Regulation of cell wall remodeling in grapevine (Vitis vinifera L.) callus under individual mineral stress deficiency

Vineyard calcium sprays reduce the damage of postharvest grape berries by stimulating enzymatic antioxidant activity and pathogen defense genes, despite inhibiting phenolic synthesis

Calcium supplements have been increasingly used for decay prevention, sanitation and nutritional enrichment of fruits, as more environmentally friendly alternatives to fungicides. However, little is known on the effects of these supplements on grape berry biochemical and molecular properties during storage. In this study, we addressed the hypothesis that the application of calcium chloride (CaCl₂) in grapevines throughout the fruiting season reduces damage (and decay) of postharvest grape berries, through several biochemical and transcriptional modifications in sugar transport, secondary metabolism, antioxidant activity, cell wall organization and pathogen defense. Results showed that calcium (Ca) treatments in cv. "Vinhão" vines increased fruit Ca content and significantly decreased fruit damage by 60%, 10-d after storage at 4 °C. Grape berries from Ca-treated vines displayed lower levels of total phenolics and anthocyanins, compared to control fruits, corroborating the downregulation of PAL1 and STS which resulted in decreased non-enzymatic antioxidant capacity estimated by FRAP assay. In contrast, a strong upregulation of CAT1, ASPX1, ASPX3, GLPX1, CSD3 and CSD6 encoding antioxidant enzymes was observed. Accordingly, catalase enzyme activity was stimulated, significantly reducing hydrogen peroxide (H₂O₂) levels by 36%. The overexpression of the cell wall and pathogen defense genes PME, PGIP, PIN and PR1 likely contributed to the reduction in fruit rot. This work suggested that preharvest Ca treatment is an efficient agronomical strategy that prolongs the shelf life of grape berries through modifications at molecular and biochemical levels, bringing further insight on the benefits and drawbacks of preharvest Ca applications on postharvest fruit quality attributes.

The relationship between fluoride accumulation in tea plant and changes in leaf cell wall structure and composition under different fluoride conditions

Tea plant is capable of hyper-accumulating fluoride (F) in leaves, suggesting drinking tea may cause excessive F intake in our body and threaten the health. This study investigated the changes in the structure, composition, and F content in the leaf cell wall of the tea (Camellia sinensis) under different F conditions to demonstrate the role of cell wall in F enrichment in tea plants. The cell wall was shown as the main part for F accumulation (67%-92%), with most of F distributed in the pectin fraction (56%-71%). With increasing F concentration, a significant increase (p < 0.05) was observed in the F content of cell wall and its components, the level of cell wall metal ions (i.e. Cu, Mg, Zn, Al, Ca, Ba, Mn), as well as the content of total cell wall materials, cellulose, and pectin. Meanwhile, the level of Cu, Mg, Zn, pectin, and cellulose was significantly positively correlated with the F content in the leaf cell wall. F addition was shown to increase the fluorescence intensity of LM19 and 2F4 antibody-labeled low-methylesterified homogalacturonans (HGs), while decrease LM20-labeled high-methylesterified HGs, coupled with an increase in the activity and gene expression of pectin methyl esterases (PMEs) in tea leaves. All these results suggest that F addition can increase pectin content and demethylesterification, leading to increased absorption of metal cations and chelation of F in the cell wall through the action of metal ions.

Quantitative proteomics analysis of tomato growth inhibition by ammonium nitrogen

As a single nitrogen source, ammonium (NH₄⁺) can inhibit the growth of plants, especially when applied in excess. Tandem mass tag (TMT) quantitative proteomics technology was employed in the current study to explore and analyze the mechanisms of ammonium-induced inhibition. F₁ tomato (Lycopersicon esculentum Mill) was used in this study. Seedlings at the four leaf-stages grown in a greenhouse were irrigated using nutrient solution with NH₄⁺-N as single nitrogen source (15 mmol L^-1, single NO₃^--N as control) for 5 weeks. Compared to the control, the root biomass of NH₄⁺-N-treated seedlings decreased by 50%. In addition, NH₄⁺ content in roots was 2.83-fold increased and soluble sugar and protein contents were increased. However, the starch content did not change significantly. The activities of glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamate dehydrogenase (GDH), which are involved in ammonium assimilation, were increased, and glutamine (Gln) content was also increased. However, glutamate (Glu) content, which is important for amino transfer, did not significantly increase. Ammonium assimilation was inhibited. Root quantitative proteomics showed that carbonic anhydrase Q5NE21 was significantly downregulated. Although K4BPV5 and K4D9J3 proteins, which improve ammonium assimilation, were upregulated, ammonium assimilation was limited. In addition, NH₄⁺ accumulated, which is likely due to Q5NE21 downregulation. Meanwhile, cell wall metabolism related to phenylpropanoid biosynthesis was altered due to the accumulation of NH₄⁺ levels. Subsequently, tomato root growth was inhibited.

