Winter wheat cells subjected to freezing temperature undergo death process with features of programmed cell death

Programmed cell death is a process defined as genetically regulated self-destruction or cell suicide. It can be activated by different internal and external factors, but few studies have investigated whether this process occurs under cold and freezing temperatures. In this study, a freezing treatment (-8 °C for 6 h) induced cell death with features of programmed cell death in suspension cultures of winter wheat (Triticum aestivum L.). This process occurred for 10 days after cold exposure. The death of cells in culture was slow and prolonged, and was accompanied by protoplast shrinkage, DNA fragmentation, and an increase in the level of reactive oxygen species. Other changes observed after the freezing treatment included an increase in the respiration rate, changes in mitochondrial transmembrane potential (∆Ψ m ), and the release of cytochrome c from mitochondria into the cytosol. These findings indicated that mitochondria are involved in the cell death process that occurs after a freezing treatment in cells of winter wheat.

TaADF7, an actin-depolymerizing factor, contributes to wheat resistance against Puccinia striiformis f. sp. tritici

The actin cytoskeleton is involved in plant defense responses; however, the role of the actin-depolymerizing factor (ADF) family, which regulates actin cytoskeletal dynamics, in plant disease resistance, is largely unknown. Here, we characterized a wheat (Triticum aestivum) ADF gene, TaADF7, with three copies located on chromosomes 1A, 1B, and 1D, respectively. All three copies encoded the same protein, although there were variations in 19 nucleotide positions in the open reading frame. Transcriptional expression of the three TaADF7 copies were all sharply elevated in response to avirulent Puccinia striiformis f. sp. tritici (Pst) infection, with similar expression patterns. TaADF7 regulated the actin cytoskeletal dynamics by targeting the actin cytoskeleton to execute actin binding/severing activities. When the TaADF7 copies were all silenced by virus-induced gene silencing, the growth of Pst hypha increased and sporadic urediniospores were observed, as compared with control plants, upon inoculation with avirulent Pst. In addition, the accumulation of reactive oxygen species (ROS) and the hypersensitive response (HR) were greatly weakened, whereas cytochalasin B partially rescued the HR in TaADF7 knock-down plants. Together, these findings suggest that TaADF7 is likely to contribute to wheat resistance against Pst infection by modulating the actin cytoskeletal dynamics to influence ROS accumulation and the HR.

Effects of nitrogen nutrition on the synthesis and deposition of the ω-gliadins of wheat

BACKGROUND AND AIMS

The ω-gliadin storage proteins of wheat are of interest in relation to their impact on grain processing properties and their role in food allergy, particularly the ω-5 sub-group and wheat-dependent exercise-induced anaphylaxis. The ω-gliadins are also known to be responsive to nitrogen application. This study therefore compares the effects of cultivar and nitrogen availability on the synthesis and deposition of ω-gliadins in wheat grown under field conditions in the UK, including temporal and spatial analyses at the protein and transcript levels.

METHODS

SDS-PAGE, western blotting and N-terminal amino acid sequencing were used to compare the patterns of ω-gliadin components in mature grain of six British wheat (Triticum aestivum) cultivars and their accumulation during the development of grain grown in field plots with varying nitrogen supply. Changes in gene expression during development were determined using real-time reverse transcription-PCR (RT-PCR). Spatial patterns of gene expression and protein accumulation were determined by in situ hybridization and immunofluorescence microscopy, respectively.

KEY RESULTS

Two patterns of ω-gliadins were identified in the six cultivars, including both monomeric 'gliadin' proteins and subunits present in polymeric 'glutenin' fractions. Increasing the level of nitrogen fertilizer in field plots resulted in increased expression of ω-gliadin transcripts and increased proportions of ω-5 gliadins. Nitrogen supply also affected the spatial patterns of ω-gliadin synthesis and deposition, which were differentially increased in the outer layers of the starchy endosperm with high levels of nitrogen.

CONCLUSIONS

Wheat ω-gliadins vary in amount and composition between cultivars, and in their response to nitrogen supply. Their spatial distribution is also affected by nitrogen supply, being most highly concentrated in the sub-aleurone cells of the starchy endosperm under higher nitrogen availability.

