Exploring the genetic landscape of nitrogen uptake in durum wheat: genome-wide characterization and expression profiling of NPF and NRT2 gene families

Nitrate uptake by plants primarily relies on two gene families: Nitrate transporter 1/peptide transporter (NPF) and Nitrate transporter 2 (NRT2). Here, we extensively characterized the NPF and NRT2 families in the durum wheat genome, revealing 211 NPF and 20 NRT2 genes. The two families share many Cis Regulatory Elements (CREs) and Transcription Factor binding sites, highlighting a partially overlapping regulatory system and suggesting a coordinated response for nitrate transport and utilization. Analyzing RNA-seq data from 9 tissues and 20 cultivars, we explored expression profiles and co-expression relationships of both gene families. We observed a strong correlation between nucleotide variation and gene expression within the NRT2 gene family, implicating a shared selection mechanism operating on both coding and regulatory regions. Furthermore, NPF genes showed highly tissue-specific expression profiles, while NRT2s were mainly divided in two co-expression modules, one expressed in roots (NAR2/NRT3 dependent) and the other induced in anthers and/ovaries during maturation. Our evidences confirmed that the majority of these genes were retained after small-scale duplication events, suggesting a neo- or sub-functionalization of many NPFs and NRT2s. Altogether, these findings indicate that the expansion of these gene families in durum wheat could provide valuable genetic variability useful to identify NUE-related and candidate genes for future breeding programs in the context of low-impact and sustainable agriculture.

Nitrogen fertilization and arbuscular mycorrhizal fungi do not mitigate the adverse effects of soil contamination with polypropylene microfibers on maize growth

Soil contamination with microplastics may adversely affect soil properties and functions and consequently crop productivity. In this study, we wanted to verify whether the adverse effects of microplastics in the soil on maize plants (Zea mays L.) are due to a reduction in nitrogen (N) availability and a reduced capacity to establish symbiotic relationships with arbuscular mycorrhizal (AM) fungi. To do this, we performed a pot experiment in which a clayey soil was exposed to two environmentally relevant concentrations of polypropylene (PP; one of the most used plastic materials) microfibers (0.4% and 0.8% w/w) with or without the addition of N fertilizer and with or without inoculation with AM fungi. The experiment began after the soil had been incubated at 23 °C for 5 months. Soil contamination with PP considerably reduced maize root and shoot biomass, leaf area, N uptake, and N content in tissue. The adverse effects increased with the concentration of PP in the soil. Adding N to the soil did not alleviate the detrimental effects of PP on plant growth, which suggests that other factors besides N availability played a major role. Similarly, although the presence of PP did not inhibit root colonization by AM fungi (no differences were observed for this trait between the uncontaminated and PP-contaminated soils), the addition of the fungal inoculum to the soil failed to mitigate the negative impact of PP on maize growth. Quite the opposite: mycorrhization further reduced maize root biomass accumulation. Undoubtedly, much research remains to be done to shed light on the mechanisms involved in determining plant behavior in microplastic-contaminated soils, which are most likely complex. This research is a priority given the magnitude of this contamination and its potential implications for human and environmental health.

Transcriptome changes induced by Arbuscular mycorrhizal symbiosis in leaves of durum wheat (Triticum durum Desf.) promote higher salt tolerance

The salinity of soil is a relevant environmental problem around the world, with climate change raising its relevance, particularly in arid and semiarid areas. Arbuscular Mycorrhizal Fungi (AMF) positively affect plant growth and health by mitigating biotic and abiotic stresses, including salt stress. The mechanisms through which these benefits manifest are, however, still unclear. This work aimed to identify key genes involved in the response to salt stress induced by AMF using RNA-Seq analysis on durum wheat (Triticum turgidum L. subsp. durum Desf. Husn.). Five hundred sixty-three differentially expressed genes (DEGs), many of which involved in pathways related to plant stress responses, were identified. The expression of genes involved in trehalose metabolism, RNA processing, vesicle trafficking, cell wall organization, and signal transduction was significantly enhanced by the AMF symbiosis. A downregulation of genes involved in both enzymatic and non-enzymatic oxidative stress responses as well as amino acids, lipids, and carbohydrates metabolisms was also detected, suggesting a lower oxidative stress condition in the AMF inoculated plants. Interestingly, many transcription factor families, including WRKY, NAC, and MYB, already known for their key role in plant abiotic stress response, were found differentially expressed between treatments. This study provides valuable insights on AMF-induced gene expression modulation and the beneficial effects of plant-AMF interaction in durum wheat under salt stress.

Early sowing can boost grain production by reducing weed infestation in organic no-till wheat

BACKGROUND

Conservative tillage techniques have several agro-ecological benefits for organic farming. The application of these techniques, however, can create quite a few challenges due to the increased weed competition. Here, we report the results of an organic field experiment in which the responses of wheat and weeds to no tillage (NT) were evaluated compared with conventional tillage (CT). We also tested the hypothesis that, under NT, moving up the sowing date, compared with using the ordinary sowing date for the study area, can result in increased competitiveness of the crop against weeds. Two wheat genotypes, a modern variety and an ancient landrace, were tested.