Vineyard calcium sprays induce changes in grape berry skin, firmness, cell wall composition and expression of cell wall-related genes

Having a central role in cell wall pectin cross-linking, calcium has been increasingly used as supplement to promote fruit firmness and extended shelf-life. However, the molecular rearrangements associated to increased fruit robustness are still a matter of debate. In this study, mechanical, histochemical and molecular assays were conducted to understand the mechanisms underlying the effects of Ca in fruit physical properties. In a two-year field trial, grapevines were sprayed with exogenous CaCl₂ throughout the fruiting season. Results showed an increase in berry Ca concentration at harvest, associated to increased fruit consistency and skin resistance. Scanning electron microscopy showed that fruits from Ca-treated plants had smoother skin surfaces than control fruits, and that microcracks encircling the lenticels were less prominent. Histochemistry assays suggested higher deposition of pectin-like material in skin cell walls in grapes from Ca-treated vines, but no evident modifications in cellulose content were observed. Accordingly, the expression of cellulose synthase family gene CesA3 was not affected by exogenous Ca, while polygalacturonase-encoding genes PG1 and PG2 were downregulated, together with EXP6 belonging to expansin family, and CER9 and CYP15 involved in cuticle biosynthesis. These results suggested that Ca acts by inhibiting pectin degradation and cell wall loosening, while remodeling cuticle structure.

The source of inorganic nitrogen has distinct effects on cell wall composition in Brachypodium distachyon

Plants have evolved different strategies to utilize various forms of nitrogen (N) from the environment. While regulation of plant growth and development in response to application of inorganic N forms has been characterized, our knowledge about the effect on cell wall structure and composition is quite limited. In this study, we analysed cell walls of Brachypodium distachyon supplied with three types of inorganic N (NH4NO3, NO3-, or NH4+). Cell wall profiles showed distinct alterations in both the quantity and structures of individual polymers. Nitrate stimulated cellulose, but inhibited lignin deposition at the heading growth stage. On the other hand, ammonium supply resulted in higher concentration of mixed linkage glucans. In addition, the chemical structure of pectins and hemicelluloses was strongly influenced by the form of N. Supply of only NO3- led to alteration in xylan substitution and to lower esterification of homogalacturonan. We conclude that the physiological response to absorption of different inorganic N forms includes pleotropic remodelling of type II cell walls.

Map-Based Functional Analysis of the GhNLP Genes Reveals Their Roles in Enhancing Tolerance to N-Deficiency in Cotton

Nitrogen is a key macronutrient needed by plants to boost their production, but the development of cotton genotypes through conventional approaches has hit a bottleneck due to the narrow genetic base of the elite cotton cultivars, due to intensive selection and inbreeding. Based on our previous research, in which the BC₂F₂ generations developed from two upland cotton genotypes, an abiotic stress-tolerant genotype, G. tomentosum (donor parent) and a highly-susceptible, and a highly-susceptible, but very productive, G. hirsutum (recurrent parent), were profiled under drought stress conditions. The phenotypic and the genotypic data generated through genotyping by sequencing (GBS) were integrated to map drought-tolerant quantitative trait loci (QTLs). Within the stable QTLs region for the various drought tolerance traits, a nodule-inception-like protein (NLP) gene was identified. We performed a phylogenetic analysis of the NLP proteins, mapped their chromosomal positions, intron-exon structures and conducted ds/dn analysis, which showed that most NLP genes underwent negative or purifying selection. Moreover, the functions of one of the highly upregulated genes, Gh_A05G3286 (Gh NLP5), were evaluated using the virus gene silencing (VIGS) mechanism. A total of 226 proteins encoded by the NLP genes were identified, with 105, 61, and 60 in Gossypium hirsutum, G. raimondii, and G. arboreum, respectively. Comprehensive Insilico analysis revealed that the proteins encoded by the NLP genes had varying molecular weights, protein lengths, isoelectric points (pI), and grand hydropathy values (GRAVY). The GRAVY values ranged from a negative one to zero, showing that proteins were hydrophilic. Moreover, various cis-regulatory elements that are the binding sites for stress-associated transcription factors were found in the promoters of various NLP genes. In addition, many miRNAs were predicted to target NLP genes, notably miR167a, miR167b, miR160, and miR167 that were previously shown to target five NAC genes, including NAC1 and CUC1, under N-limited conditions. The real-time quantitative polymerase chain reaction (RT-qPCR) analysis, revealed that five genes, Gh_D02G2018, Gh_A12G0439, Gh_A03G0493, Gh_A03G1178, and Gh_A05G3286 were significantly upregulated and perhaps could be the key NLP genes regulating plant response under N-limited conditions. Furthermore, the knockdown of the Gh_A05G3286 (GhNLP5) gene by virus-induced silencing (VIGS) significantly reduced the ability of these plants to the knockdown of the Gh_A05G3286 (GhNLP5) gene by virus-induced gene silencing (VIGS) significantly reduced the ability of the VIGS-plants to tolerate N-limited conditions compared to the wild types (WT). The VIGS-plants registered lower chlorophyll content, fresh shoot biomass, and fresh root biomass, addition to higher levels of malondialdehyde (MDA) and significantly reduced levels of proline, and superoxide dismutase (SOD) compared to the WT under N-limited conditions. Subsequently, the expression levels of the Nitrogen-stress responsive genes, GhTap46, GhRPL18A, and GhKLU were shown to be significantly downregulated in VIGS-plants compared to their WT under N-limited conditions. The downregulation of the nitrogen-stress responsive genes provided evidence that the silenced gene had an integral role in enhancing cotton plant tolerance to N-limited conditions.

