and thereby enhances drought tolerance in maize.

Caffeine promotes angiogenesis through modulating endothelial mitochondrial dynamics.

Caffeine induces multiple vascular effects. In this study we investigated the angiogenic effect of physiological concentrations of caffeine with focus on endothelial cell behaviors (migration and proliferation) during angiogenesis and its mitochondrial and bioenergetic mechanisms. We showed that caffeine (10-50 µM) significantly enhanced angiogenesis in vitro, evidenced by concentration-dependent increases in tube formation, and migration of human umbilical vein endothelial cells (HUVECs) without affecting cell proliferation. Caffeine (50 µM) enhanced endothelial migration via activation of cAMP/PKA/AMPK signaling pathway, which was mimicked by cAMP analog 8-Br-cAMP, and blocked by PKA inhibitor H89, adenylate cyclase inhibitor SQ22536 or AMPK inhibitor compound C. Furthermore, caffeine (50 µM) induced significant mitochondrial shortening through the increased phosphorylation of mitochondrial fission protein dynamin-related protein 1 (Drp1) in HUVECs, which increased its activity to regulate mitochondrial fission. Pharmacological blockade of Drp1 by Mdivi-1 (10 µM) or disturbance of mitochondrial fission by Drp1 silencing markedly suppressed caffeine-induced lamellipodia formation and endothelial cell migration. Moreover, we showed that caffeine-induced mitochondrial fission led to accumulation of more mitochondria in lamellipodia regions and augmentation of mitochondrial energetics, both of which were necessary for cell migration. In a mouse model of hindlimb ischemia, administration of caffeine (0.05% in 200 mL drinking water daily, for 14 days) significantly promoted angiogenesis and perfusion as well as activation of endothelial AMPK signaling in the ischemic hindlimb. Taken together, caffeine induces mitochondrial fission through cAMP/PKA/AMPK signaling pathway. Mitochondrial fission is an integral process in caffeine-induced endothelial cell migration by altering mitochondrial distribution and energetics.

Transcriptome analysis provides insights into the non-methylated lignin synthesis in Paphiopedilum armeniacum seed.

BACKGROUNDS: Paphiopedilum is an important genus of the orchid family Orchidaceae and has high horticultural value. The wild populations are under threat of extinction because of overcollection and habitat destruction. Mature seeds of most Paphiopedilum species are difficult to germinate, which severely restricts their germplasm conservation and commercial production. The factors inhibiting germination are largely unknown. RESULTS: In this study, large amounts of non-methylated lignin accumulated during seed maturation of Paphiopedilum armeniacum (P. armeniacum), which negatively correlates with the germination rate. The transcriptome profiles of P. armeniacum seed at different development stages were compared to explore the molecular clues for non-methylated lignin synthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that a large number of genes associated with phenylpropanoid biosynthesis and phenylalanine metabolism during seed maturation were differentially expressed. Several key genes in the lignin biosynthetic pathway displayed different expression patterns during the lignification process. PAL, 4CL, HCT, and CSE upregulation was associated with C and H lignin accumulation. The expression of CCoAOMT, F5H, and COMT were maintained at a low level or down-regulated to inhibit the conversion to the typical G and S lignin. Quantitative real-time RT-PCR analysis confirmed the altered expression levels of these genes in seeds and vegetative tissues. CONCLUSIONS: This work demonstrated the plasticity of natural lignin polymer assembly in seed and provided a better understanding of the molecular mechanism of seed-specific lignification process.

Thr420 and Ser454 of ZmCCaMK play a crucial role in brassinosteroid-induced antioxidant defense in maize.

Calcium/calmodulin-dependent protein kinase (CCaMK) has been shown to play important roles in brassinosteroid (BR)-induced antioxidant defense and enhancing the tolerance of plants to drought stress. The autophosphorylation of CCaMK is a key step for the activation of CCaMK, thus promoting substrate phosphorylation. However, how CCaMK autophosphorylation function in BR-induced antioxidant defense is not known yet. Here, seven potential autophosphorylation sites of ZmCCaMK were identified using mass spectroscopy (liquid chromatography-tandem mass spectrometry [LC-MS/MS]) analysis. The transient gene expression analysis in maize protoplasts showed that Thr420 and Ser454 of ZmCCaMK were important for BR-induced antioxidant defense. Furthermore, Thr420 and Ser454 of ZmCCaMK were crucial for improving drought tolerance and alleviating drought induced oxidative damage of plants via overexpressing various mutant versions of ZmCCaMK in tobacco (Nicotiana tabacum). Mutations of Thr420 and Ser454 in ZmCCaMK substantially blocked the autophosphorylation and substrate phosphorylation of ZmCCaMK in vitro. Taken together, our results demonstrate that Thr420 and Ser454 of ZmCCaMK are crucial for BR-induced antioxidant defense and drought tolerance through modulating the autophosphorylation and substrate phosphorylation activities of ZmCCaMK.