RESULTS

Substantial reductions in grain yield and protein content were observed in wheat under NT than under CT when the ordinary sowing date was used. This was mainly due to the considerable increase in weed biomass under NT. The tillage system also altered the composition of weed flora, with some species favored under NT and others under CT. In general, early sowing mitigated the detrimental effect of NT on yield. The two genotypes responded differently to the treatments. The early sowing in the modern variety reduced but did not eliminate the advantages of CT over NT, whereas no appreciable differences in grain yield were observed between CT and NT in the landrace.

CONCLUSION

Our results show clearly that, under organic management, using NT alone as a substitute for CT is not agronomically feasible. Moving up the sowing date and using a competitive genotype can help mitigate the negative effects of NT, but surely a more effective application of NT could be achieved by acting simultaneously on other factors of the cropping management system (e.g. crop rotation, fertilization strategy, type of seeder). © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Addition of high C:N crop residues to a P-limited substrate constrains the benefits of arbuscular mycorrhizal symbiosis for wheat P and N nutrition

Many aspects concerning the role of arbuscular mycorrhizal (AM) fungi in plant nutrient uptake from organic sources remain unclear. Here, we investigated the contribution of AM symbiosis to N and P uptake by durum wheat after the addition of a high C:N biomass to a P-limited soil. Plants were grown in pots in the presence or absence of a multispecies AM inoculum, with (Org) or without (Ctr) the addition of 15N-labelled organic matter (OM). A further treatment, in which 15N was applied in mineral form (Ctr+N) in the same amount as that supplied in the Org treatment, was also included. Inoculation with AM had positive effects on plant growth in both control treatments (Ctr and Ctr+N), mainly linked to an increase in plant P uptake. The addition of OM, increasing the P available in the soil for the plants, resulted in a marked decrease in the contribution of AM symbiosis to plant growth and nutrient uptake, although the percentage of mycorrhization was higher in the Org treatment than in the controls. In addition, mycorrhization drastically reduced the recovery of 15N from the OM added to the soil whereas it slightly increased the N recovery from the mineral fertiliser. This suggests that plants and AM fungi probably exert a differential competition for different sources of N available in the soil. On the whole, our results provide a contribution to a better understanding of the conditions under which AM fungi can play an effective role in mitigating the negative effects of nutritional stresses in plants.

Influence of grain quality, semolinas and baker's yeast on bread made from old landraces and modern genotypes of Sicilian durum wheat

Several studies showed that products made with ancient wheat genotypes have beneficial health properties compared to those obtained with modern wheat varieties, even though the mechanisms responsible for the positive effects are not clear. Ancient durum wheat genotypes are being currently used for the production of pasta, bread and other typical bakery products but the consumption is strictly local. In this work 15 genotypes of Triticum turgidum subsp. durum, including 10 ancient and 5 modern, were characterized for their technological traits through the determination of different parameters: protein content, dry gluten, gluten index, yellow index, ash, P/L, W and G. In addition, the baking aptitude of all genotypes was evaluated. All semolinas were subjected to leavening by commercial baker's yeast and the experimental breads were subjected to the qualitative characterization (weight loss, height, firmness, colour, volatile organic compounds, image and sensory analysis). The results obtained showed that protein content of grains and semolinas was higher in ancient rather than modern genotypes. Dry gluten ranged from 6.7% of the modern variety Simeto to 13.6% of the ancient genotype Scorsonera. Great differences were found for the yellow index which reached the highest value in Saragolla variety. The P/L and W ratios were significantly higher for the modern genotypes. On average, weight loss was about 14 g, while bread height varied significantly between the trials. Bread consistency varied between 12.6 and 31.3 N. Differences were observed for the yellow of the crumb (higher for modern genotypes) and for the redness of the crust (higher for ancient genotypes). The sensory evaluation displayed a high variability among the breads from the 10 ancient genotypes, while the control breads received scores closed to those of the modern genotypes. This study revealed that the modern durum wheat varieties showed a certain uniformity of behaviour, while the ancient genotypes exhibited a great variability of the final attributes of breads.

Relationship between Seed Morphological Traits and Ash and Mineral Distribution along the Kernel Using Debranning in Durum Wheats from Different Geographic Sites

Debranning was applied to durum wheat to the study the relationship between kernel shape and size, and ash and mineral distribution having implications for semolina yield. To this aim four durum wheat genotypes carried out over three environments were selected to determine the morphological and yield traits as well as the distribution along the kernel of the ash, macro- (Na, K, P, Ca, and Mg), and micro-elements (Mn, Fe, Cu, Zn, and Mo). A descendent ash gradient within the kernel reflects the decreases in the minerals that occurred during debranning. Perciasacchi with high seed weight (TKW) and greater thickness followed by Cappelli showed a more uniform distribution of ash content along the kernels. High r Pearson coefficient (p < 0.01) showed an inverse relationship between thickness and ash decay. Since thickness was strongly affected by the genotype, it could represent a useful trait for breeding programs to predict the milling quality.

