Kinetics of glyphosate and aminomethylphosphonic acid sorption onto montmorillonite clays in soil and their translocation to genetically modified corn.

The co-occurrence of glyphosate (GLP) and aminomethylphosphonic acid (AMPA) in contaminated water, soil, sediment and plants is a cause for concern due to potential threats to the ecosystem and human health. A major route of exposure is through contact with contaminated soil and consumption of crops containing GLP and AMPA residues. However, clay-based sorption strategies for mixtures of GLP and AMPA in soil, plants and garden produce have been very limited. In this study, in vitro soil and in vivo genetically modified corn models were used to establish the proof of concept that the inclusion of clay sorbents in contaminated soils will reduce the bioavailability of GLP and AMPA in soils and their adverse effects on plant growth. Effects of chemical concentration (1-10 mg/kg), sorbent dose (0.5%-3% in soil and 0.5%-1% in plants) and duration (up to 28 days) on sorption kinetics were studied. The time course results showed a continuous GLP degradation to AMPA. The inclusion of calcium montmorillonite (CM) and acid processed montmorillonite (APM) clays at all doses significantly and consistently reduced the bioavailability of both chemicals from soils to plant roots and leaves in a dose- and time-dependent manner without detectable dissociation. Plants treated with 0.5% and 1% APM inclusion showed the highest growth rate (p ≤ 0.05) and lowest chemical bioavailability with up to 76% reduction in roots and 57% reduction in leaves. Results indicated that montmorillonite clays could be added as soil supplements to reduce hazardous mixtures of GLP and AMPA in soils and plants.

Leaf surface features of maize cultivars and response to foliar phosphorus application: effect of leaf stage and plant phosphorus status.

Soil phosphorus (P) application is the most common fertilisation technique but may involve constraints due to chemical fixation and microbial immobilisation. Furthermore, excessive P fertilisation leads to P runoff into water bodies, threatening ecosystems, so targeted foliar P fertilisation is an interesting alternative. This study aimed to determine the importance of leaf surface characteristics for foliar P uptake in P-deficient maize (Zea mays L.). The leaf surface of four maize cultivars was characterised by electron microscopy, Fourier transform infrared spectroscopy and contact angle measurements. Uptake of foliar-applied P by maize cultivars was estimated, measuring also leaf photosynthetic rates after foliar P spraying. Plants of cultivar P7948 were found to be wettable from the 4th leaf in acropetal direction, whereas other cultivars were unwettable until the 6th leaf had developed. Minor variations in stomatal number and cuticle composition were recorded, but no differences in foliar P absorption were observed between cultivars. Nevertheless, cultivars showed variation in the improvement of photosynthetic capacity following foliar P application. Phosphorus deficiency resulted in ultrastructural disorganisation of mesophyll cells and chloroplasts, which impaired photosynthetic performance, yet there was no effect on stomatal frequency and leaf wettability. This study provides new insights into the influence of P deficiency and cultivar on leaf surface characteristics, foliar P uptake and its effect on physiological processes. Understanding the relationships between leaf characteristics and P uptake allows a more targeted evaluation of foliar P fertilisation as an application technique and contributes to the understanding of foliar uptake mechanisms.

Maize sterility gene DRP1 encodes a desiccation-related protein that is critical for Ubisch bodies and pollen exine development.

Desiccation tolerance is a remarkable feature of pollen, seeds, and resurrection-type plants. Exposure to desiccation stress can cause sporophytic defects, resulting in male sterility. Here, we report the novel maize sterility gene DRP1 (Desiccation-Related Protein 1), which was identified by bulked-segregant analysis sequencing and encodes a desiccation-related protein. Loss of function of DRP1 results in abnormal Ubisch bodies, defective tectum of the pollen exine, and complete male sterility. Our results suggest that DRP1 may facilitate anther dehydration to maintain appropriate water status. DRP1 is a secretory protein that is specifically expressed in the tapetum and microspore from the tetrad to the uninucleate microspore stage. Differentially expressed genes in drp1 are enriched in Gene Ontology terms for pollen exine formation, polysaccharide catabolic process, extracellular region, and response to heat. In addition, DRP1 is a target of selection that appears to have played an important role in the spread of maize from tropical/subtropical to temperate regions. Taken together, our results suggest that DRP1 encodes a desiccation-related protein whose loss of function causes male sterility. Our findings provide a potential genetic resource that may be used to design crops for heterosis utilization.

Nutrition vs association: plant defenses are altered by arbuscular mycorrhizal fungi association not by nutritional provisioning alone.