Transcriptomic analysis reveals adaptive strategies to chronic low nitrogen in Tibetan wild barley

BACKGROUND

Development of crop cultivars with high low nitrogen (LN) tolerance or nitrogen use efficiency (NUE) is imperative for sustainable agriculture development. Tibetan wild barley is rich in genetic diversity and may provide elite genes for LN tolerance improvement. Little has been known about transcriptional responses of the wild barley to chronic LN stress.

RESULTS

In this study, transcriptomic profiling of two Tibetan wild barley genotypes, LN- tolerant XZ149 and LN-sensitive XZ56 has been conducted using RNA-Seq to reveal the genotypic difference in response to chronic LN stress. A total of 520 differentially expressed genes (DEGs) were identified in the two genotypes at 12 d after LN stress, and these DEGs could be mainly mapped to 49 metabolism pathways. Chronic LN stress lead to genotype-dependent responses, and the responsive pattern in favor of root growth and stress tolerance may be the possible mechanisms of the higher chronic LN tolerance in XZ149.

CONCLUSION

There was a distinct difference in transcriptional profiling between the two wild barley genotypes in response to chronic LN stress. The identified new candidate genes related to LN tolerance may cast a light on the development of cultivars with LN tolerance.

Abiotic Stresses: General Defenses of Land Plants and Chances for Engineering Multistress Tolerance

Abiotic stresses, such as low or high temperature, deficient or excessive water, high salinity, heavy metals, and ultraviolet radiation, are hostile to plant growth and development, leading to great crop yield penalty worldwide. It is getting imperative to equip crops with multistress tolerance to relieve the pressure of environmental changes and to meet the demand of population growth, as different abiotic stresses usually arise together in the field. The feasibility is raised as land plants actually have established more generalized defenses against abiotic stresses, including the cuticle outside plants, together with unsaturated fatty acids, reactive species scavengers, molecular chaperones, and compatible solutes inside cells. In stress response, they are orchestrated by a complex regulatory network involving upstream signaling molecules including stress hormones, reactive oxygen species, gasotransmitters, polyamines, phytochromes, and calcium, as well as downstream gene regulation factors, particularly transcription factors. In this review, we aimed at presenting an overview of these defensive systems and the regulatory network, with an eye to their practical potential via genetic engineering and/or exogenous application.

Tubulins, rhythms and cell walls in poplar leaves: it's all in the timing

Plant cell walls exhibit architectural and compositional changes throughout their development and in response to external cues. While tubulins are involved in cell wall biogenesis, much remains unknown about the scope of their involvement during the orchestration of this resource-demanding process. A transgenic approach coupled with cell wall compositional analysis, RNA-seq and mining of publicly available diurnal gene expression data was used to assess the involvement of tubulins in poplar leaf cell wall biogenesis. Leaf cell walls of transgenic poplar lines with constitutive overexpression of α-tubulin (TUA) exhibited an increased abundance of homogalacturonan, along with a reduction in xylose. These changes were traced to altered expression of UDP-glucuronic acid decarboxylase (GADC) in the transgenic leaves. A model is postulated by which altered diurnal control of TUA through its constitutive overexpression led to a metabolic tradeoff affecting cellular utilization of GADC substrate UDP-glucuronic acid. While there were no effects on cellulose, hemicellulose or lignin abundance, subtle effects on hemicellulose composition and associated gene expression were noted. In addition, expression and enzymatic activity of pectin methylesterase (PME) decreased in the transgenic leaves. The change is discussed in a context of increased levels of PME substrate homogalacturonan, slow stomatal kinetics and the fate of PME product methanol. Since stomatal opening and closing depend on fundamentally contrasting microtubule dynamics, the slowing of both processes in the transgenic lines as previously reported appears to be directly related to underlying cell wall compositional changes that were caused by tubulin manipulation.