A genotypic difference in primary root length is associated with the inhibitory role of transforming growth factor-beta receptor-interacting protein-1 on root meristem size in wheat

Previously we identified a major quantitative trait locus (QTL) qTaLRO-B1 for primary root length (PRL) in wheat. Here we compare proteomics in the roots of the qTaLRO-B1 QTL isolines 178A, with short PRL and small meristem size, and 178B, with long PRL and large meristem size. A total of 16 differentially expressed proteins were identified: one, transforming growth factor (TGF)-beta receptor-interacting protein-1 (TaTRIP1), was enriched in 178A, while various peroxidases (PODs) were more abundantly expressed in 178B. The 178A roots showed higher TaTRIP1 expression and lower levels of the unphosphorylated form of the brassinosteroid (BR) signaling component BZR1, lower expression of POD genes and reduced POD activity and accumulation of the superoxide anion O2(-) in the root elongation zone compared with the 178B roots. Low levels of 24-epibrassinolide increased POD gene expression and root meristem size, and rescued the short PRL phenotype of 178A. TaTRIP1 directly interacted with the BR receptor TaBRI1 of wheat. Moreover, overexpressing TaTRIP1 in Arabidopsis reduced the abundance of unphosphorylated BZR1 protein, altered the expression of BR-responsive genes, inhibited POD activity and accumulation of the O2(-) in the root tip and inhibited root meristem size. Our data suggested that TaTRIP1 is involved in BR signaling and inhibited root meristem size, possibly by reducing POD activity and accumulation of O2(-) in the root tip. We further demonstrated a negative correlation between the level of TaTRIP1 mRNA and PRL of landraces and modern wheat varieties, providing a valuable insight for better understanding of the molecular mechanism underlying the genotypic differences in root morphology of wheat in the future.

Analysis of plant ribosomes with asymmetric flow field-flow fractionation

Ribosome profiling is a technique used to separate ribosomal subunits, 80S ribosomes (monosomes), and polyribosomes (polysomes) from other RNA-protein complexes. It is traditionally performed in sucrose gradients. In this study, we used asymmetric flow field-flow fractionation (AsFlFFF) to characterize ribosome profiles of Nicotiana benthamiana plants. With the optimized running conditions, we were able to separate free molecules from ribosomal subunits and intact ribosomes. We used various chemical and enzymatic treatments to validate the positions of subunits, monosomes, and polysomes in the AsFlFFF fractograms. We also characterized the protein and RNA content of AsFlFFF fractions by gel electrophoresis and western blotting. The reverse transcription polymerase chain reaction (RT-PCR) analysis showed that ribosomes remained bound to messenger RNAs (mRNAs) during the analysis. Therefore, we conclude that AsFlFFF can be used for ribosome profiling to study the mRNAs that are being translated. It can also be used to study the protein composition of ribosomes that are active in translation at that particular moment.

Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression

Hydrogen sulfide (H2S) is considered as a cellular signaling intermediate in higher plants, but corresponding molecular mechanisms and signal transduction pathways in plant biology are still limited. In the present study, a combination of pharmacological and biochemical approaches was used to study the effect of H2S on the alleviation of GA-induced programmed cell death (PCD) in wheat aleurone cells. The results showed that in contrast with the responses of ABA, GA brought about a gradual decrease of l-cysteine desulfhydrase (LCD) activity and H2S production, and thereafter PCD occurred. Exogenous H2S donor sodium hydrosulfide (NaHS) not only effectively blocked the decrease of endogenous H2S release, but also alleviated GA-triggered PCD in wheat aleurone cells. These responses were sensitive to hypotaurine (HT), a H2S scavenger, suggesting that this effect of NaHS was in an H2S-dependent fashion. Further experiment confirmed that H2S, rather than other sodium- or sulphur-containing compounds derived from the decomposing of NaHS, was attributed to the rescuing response. Importantly, the reversing effect was associated with glutathione (GSH) because the NaHS triggered increases of endogenous GSH content and the ratio of GSH/oxidized GSH (GSSG) in GA-treated layers, and the NaHS-mediated alleviation of PCD was markedly eliminated by l-buthionine-sulfoximine (BSO, a selective inhibitor of GSH biosynthesis). The inducible effect of NaHS was also ascribed to the modulation of heme oxygenase-1 (HO-1), because the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPP) significantly suppressed the NaHS-related responses. By contrast, the above inhibitory effects were reversed partially when carbon monoxide (CO) aqueous solution or bilirubin (BR), two of the by-products of HO-1, was added, respectively. NaHS-triggered HO-1 gene expression in GA-treated layers was also confirmed. Together, the above results clearly suggested that the H2S-delayed PCD in GA-treated wheat aleurone cells was associated with the modulation of GSH homeostasis and HO-1 gene expression.