BACKGROUND: While it is known that arbuscular mycorrhizal fungi (AMF) can improve nutrient acquisition and herbivore resistance in crops, the mechanisms by which AMF influence plant defense remain unknown. Plants respond to herbivory with a cascade of gene expression and phytochemical biosynthesis. Given that the production of defensive phytochemicals requires nutrients, a commonly invoked hypothesis is that the improvement to plant defense when grown with AMF is simply due to an increased availability of nutrients. An alternative hypothesis is that the AMF effect on herbivory is due to changes in plant defense gene expression that are not simply due to nutrient availability. In this study, we tested whether changes in plant defenses are regulated by nutritional provisioning alone or the response of plant to AMF associations. Maize plants grown with or without AMF and with one of three fertilizer treatments (standard, 2 × nitrogen, or 2 × phosphorous) were infested with fall armyworm (Spodoptera frugiperda; FAW) for 72 h. We measured general plant characteristics (e.g. height, number of leaves), relative gene expression (rtPCR) of three defensive genes (lox3, mpi, and pr5), total plant N and P nutrient content, and change in FAW mass per plant. RESULTS: We found that AMF drove the defense response of maize by increasing the expression of mpi and pr5. Furthermore, while AMF increased the total phosphorous content of maize it had no impact on maize nitrogen. Fertilization alone did not alter upregulation of any of the 3 induced defense genes tested, suggesting the mechanism through which AMF upregulate defenses is not solely via increased N or P plant nutrition. CONCLUSION: This work supports that maize defense may be optimized by AMF associations alone, reducing the need for artificial inputs when managing FAW.

Transition in plant-plant facilitation in response to soil water and phosphorus availability in a legume-cereal intercropping system.

BACKGROUND: The tradeoff between negative and positive interactions of facilitated species and facilitators may depend on the degree of resource availability in agroecosystems. However, the rhizospheric mechanisms driving trade-offs that occur along phosphorus (P) and water availability gradients have not yet been systematically clarified. We established three types of root isolation conditions (no barrier, nylon barrier and solid barrier) at different P and water addition levels to address the above issue in a maize-grass pea intercropping system. RESULTS: The total yield and biomass net effect (NE) and the relative interaction index (RII) were significantly higher than 0 under all environmental conditions, demonstrating that plant-plant interactions generated positive effects in the intercropping system. The maize yield and biomass RII were 0.029-0.095 and 0.018-0.066, respectively, which indicated that maize growth was constantly facilitated. However, the RII for grass pea yield and biomass exhibited a different trend in comparison with maize. It was higher than 0 (as the facilitated species) under low soil P and moisture conditions and transitioned to values lower than 0 (facilitator species) under high P and moisture conditions, which showed that the type and intensity of plant-plant interactions steadily shifted with the applied stressors. Direct interactions decreased the maize rhizospheric soil pH by 1.5% and 1.9% under Low-P conditions. Notably, the rhizospheric soil acid and alkaline phosphatase secretions of maize and grass pea increased by 17.4-27.4% and 15.3-27.7%, respectively, in P-deficient soils. These results show that plant-plant interactions can effectively relieve P stress by mineralizing organophosphorus in P-deficient soils. Furthermore, the above tendency became more pronounced under drought-stressed conditions. The nylon barrier partially restricted the exchange and utilization of available nutrients and decreased the total yield and biomass by 1.8-7.8% and 1.1-7.8%, respectively. The presence of a solid barrier completely restricted interspecific rhizospheric interactions and decreased the total yield and biomass by 2.1-13.8% and 1.6-15.7%, respectively. Phytate and KH2PO4 addition intensified asymmetric interspecific competition, and grass pea was consistently subjected to competitive pressures. CONCLUSION: Briefly, the tradeoff between facilitation and competition was driven by rhizospheric interactions, and the transition in the intensity and type of interaction was highly dependent on resource availability in a biologically diverse system.

Joint GWAS and WGCNA uncover the genetic control of calcium accumulation under salt treatment in maize seedlings.

Soil salinization is an important factor threatening the yield and quality of maize. Ca2+ plays a considerable role in regulating plant growth under salt stress. Herein, we examined the shoot Ca2+ concentrations, root Ca2+ concentrations, and transport coefficients of seedlings in an association panel composed of 305 maize inbred lines under normal and salt conditions. A genome-wide association study was conducted by using the investigated phenotypes and 46,408 single-nucleotide polymorphisms of the panel. As a result, 53 significant SNPs were specifically detected under salt treatment, and 544 genes were identified in the linkage disequilibrium regions of these SNPs. According to the expression data of the 544 genes, we carried out a weighted coexpression network analysis. Combining the enrichment analyses and functional annotations, four hub genes (GRMZM2G051032, GRMZM2G004314, GRMZM2G421669, and GRMZM2G123314) were finally determined, which were then used to evaluate the genetic variation effects by gene-based association analysis. Only GRMZM2G123314, which encodes a pentatricopeptide repeat protein, was significantly associated with Ca2+ transport and the haplotype G-CT was identified as the superior haplotype. Our study brings novel insights into the genetic and molecular mechanisms of salt stress response and contributes to the development of salt-tolerant varieties in maize.