Abscisic acid positively regulates l-arabinose metabolism to inhibit seed germination through ABSCISIC ACID INSENSITIVE4-mediated transcriptional promotions of MUR4 in Arabidopsis thaliana.

l-Arabinose (l-Ara) is a major monosaccharide in plant polysaccharides and glycoproteins, and functions in plant growth and development. However, the potential role of l-Ara during abscisic acid (ABA)-mediated seed germination has been largely ignored. Here, our results showed a function of l-Ara during ABA-mediated seed germination. ABA slowed down the reduction of l-Ara in seed cell wall, and exogenous l-Ara aggravated the inhibition of ABA on germination. We further found that MUR4, encoding URIDINE 5'-DIPHOSPHATE-d-XYLOSE 4-EPIMERASE 1, played a vital role in ABA-mediated germination. MUR4 was highly expressed in embryo and induced by ABA in both seeds and seedlings. Overexpression of MUR4 conferred hypersensitive seed germination and early postgermination growth to ABA. Further analysis revealed that ABSCISIC ACID INSENSITIVE4 (ABI4) positively modulated the MUR4 expression by directly binding the Coupling Element1 motif of MUR4 promoter. Consistently, abi4-1 mutant had a lower l-Ara content in seed cell wall, while a higher l-Ara content in seed cell wall was observed in ABI4 overexpressors. Genetic analysis suggested that overexpression of MUR4 in abi4-1 partly restored the ABA sensitivity of abi4-1. We established the link between ABA and l-Ara during ABA-mediated seed germination and cotyledon greening in Arabidopsis and revealed the potential molecular mechanism.

TBL10 is required for O-acetylation of pectic rhamnogalacturonan-I in Arabidopsis thaliana.

O-Acetylated pectins are abundant in the primary cell wall of plants and growing evidence suggests they have important roles in plant cell growth and interaction with the environment. Despite their importance, genes required for O-acetylation of pectins are still largely unknown. In this study, we showed that TRICHOME BIREFRINGENCE LIKE 10 (AT3G06080) is involved in O-acetylation of pectins in Arabidopsis (Arabidopsis thaliana). The activity of the TBL10 promoter was strong in tissues where pectins are highly abundant (e.g. leaves). Two homozygous knock-out mutants of Arabidopsis, tbl10-1 and tbl10-2, were isolated and shown to exhibit reduced levels of wall-bound acetyl esters, equivalent of ~50% of the wild-type level in pectin-enriched fractions derived from leaves. Further fractionation revealed that the degree of acetylation of the pectin rhamnogalacturonan-I (RG-I) was reduced in the tbl10 mutant compared to the wild type, whereas the pectin homogalacturonan (HG) was unaffected. The degrees of acetylation in hemicelluloses (i.e. xyloglucan, xylan and mannan) were indistinguishable between the tbl10 mutants and the wild type. The mutant plants contained normal trichomes in leaves and exhibited a similar level of susceptibility to the phytopathogenic microorganisms Pseudomonas syringae pv. tomato DC3000 and Botrytis cinerea; while they displayed enhanced tolerance to drought. These results indicate that TBL10 is required for O-acetylation of RG-I, possibly as an acetyltransferase, and suggest that O-acetylated RG-I plays a role in abiotic stress responses in Arabidopsis.

GLUCOSAMINE INOSITOLPHOSPHORYLCERAMIDE TRANSFERASE1 (GINT1) Is a GlcNAc-Containing Glycosylinositol Phosphorylceramide Glycosyltransferase.

Glycosylinositol phosphorylceramides (GIPCs), which have a ceramide core linked to a glycan headgroup of varying structures, are the major sphingolipids in the plant plasma membrane. Recently, we identified the major biosynthetic genes for GIPC glycosylation in Arabidopsis (Arabidopsis thaliana) and demonstrated that the glycan headgroup is essential for plant viability. However, the function of GIPCs and the significance of their structural variation are poorly understood. Here, we characterized the Arabidopsis glycosyltransferase GLUCOSAMINE INOSITOLPHOSPHORYLCERAMIDE TRANSFERASE1 (GINT1) and showed that it is responsible for the glycosylation of a subgroup of GIPCs found in seeds and pollen that contain GlcNAc and GlcN [collectively GlcN(Ac)]. In Arabidopsis gint1 plants, loss of the GlcN(Ac) GIPCs did not affect vegetative growth, although seed germination was less sensitive to abiotic stress than in wild-type plants. However, in rice, where GlcN(Ac) containing GIPCs are the major GIPC subgroup in vegetative tissue, loss of GINT1 was seedling lethal. Furthermore, we could produce, de novo, "rice-like" GlcN(Ac) GIPCs in Arabidopsis leaves, which allowed us to test the function of different sugars in the GIPC headgroup. This study describes a monocot GIPC biosynthetic enzyme and shows that its Arabidopsis homolog has the same biochemical function. We also identify a possible role for GIPCs in maintaining cell-cell adhesion.