The control of recombination in wheat by Ph1 and its use in breeding

Two meiotic processes have a major influence on the plant breeding, namely, the independent assortment of chromosomes, and recombination. The major chromosome pairing locus in hexaploid and tetraploid wheat, Ph1, has a significant effect on both these processes. This chapter reviews our current understanding of this locus and how mutants of it can be exploited for breeding purposes.

Ethylene and reactive oxygen species are involved in root aerenchyma formation and adaptation of wheat seedlings to oxygen-deficient conditions

Exposing plants to hypoxic conditions greatly improves their anoxic stress tolerance by enhancing the activities of glycolysis and fermentation in roots. Ethylene may also be involved in these adaptive responses because its synthesis is increased in roots under hypoxic conditions. Here it is reported that pre-treatment of wheat seedlings with an ethylene precursor, 1-aminocyclopropanecarboxylic acid (ACC), enhanced accumulation of ethylene in the roots of wheat seedlings, and enhanced their tolerance of oxygen-deficient conditions through increasing the expression of genes encoding ethanol fermentation enzymes, alcohol dehydrogenase and pyruvate decarboxylase, in the roots. Lysigenous aerenchyma formation in root was induced by ACC pre-treatment and was further induced by growth under oxygen-deficient conditions. ACC pre-treatment increased the expression of three genes encoding respiratory burst oxidase homologue (a plant homologue of gp91(phox) in NADPH oxidase), which has a role in the generation of reactive oxygen species (ROS), in roots of seedlings. Co-treatment with ACC and an NADPH oxidase inhibitor, diphenyleneiodonium, partly suppressed the ACC-induced responses. These results suggest that ethylene and ROS are involved in adaptation of wheat seedlings to oxygen-deficient conditions through controlling lysigenous aerenchyma formation and the expression of genes encoding ethanol fermentation enzymes.

Vernalization treatment induces site-specific DNA hypermethylation at the VERNALIZATION-A1 (VRN-A1) locus in hexaploid winter wheat

BACKGROUND

Certain temperate species require prolonged exposure to low temperature to initiate transition from vegetative growth to flowering, a process known as vernalization. In wheat, winter cultivars require vernalization to initiate flowering, making vernalization requirement a trait of key importance in wheat agronomy. The genetic bases of vernalization response have been largely studied in wheat, leading to the characterization of a regulation pathway that involves the key gene VERNALIZATION1 (VRN1). While previous studies in wheat and barley have revealed the functional role of histone modification in setting VRN1 expression, other mechanisms might also be involved. Here, we were interested in determining whether the cold-induced expression of the wheat VRN-A1 gene is associated with a change in DNA methylation.

RESULTS

We provide the first DNA methylation analysis of the VRN-A1 gene, and describe the existence of methylation at CG but also at non CG sites. While CG sites show a bell-shape profile typical of gene-body methylation, non CG methylation is restricted to the large (8.5 kb) intron 1, in a region harboring fragments of transposable elements (TEs). Interestingly, cold induces a site-specific hypermethylation at these non CG sites. This increase in DNA methylation is transmitted through mitosis, and is reset to its original level after sexual reproduction.

CONCLUSIONS

These results demonstrate that VRN-A1 has a particular DNA methylation pattern, exhibiting rapid shift within the life cycle of a winter wheat plant following exposure to particular environmental conditions. The finding that this shift occurs at non CG sites in a TE-rich region opens interesting questions onto the possible consequences of this type of methylation in gene expression.

Process of aerenchyma formation and reactive oxygen species induced by waterlogging in wheat seminal roots