How the Depletion in Mineral Major Elements Affects Grapevine (Vitis vinifera L.) Primary Cell Wall

The noteworthy fine remodeling that plant cell walls (CWs) undergo to adapt to developmental, physiological and environmental cues and the observation that its composition and dynamics differ between species represents an opportunity to couple crop species agronomic studies with research on CW modifications. Vitis vinifera is one of the most important crops from an economic point-of-view due to the high value of the fruit, predominantly for winemaking. The availability of some information related to this species' CWs allows researching its responses to imposed conditions that affect the plant's development. Mineral deficiency, in particular nitrogen, phosphorus, potassium and sulfur, strongly affects plant metabolism, reducing both growth and crop yield. Despite the importance of mineral nutrition in development, its influence on CW synthesis and modifications is still insufficiently documented. Addressing this knowledge gap, V. vinifera experimental models were used to study CW responses to imposed mineral depletion in unorganized (callus) and organized (shoots) tissues. The discussion of the obtained results is the main focus of this review. Callus and shoots submitted to mineral restriction are impaired in specific CW components, predominantly cellulose. Reorganization on structure and deposition of several other polymers, in particular the degree and pattern of pectin methyl-esterification and the amount of xyloglucan (XyG), arabinan and extensin, is also observed. In view of recently proposed CW models that consider biomechanical hotspots and direct linkages between pectins and XyG/cellulose, the outcome of these modifications in explaining maintenance of CW integrity through compensatory stiffening can be debated. Nutrient stresses do not affect evenly all tissues with undifferentiated callus tissues showing more pronounced responses, followed by shoot mature internodes, and then newly formed internodes. The impact of nitrogen depletion leads to more noticeable responses, supporting this nutrient's primary role in plant development and metabolism. The consequential compensatory mechanisms highlight the pivotal role of CW in rearranging under environmental stresses.

Nitrate Uptake Affects Cell Wall Synthesis and Modeling

Nowadays, the relationship(s) about N assimilation and cell wall remodeling in plants remains generally unclear. Enzymes involved in cell wall synthesis/modification, and nitrogen transporters play a critical role in plant growth, differentiation, and response to external stimuli. In this review, a co-expression analysis of nitrate and ammonium transporters of Arabidopsis thaliana was performed in order to explore the functional connection of these proteins with cell-wall related enzymes. This approach highlighted a strict relationship between inorganic nitrogen transporters and cell wall formation, identifying a number of co-expressed remodeling enzymes. The enzymes involved in pectin and xyloglucan synthesis resulted particularly co-regulated together with nitrate carriers, suggesting a connection between nitrate assimilation and cell wall growth regulation. Major Facilitator Carriers, and one chloride channel, are similarly co-expressed with pectin lyase, pectinacetylesterase, and cellulose synthase. Contrarily, ammonium transporters show little or no connection with those genes involved in cell wall synthesis. Different aspects related to plant development, embryogenesis, and abiotic stress response will be discussed, given the importance in plant growth of cell wall synthesis and nitrate uptake. Intriguingly, the improvement of abiotic stress tolerance in crops concerns both these processes indicating the importance in sensing the environmental constraints and mediating a response. These evaluations could help to identify candidate genes for breeding purposes.

Immunolocalization of cell wall polymers in grapevine (Vitis vinifera) internodes under nitrogen, phosphorus or sulfur deficiency

The impact on cell wall (CW) of the deficiency in nitrogen (-N), phosphorus (-P) or sulphur (-S), known to impair essential metabolic pathways, was investigated in the economically important fruit species Vitis vinifera L. Using cuttings as an experimental model a reduction in total internode number and altered xylem shape was observed. Under -N an increased internode length was also seen. CW composition, visualised after staining with calcofluor white, Toluidine blue and ruthenium red, showed decreased cellulose in all stresses and increased pectin content in recently formed internodes under -N compared to the control. Using CW-epitope specific monoclonal antibodies (mAbs), lower amounts of extensins incorporated in the wall were also observed under -N and -P conditions. Conversely, increased pectins with a low degree of methyl-esterification and richer in long linear 1,5-arabinan rhamnogalacturonan-I (RG-I) side chains were observed under -N and -P in mature internodes which, in the former condition, were able to form dimeric association through calcium ions. -N was the only condition in which 1,5-arabinan branched RG-I content was not altered, as -P and -S older internodes showed, respectively, lower and higher amounts of this polymer. Higher xyloglucan content in older internodes was also observed under -N. The results suggest that impairments of specific CW components led to changes in the deposition of other polymers to promote stiffening of the CW. The unchanged extensin amount observed under -S may contribute to attenuating the effects on the CW integrity caused by this stress. Our work showed that, in organized V. vinifera tissues, modifications in a given CW component can be compensated by synthesis of different polymers and/or alternative linking between polymers. The results also pinpoint different strategies at the CW level to overcome mineral stress depending on how essential they are to cell growth and plant development.