Xyloglucan endotransglucosylase-hydrolase30 negatively affects salt tolerance in Arabidopsis.

Plants have evolved various strategies to sense and respond to saline environments, which severely reduce plant growth and limit agricultural productivity. Alteration to the cell wall is one strategy that helps plants adapt to salt stress. However, the physiological mechanism of how the cell wall components respond to salt stress is not fully understood. Here, we show that expression of XTH30, encoding xyloglucan endotransglucosylase-hydrolase30, is strongly up-regulated in response to salt stress in Arabidopsis. Loss-of-function of XTH30 leads to increased salt tolerance and overexpression of XTH30 results in salt hypersensitivity. XTH30 is located in the plasma membrane and is highly expressed in the root, flower, stem, and etiolated hypocotyl. The NaCl-induced increase in xyloglucan (XyG)-derived oligosaccharide (XLFG) of the wild type is partly blocked in xth30 mutants. Loss-of-function of XTH30 slows down the decrease of crystalline cellulose content and the depolymerization of microtubules caused by salt stress. Moreover, lower Na+ accumulation in shoot and lower H2O2 content are found in xth30 mutants in response to salt stress. Taken together, these results indicate that XTH30 modulates XyG side chains, altered abundance of XLFG, cellulose synthesis, and cortical microtubule stability, and negatively affecting salt tolerance.

Loss of Inositol Phosphorylceramide Sphingolipid Mannosylation Induces Plant Immune Responses and Reduces Cellulose Content in Arabidopsis.

Glycosylinositol phosphorylceramides (GIPCs) are a class of glycosylated sphingolipids found in plants, fungi, and protozoa. These lipids are abundant in the plant plasma membrane, forming ∼25% of total plasma membrane lipids. Little is known about the function of the glycosylated headgroup, but two recent studies have indicated that they play a key role in plant signaling and defense. Here, we show that a member of glycosyltransferase family 64, previously named ECTOPICALLY PARTING CELLS1, is likely a Golgi-localized GIPC-specific mannosyl-transferase, which we renamed GIPC MANNOSYL-TRANSFERASE1 (GMT1). Sphingolipid analysis revealed that the Arabidopsis thaliana gmt1 mutant almost completely lacks mannose-carrying GIPCs. Heterologous expression of GMT1 in Saccharomyces cerevisiae and tobacco (Nicotiana tabacum) cv Bright Yellow 2 resulted in the production of non-native mannosylated GIPCs. gmt1 displays a severe dwarfed phenotype and a constitutive hypersensitive response characterized by elevated salicylic acid and hydrogen peroxide levels, similar to that we previously reported for the Golgi-localized, GIPC-specific, GDP-Man transporter GONST1 (Mortimer et al., 2013). Unexpectedly, we show that gmt1 cell walls have a reduction in cellulose content, although other matrix polysaccharides are unchanged.

Pectin methylesterase31 positively regulates salt stress tolerance in Arabidopsis.

The alteration of cell wall component and structure is an important adaption to saline environment. Pectins, a major cell wall component, are often present in a highly methylesterified form. The level of methyl esterification determined by pectin methylesterases (PMEs) influences many important wall properties that are believed to relate to the adaption to saline stress. However, little is known about the function of PMEs in response to salt stress. Here, we established a link between pectin methylesterase31 (PME31) and salt stress tolerance. Salt stress significantly increases PME31 expression. PME31 is located in the plasma membrane and the expression level of PME31 was high in dry seeds. Knock-down mutants in PME31 conferred hypersensitive phenotypes to salt stress in seed germination and post-germination growth. Real-time PCR analysis revealed that the transcript levels of several stress genes (DREB2A, RD29A and RD29B) are lower in pme31-2 mutant than that in the wild type in response to salt stress. These results suggested that PME31 could positively modulate salt stress tolerance.

The NADPH-oxidase AtRbohI plays a positive role in drought-stress response in Arabidopsis thaliana.

As the major resource of reactive oxygen species (ROS), the NADPH oxidases (Rbohs) have been shown to play important roles in plant cells under normal growth and stress conditions. Although many family members of Rbohs were studied, little is known about the function of RbohI in Arabidopsis thaliana. Here, we report that exogenous ABA application decreases RbohI expression and mannitol significantly increases RbohI expression at transcript level. The RbohI transcripts were strongly detected in dry seeds and roots. The loss-of-function mutant rbohI exhibited sensitivity to ABA and mannitol stress during germination. Furthermore, the lateral root growth of rbohI was severely inhibited after treatment with mannitol stress. Overexpression of RbohI in Arabidopsis significantly improves the drought tolerance. Moreover, more H2O2 accumulated in RbohI overexpressors than in wild type plants in response to mannitol stress. Our conclusion is that AtRbohI functions in drought-stress response in Arabidopsis thaliana.