The development and regulation of aerenchyma in waterlogged conditions were studied in the seminal roots of wheat. Evans blue staining and the first cell death position indicated that the cortical cell death began at the root mid-cortex cells in flooding conditions. Continuous waterlogging treatment caused the spread of cell death from the mid-cortex to the neighboring cells and well-developed aerenchyma was formed after 72 h. Meanwhile, the formation of radial oxygen loss barrier was observed in the exodermis owing to the induction of Casparian bands and lignin deposition. Analysis of aerenchyma along the wheat root revealed that aerenchyma formed at 10 mm from the root tip, significantly increased toward the center of the roots, and decreased toward the basal region of the root. In situ detection of radial oxygen species (ROS) showed that ROS accumulation started in the mid-cortex cells, where cell death began indicating that cell death was probably accompanied by ROS production. Further waterlogging treatments resulted in the accumulation of ROS in the cortical cells, which were the zone for aerenchyma development. Accumulation and distribution of H₂O₂ at the subcellular level were revealed by ultracytochemical localization, which further verified the involvement of ROS in the cortical cell death process (i.e., aerenchyma formation). Furthermore, gene expression analysis indicated that ROS production might be the result of up-regulation of genes encoding for ROS-producing enzymes and the down-regulation of genes encoding for ROS-detoxifying enzymes. These results suggest that aerenchyma development in wheat roots starts in the mid-cortex cells and its formation is regulated by ROS.

Effects of waterlogging on amyloplasts and programmed cell death in endosperm cells of Triticum aestivum L

The effects of waterlogging on amyloplasts and programmed cell death (PCD) in endosperm cells in Chinese wheat (Triticum aestivum L.; cv: Hua mai 8) are here discussed. Four water treatments were established from anthesis to maturity: they were 3 days of waterlogging treatment (DWT), 7 DWT, 12 DWT, and moderate water supply (the control). Lugol staining and scanning electron microscopy showed decreases in the number of amyloplasts and partially filled circular cavities under the waterlogging treatments. These resulted in serious deformities in the endosperm cells. Evans blue staining analysis and terminal deoxynucleotidyl transferase-mediated fluorescein deoxyuridine triphosphate nick-end labeling assays indicated that the PCD progression of endosperm cells occurred earlier under waterlogging treatments than in the control, so did the internucleosomal DNA fragmentation, which accompanies PCD in endosperm cells. Electron transmission microscopy analysis showed similar results. Under waterlogging treatments, the following PCD characteristics appeared earlier and were more pronounced than in normal endosperm cells: chromatin condensation, degradation of the nuclear envelope, swelling, and degradation of the mitochondrial cristae. Our study concluded that under waterlogging conditions, the number of amyloplasts tended to decrease and PCD was likely to appear ahead of time.

Visualization and characterization of prolamellar bodies with atomic force microscopy

Prolamellar bodies (PLBs) isolated from etiolated wheat seedlings were studied with the use of atomic force microscopy (AFM), transmission electron microscopy (TEM) and fluorescence spectroscopy. With AFM, PLBs were seen as spherical structures about 1-2μm in diameter, more elastic than mica and poly-l-lysine substrate. TEM analyses confirmed that PLBs of wheat leaf etioplasts also had an average diameter of appr. 1μm. Illumination induced the photoreduction of photoactive protochlorophyllide (Pchlide), i.e. Pchlide bound to protochlorophyllide oxidoreductase, which was shown in fluorescence spectra. The photoreduction was followed by the disruption of PLB structures, which started with the enlargement of PLB spheres and then their fragmentation into small balls as seen with AFM. Light-induced vesicle formation and the outgrowth of lamellar (pro)thylakoid membranes on the PLB surface were also confirmed by TEM analyses, and resulted in the apparent enlargement of the PLB diameter. The blue-shift of the fluorescence emission maximum of chlorophyllide observed for PLBs at room temperature after Pchlide photoreduction was completed within 25min. However, structural changes in PLBs were still observed after the completion of the blue-shift. The incubation of PLBs in darkness with HgCl2 also resulted in PLB enlargement and a loosening of their structure. AFM provides a unique opportunity to observe PLBs at a physiological temperature without the necessity of fixation.

Microdissection and chromosome painting of the alien chromosome in an addition line of wheat--Thinopyrum intermedium