Nitrogen Type and Availability Drive Mycorrhizal Effects on Wheat Performance, Nitrogen Uptake and Recovery, and Production Sustainability

Plant performance is strongly dependent on nitrogen (N), and thus increasing N nutrition is of great relevance for the productivity of agroecosystems. The effects of arbuscular mycorrhizal (AM) fungi on plant N acquisition are debated because contradictory results have been reported. Using 15N-labeled fertilizers as a tracer, we evaluated the effects of AM fungi on N uptake and recovery from mineral or organic sources in durum wheat. Under sufficient N availability, AM fungi had no effects on plant biomass but increased N concentrations in plant tissue, plant N uptake, and total N recovered from the fertilizer. In N-deficient soil, AM fungi led to decreased aboveground biomass, which suggests that plants and AM fungi may have competed for N. When the organic source had a low C:N ratio, AM fungi favored both plant N uptake and N recovery. In contrast, when the organic source had a high C:N ratio, a clear reduction in N recovery from the fertilizer was observed. Overall, the results indicate an active role of arbuscular mycorrhizae in favoring plant N-related traits when N is not a limiting factor and show that these fungi help in N recovery from the fertilizer. These results hold great potential for increasing the sustainability of durum wheat production.

Soil inoculation with symbiotic microorganisms promotes plant growth and nutrient transporter genes expression in durum wheat

In a field experiment conducted in a Mediterranean area of inner Sicily, durum wheat was inoculated with plant growth-promoting rhizobacteria (PGPR), with arbuscular mycorrhizal fungi (AMF), or with both to evaluate their effects on nutrient uptake, plant growth, and the expression of key transporter genes involved in nitrogen (N) and phosphorus (P) uptake. These biotic associations were studied under either low N availability (unfertilized plots) and supplying the soil with an easily mineralizable organic fertilizer. Regardless of N fertilization, at the tillering stage, inoculation with AMF alone or in combination with PGPR increased the aboveground biomass yield compared to the uninoculated control. Inoculation with PGPR enhanced the aboveground biomass yield compared to the control, but only when N fertilizer was added. At the heading stage, inoculation with all microorganisms increased the aboveground biomass and N. Inoculation with PGPR and AMF+PGPR resulted in significantly higher aboveground P compared to the control and inoculation with AMF only when organic N was applied. The role of microbe inoculation in N uptake was elucidated by the expression of nitrate transporter genes. NRT1.1, NRT2, and NAR2.2 were significantly upregulated by inoculation with AMF and AMF+PGPR in the absence of organic N. A significant down-regulation of the same genes was observed when organic N was added. The ammonium (NH4 (+)) transporter genes AMT1.2 showed an expression pattern similar to that of the NO3 (-) transporters. Finally, in the absence of organic N, the transcript abundance of P transporters Pht1 and PT2-1 was increased by inoculation with AMF+PGPR, and inoculation with AMF upregulated Pht2 compared to the uninoculated control. These results indicate the soil inoculation with AMF and PGPR (alone or in combination) as a valuable option for farmers to improve yield, nutrient uptake, and the sustainability of the agro-ecosystem.

Nitrogen uptake and nitrogen fertilizer recovery in old and modern wheat genotypes grown in the presence or absence of interspecific competition

Choosing genotypes with a high capacity for taking up nitrogen (N) from the soil and the ability to efficiently compete with weeds for this nutrient is essential to increasing the sustainability of cropping systems that are less dependent on auxiliary inputs. This research aimed to verify whether differences exist in N uptake and N fertilizer recovery capacity among wheat genotypes and, if so, whether these differences are related to a different competitive ability against weeds of wheat genotypes. To this end, 12 genotypes, varying widely in morphological traits and year of release, were grown in the presence or absence of interspecific competition (using Avena sativa L. as a surrogate weed). Isotopic tracer (15)N was used to measure the fertilizer N uptake efficiencies of the wheat genotypes and weed. A field experiment, a split-plot design with four replications, was conducted during two consecutive growing seasons in a typical Mediterranean environment. In the absence of interspecific competition, few differences in either total N uptake (range: 98-112 kg N ha(-1)) or the (15)N fertilizer recovery fraction (range: 30.0-36.7%) were observed among the wheat genotypes. The presence of competition, compared to competitor-free conditions, resulted in reductions in grain yield (49%), total N uptake (29%), and an (15)N fertilizer recovery fraction (32%) that were on average markedly higher in modern varieties than in old ones. Both biomass and grain reductions were strongly related to the biomass of the competitor (correlation coefficients > 0.95), which ranged from 135 to 573 g m(-2). Variations in both grain and biomass yield due to interspecific competition were significantly correlated with percentage of soil cover and leaf area at tillering, plant height at heading, and total N uptake, thus highlighting that the ability to take up N from the soil played a certain role in determining the different competitive abilities against weed of the genotypes.