In this study, chromosome painting was developed and used to identify alien chromosomes in TAi-27, a wheat - Thinopyrumintermedium addition line, and the chromosomes of the three different genomes of Th. Intermedium. The smallest alien chromosome of TAi-27 was microdissected and its DNA amplified by DOP-PCR was used as a probe to hybridize with metaphase chromosomes of TAi-27 and Th. intermedium. Results showed that hybridization signals were observed in all regions of a pair of the smallest alien chromosomes and the pericentromeric area of another pair of alien chromosomes in TAi-27, indicating that the probe from microdissected chromosome is species specific. In Th. intermedium, 14 chromosomes had wide and strong hybridization signals distributed mainly on the pericentromere area and 9 chromosomes with narrow and weak signals on the pericentromere area. The remaining chromosomes displayed a very weak or no signal. Sequential FISH/GISH on Th. intermedium chromosomes using the DNAs of microdissected chromosome, Pseudoroegneriaspicata (St genome) and pDbH12 (a J^s genome specific probe) as the probes indicated that the microdissected chromosome belonged to the St genome, three genomes (J^s, J and St) in Th. intermedium could be distinguished, in which there is no hybridization signal on J genome that is similar to the genome of Th. bessarabicum. Our results showed that the smallest alien chromosomes may represent a truncated chromosome and the repetitive sequence distribution might be similar in different chromosomes within the St genome. However, the repetitive sequence distributions are different within the J^s genome, within a single chromosome, and among different genomes in Th. intermedium. Our results suggested that chromosome painting could be feasible in some plants and useful in detecting chromosome variation and repetitive sequence distribution in different genomes of polyploidy plants, which is helpful for understanding the evolution of different genomes in polyploid plants.

Structural and physiological characterization during wheat pericarp development

The cytological and physiological features of developing wheat pericarp were clearly characterized in this report. Our results may be helpful to articulate the functions of pericarp during the seed development. Although wheat pericarp has been well studied, knowledge of the sequence of events in the process of pericarp development is incomplete. In the present study, the structural development process of wheat (Triticum aestivum L.) pericarp was investigated in detail using resin microtomy and microscopy. Chlorophyll contents, and photosynthetic and respiratory rates, in pericarp were determined using spectrophotometer and an oxygen electrode, respectively. Mineral nutrient contents were also determined using scanning electron microscopy. The main results are as follows: (1) based on the structures and physiological characteristics observed, the developmental process of pericarp was divided into four stages, growth, formation, extinction and maturation stages, pericarp exhibited specific features at each stage. (2) Pericarp development differed in different parts, or varieties, of wheat. The dorsal pericarp had fewer starch grains and slower rates of apoptosis than the abdominal mesocarp. The cross cells in dorsal pericarp had an irregular outline. When compared with soft wheat cv. Yangmai 11, mesocarp cells in hard wheat cv. Xumai 30 had more starch grains, larger cell size and longer development duration. (3) The chlorophyll content, photosynthesis rate and respiratory rate in pericarp increased gradually, reaching a maximum about 16 days after anthesis, and later decreased continually. The photosynthetic rate in pericarp was lower than the respiration rate. (4) The contents of mineral elements in pericarp, such as calcium, zinc, iron and potassium were higher than those in the inner endosperm. The data indicate that wheat pericarp has many functions, e.g. protection, photosynthesis, mineral accumulation, synthesis and degradation of starch.

Is floret primordia death triggered by floret development in durum wheat?

Survival of floret primordia initiated seems critical for the determination of grain number and yield in wheat, and understanding what determines floret mortality would help in the development of more robust physiological models of yield determination. The growth of the juvenile spikes has been frequently considered the determinant of grain number, implying that floret development would depend on resource availability and that the onset of floret death would be related to spike growth. However, this model has been recently challenged from a study concluding that floret death started when the most advanced floret primordia reached a particular developmental stage. As the few previous studies on this relationship involved photoperiod treatments which affect both floret development and the onset of spike growth, conclusions cannot be considered mechanistic. This comprehensive study analysed in detail floret development in wheat as affected by resource availability (mainly soil nitrogen levels) and found that the onset of floret death may occur when development of the most advanced florets ranged from stages 5 to 9 and that the average and standard deviation of floret developmental stage coinciding with the onset of floret death was not related to the level of availability of resources. These results provide further support to the model relating the onset of floret death with the initiation of active growth of the juvenile spike in which florets are developing.

Mechanisms regulating grain contamination with trichothecenes translocated from the stem base of wheat (Triticum aestivum) infected with Fusarium culmorum

Factors limiting trichothecene contamination of mature wheat grains after Fusarium infection are of major interest in crop production. In addition to ear infection, systemic translocation of deoxynivalenol (DON) may contribute to mycotoxin levels in grains after stem base infection with toxigenic Fusarium spp. However, the exact and potential mechanisms regulating DON translocation into wheat grains from the plant base are still unknown. We analyzed two wheat cultivars differing in susceptibility to Fusarium head blight (FHB), which were infected at the stem base with Fusarium culmorum in climate chamber experiments. Fungal DNA was found only in the infected stem base tissue, whereas DON and its derivative, DON-3-glucoside (D3G), were detected in upper plant parts. Although infected stem bases contained more than 10,000 μg kg⁻¹ dry weight (DW) of DON and mean levels of DON after translocation in the ear and husks reached 1,900 μg kg⁻¹ DW, no DON or D3G was detectable in mature grains. D3G quantification revealed that DON detoxification took mainly place in the stem basis, where ≤ 50% of DON was metabolized into D3G. Enhanced expression of a gene putatively encoding a uridine diphosphate-glycosyltransferase (GenBank accession number FG985273) was observed in the stem base after infection with F. culmorum. Resistance to F. culmorum stem base infection, DON glycosylation in the stem base, and mycotoxin translocation were unrelated to cultivar resistance to FHB. Histological studies demonstrated that the vascular transport of DON labeled with fluorescein as a tracer from the peduncle to the grain was interrupted by a barrier zone at the interface between grain and rachilla, formerly described as "xylem discontinuity". This is the first study to demonstrate the effective control of influx of systemically translocated fungal mycotoxins into grains at the rachilla-seed interface by the xylem discontinuity tissue in wheat ears.

Functions of the lethal leaf-spot 1 gene in wheat cell death and disease tolerance to Puccinia striiformis

Pheophorbide a oxygenase (PaO) is a key enzyme in chlorophyll catabolism that is known to suppress cell death in maize and Arabidopsis. The catalytic activity of PaO in chlorophyll degradation has been clearly demonstrated, but the function of PaO in the regulation of cell death and plant-microbe interactions is largely unknown. In this study, we characterized a PaO homologue in wheat of the lethal leaf-spot 1 gene, TaLls1, that was induced in leaves infected by Puccinia striiformis f.sp. tritici (Pst) and wounding treatment. The TaLls1 protein contains a conserved Rieske [2Fe-2S] motif and a mononuclear iron-binding site typical of PaOs. Silencing of TaLls1 by virus-induced gene silencing in wheat led to leaf cell death without pathogen attacks, possibly due to the accumulation of pheophorbide a (upstream substrate of PaO), indicating a suppressor role of TaLls1, while overexpression of TaLls1 also triggered cell death in both tobacco and wheat leaves, probably owing to the accumulation of the red chlorophyll catabolite (downstream product of PaO). Further deletion mutant analysis showed that the conserved Rieske domain, but not the iron-binding site, was essential for cell death induction. These results thus suggest a threshold for TaLls1 in maintaining cell homeostasis to adapt in various stresses, and shed new light on the role of TaLls1 in cell death regulation. Furthermore, silencing of TaLls1 in wheat did not change the disease symptoms but enhanced tolerance to Pst via an significant increase in H2O2 generation, elevated cell death occurrence, and upregulation of pathogenesis-related genes.

Mobilization of lipids and fortification of cell wall and cuticle are important in host defense against Hessian fly

BACKGROUND

Wheat - Hessian fly interaction follows a typical gene-for-gene model. Hessian fly larvae die in wheat plants carrying an effective resistance gene, or thrive in susceptible plants that carry no effective resistance gene.

RESULTS

Gene sets affected by Hessian fly attack in resistant plants were found to be very different from those in susceptible plants. Differential expression of gene sets was associated with differential accumulation of intermediates in defense pathways. Our results indicated that resources were rapidly mobilized in resistant plants for defense, including extensive membrane remodeling and release of lipids, sugar catabolism, and amino acid transport and degradation. These resources were likely rapidly converted into defense molecules such as oxylipins; toxic proteins including cysteine proteases, inhibitors of digestive enzymes, and lectins; phenolics; and cell wall components. However, toxicity alone does not cause immediate lethality to Hessian fly larvae. Toxic defenses might slow down Hessian fly development and therefore give plants more time for other types of defense to become effective.

CONCLUSION

Our gene expression and metabolic profiling results suggested that remodeling and fortification of cell wall and cuticle by increased deposition of phenolics and enhanced cross-linking were likely to be crucial for insect mortality by depriving Hessian fly larvae of nutrients from host cells. The identification of a large number of genes that were differentially expressed at different time points during compatible and incompatible interactions also provided a foundation for further research on the molecular pathways that lead to wheat resistance and susceptibility to Hessian fly infestation.

Effects of disintegration on in vitro fermentation and conversion patterns of wheat aleurone in a metabolical colon model

This work aimed to elucidate the effect of wheat aleurone integrity on its fermentability, i.e., the formation of short-chain fatty acids (SCFA) and microbial phenolic metabolites, in an in vitro model using human faecal microbiota as an inoculum. The structure of aleurone was modified by mechanical (dry grinding) or enzymatic (xylanase with or without feruloyl esterase) treatments in order to increase its physical accessibility and degrade its complex cell-wall network. The ground aleurone (smaller particle size) produced slightly more SCFA than the native aleurone during the first 8 h but a similar amount at 24 h (102.5 and 101 mmol/L, respectively). Similar colonic metabolism of ferulic acid (FA) was observed for native and ground aleurone. The enzymatic treatments of aleurone allowed a high solubilization of arabinoxylan (up to 82%) and a high release of FA in its conjugated and free forms (up to 87%). The enzymatic disintegration of aleurone's structure led to a higher concentration and formation rate of the colonic metabolites of FA (especially phenylpropionic acids) but did not change significantly the formation of SCFA (81 mmol/L for enzyme treated versus 101 mmol/L for the native aleurone).

Deployment of the Burkholderia glumae type III secretion system as an efficient tool for translocating pathogen effectors to monocot cells

Genome sequences of plant fungal pathogens have enabled the identification of effectors that cooperatively modulate the cellular environment for successful fungal growth and suppress host defense. Identification and characterization of novel effector proteins are crucial for understanding pathogen virulence and host-plant defense mechanisms. Previous reports indicate that the Pseudomonas syringae pv. tomato DC3000 type III secretion system (T3SS) can be used to study how non-bacterial effectors manipulate dicot plant cell function using the effector detector vector (pEDV) system. Here we report a pEDV-based effector delivery system in which the T3SS of Burkholderia glumae, an emerging rice pathogen, is used to translocate the AVR-Pik and AVR-Pii effectors of the fungal pathogen Magnaporthe oryzae to rice cytoplasm. The translocated AVR-Pik and AVR-Pii showed avirulence activity when tested in rice cultivars containing the cognate R genes. AVR-Pik reduced and delayed the hypersensitive response triggered by B. glumae in the non-host plant Nicotiana benthamiana, indicative of an immunosuppressive virulence activity. AVR proteins fused with fluorescent protein and nuclear localization signal were delivered by B. glumae T3SS and observed in the nuclei of infected cells in rice, wheat, barley and N. benthamiana. Our bacterial T3SS-enabled eukaryotic effector delivery and subcellular localization assays provide a useful method for identifying and studying effector functions in monocot plants.

A differential redox regulation of the pathways metabolizing glyceraldehyde-3-phosphate tunes the production of reducing power in the cytosol of plant cells

Adaptation to aerobic life leads organisms to sense reactive oxygen species and use the signal for coordination of the entire metabolism. Glycolysis in plants is a particular network where specific steps, like oxidation of glyceraldehydes-3-phosphate (Ga3P), are critical in order for it to function. The triose-phosphate can be converted into 3-phosphoglycerate through the phosphorylating Ga3P dehydrogenase (Ga3PDHase, EC 1.2.1.12) producing ATP and NADH, or via the non-phosphorylating enzyme (np-Ga3PDHase; EC 1.2.1.9) generating NADPH. In this work we found redox regulation to be a posttranslational mechanism allowing the fine-tuning of the triose-phosphate fate. Both enzymes were inactivated after oxidation by reactive oxygen and nitrogen species. Kinetic studies determined that Ga3PDHase is marked (63-fold) more sensitive to oxidants than np-Ga3PDHase. Thioredoxin-h reverted the oxidation of both enzymes (although with differences between them), suggesting a physiological redox regulation. The results support a metabolic scenario where the cytosolic triose-phosphate dehydrogenases are regulated under changeable redox conditions. This would allow coordinate production of NADPH or ATP through glycolysis, with oxidative signals triggering reducing power synthesis in the cytosol. The NADPH increment would favor antioxidant responses to cope with the oxidative situation, while the thioredoxin system would positively feedback NADPH production by maintaining np-Ga3PDHase at its reduced active state.

Effective alleviation of aluminum phytotoxicity by manure-derived biochar

The alleviation of aluminum phytotoxicity to wheat plants in a hydroponic system through the amendment of biochar is investigated to explore the possibility of applying biochar in acidic soil amelioration. Biochar derived from cattle manure pyrolyzed at 400 °C (CM400) and the CM400 biochar washed with distilled-deionized water to remove alkalinity (WCM400) were prepared to determine the roles of the liming effect and adsorption during the alleviation of Al toxicity. Upon addition of 0.02% (W/V) CM400 to the exposure solution, the inhibition of plant growth by Al was significantly reduced while the toxic threshold was extended from 3 to 95 μmol/L Al(3+). Due to the biochar liming effect, the aluminum species were converted to Al(OH)(2+) and Al(OH)2(+) monomers, which were strongly adsorbed by biochar; furthermore, the highly toxic Al(3+) evolved to less toxic Al(OH)3 and Al(OH)4(-) species. Adsorption of Al by the biochar is dominated by surface complexation of the carboxyl groups with Al(OH)(2+)/Al(OH)2(+) rather than through electrostatic attraction of Al(3+) with negatively charged sites. Compared to the liming effect, the adsorption by biochar exhibited a sustainable effect on the alleviation of Al toxicity. Therefore, the biochar amendment appears to be a novel approach for aluminum detoxification in acidic soils.

Characterization of cell wall components of wheat straw following hydrothermal pretreatment and fractionation

Thermophysical pretreatment enhances the enzymatic hydrolysis of lignocellulose. However, its impact on cell wall chemistry is still poorly understood. This paper reports the effects of hydrothermal pretreatment on the degradation and alkali-extractability of wheat straw cell wall polymers. Pretreatment resulted in loss and/or solubilization of arabinoxylans (by 53%), ferulic and diferulic acids which are important cross-linking agents accompanied by concomitant increases in cellulose (up to 43%) and lignin (29%). The remaining water-insoluble hemicelluloses were more readily extractable in alkali and were reduced in molecular weight indicating substantial thermochemical depolymerization. They were also associated with smaller but significant amounts of (cellulose-derived) glucose. The alkali-insoluble residues consisted predominantly of cellulosic glucose and lignin and contained p-coumaric acid. The depolymerization of hemicelluloses, reduction in cinnamic acids and partial degradation of cellulose is likely to contribute significantly to the accessibility of cellulases during subsequent enzymolysis.

Organization of actin cytoskeleton during meiosis I in a wheat thermo-sensitive genic male sterile line

BS366 is a thermo-sensitive male sterile line of wheat (Triticum aestivum L.) for two-line hybrid breeding, which exhibits aberrant meiotic cytokinesis under low temperature. Through transcriptome analysis, a possible regulatory role for plant actin cytoskeleton was suggested. However, the organization of actin cytoskeleton in meiosis has been poorly understood so far. Here, fixed microsporocytes during meiosis were labeled with tetramethylrhodamine isothiocyanate-phalloidin and 4',6-diamidino-2-phenylindole. Quantities of fluorescent micrographs were captured using a confocal microscope, including the transient state from metaphase to telophase. We observed that actin filaments were abundant in typical kariokinetic spindle, central spindle (parallel microtubules or actin fibers between two separated chromosomes in anaphase), and phragmoplast. Interestingly, we identified the Chinese lantern-shaped actin phragmoplast in wheat meiosis for the first time. Under low temperature, phragmoplast actin filaments were chaotic and normal cell plate failed to form. These data provide new insights into the organization of actin filaments during male meiosis of plant and support a role of actin cytoskeleton in bringing about thermo-sensitive male sterility in wheat.

Metabolism of strobilurins by wheat cell suspension cultures

Strobilurin fungicides are a leading class of antifungal chemicals used today in agricultural applications. Although degradation of some strobilurin fungicides has been assessed in plant residues, little information has appeared in the literature concerning the rates of metabolism of these fungicides in plants. In this study, we explored plant metabolism of three strobilurin fungicides, azoxystrobin, kresoxim-methyl, and trifloxystrobin, using wheat cell suspension cultures. Trifloxystrobin and kresoxim-methyl were completely metabolized within 24 h, whereas the metabolism of azoxystrobin was relatively slow with half-lives up to 48 h depending on specific experimental conditions. Metabolic rates of these fungicides were affected by the amounts of compound and cells added to the media. Structural analysis of metabolites of trifloxystrobin and kresoxim-methyl by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance spectroscopy (NMR) indicated that trifloxystrobin was first demethylated followed by subsequent hydroxylation, whereas kresoxim-methyl was largely demethylated. In contrast, a number of minor metabolites of azoxystrobin were present suggesting a differential metabolism of strobilurins by wheat cells.