A multiple ion-uptake phenotyping platform reveals shared mechanisms affecting nutrient uptake by roots.

Nutrient uptake is critical for crop growth and is determined by root foraging in soil. Growth and branching of roots lead to effective root placement to acquire nutrients, but relatively little is known about absorption of nutrients at the root surface from the soil solution. This knowledge gap could be alleviated by understanding sources of genetic variation for short-term nutrient uptake on a root length basis. A modular platform called RhizoFlux was developed for high-throughput phenotyping of multiple ion-uptake rates in maize (Zea mays L.). Using this system, uptake rates were characterized for the crop macronutrients nitrate, ammonium, potassium, phosphate, and sulfate among the Nested Association Mapping (NAM) population founder lines. The data revealed substantial genetic variation for multiple ion-uptake rates in maize. Interestingly, specific nutrient uptake rates (nutrient uptake rate per length of root) were found to be both heritable and distinct from total uptake and plant size. The specific uptake rates of each nutrient were positively correlated with one another and with specific root respiration (root respiration rate per length of root), indicating that uptake is governed by shared mechanisms. We selected maize lines with high and low specific uptake rates and performed an RNA-seq analysis, which identified key regulatory components involved in nutrient uptake. The high-throughput multiple ion-uptake kinetics pipeline will help further our understanding of nutrient uptake, parameterize holistic plant models, and identify breeding targets for crops with more efficient nutrient acquisition.

Performance of Daphnia magna on flour, leaves, and pollen from different maize lines: Implications for risk assessment of genetically engineered crops.

Non-target effects of genetically engineered (GE) plants on aquatic Daphnia magna have been studied by feeding the species with different maize materials containing insecticidal Cry proteins from Bacillus thuringiensis (Bt). The results of those studies were often difficult to interpret, because only one GE plant was compared to one related non-GE control. In such a setting, effects of the Cry proteins cannot be distinguished from plant background effects, in particular when the test species is nutritionally stressed. In the present study, we tested the suitability of three different maize materials, i.e., flour, leaves and pollen, from five diverse non-GE maize lines (including EXP 258, a breeding line that is closely related to a SmartStax Bt maize) as exclusive food sources for D. magna. The parameters recorded included survival, sublethal endpoints such as body size, number of moltings to first offspring, time to first offspring, number of individuals in first clutch, total number of clutches, total number of offspring, average number of offspring per clutch, and population measures such as net reproductive rate R0, generation time T and intrinsic rate of increase rm. The results showed that D. magna can survive, grow and reproduce when fed only maize materials, although the performance was poorer than when fed algae, which indicates nutritional stress. Large differences in life table and population parameters of D. magna were observed among the different maize lines. Our results suggest that confounding effects caused by nutritional stress and plant background might explain some of the conflicting results previously published on the effects of Bt crops on D. magna. Using 95% confidence intervals for the means of the five maize lines for all measured parameters of D. magna performance in our study, we captured the natural range of variation. This information is useful for the interpretation of observed differences in D. magna performance between a GE plant and its non-GE comparator as it helps judging whether observed effects are of biological relevance. If differences between a GE and comparator line are observed and their biological relevance needs to be assessed in future risk assessments of GE maize, 1) the data on natural variation of the different parameters generated by previous studies can be informative (e.g. data from our study for maize fed D. magna); 2) for additional experiments the inclusion of multiple unrelated non-GE comparators should be considered; In addition, it should be taken into account that nutritional stress can affect the outcome of the study.

A transposon surveillance mechanism that safeguards plant male fertility during stress.

Although plants are able to withstand a range of environmental conditions, spikes in ambient temperature can impact plant fertility causing reductions in seed yield and notable economic losses1,2. Therefore, understanding the precise molecular mechanisms that underpin plant fertility under environmental constraints is critical to safeguarding future food production3. Here, we identified two Argonaute-like proteins whose activities are required to sustain male fertility in maize plants under high temperatures. We found that MALE-ASSOCIATED ARGONAUTE-1 and -2 associate with temperature-induced phased secondary small RNAs in pre-meiotic anthers and are essential to controlling the activity of retrotransposons in male meiocyte initials. Biochemical and structural analyses revealed how male-associated Argonaute activity and its interaction with retrotransposon RNA targets is modulated through the dynamic phosphorylation of a set of highly conserved, surface-located serine residues. Our results demonstrate that an Argonaute-dependent, RNA-guided surveillance mechanism is critical in plants to sustain male fertility under environmentally constrained conditions, by controlling the mutagenic activity of transposons in male germ cells.

When the average hides the risk of Bt-corn pollen on non-target Lepidoptera: Application to Aglais io in Catalonia.

Field cultivation of Genetically Modified (GM) Bt-plants has a potential environmental risk toward non-target Lepidoptera (NTLs) larvae through the consumption of Bt-maize pollen. The Bt-maize Cry protein targeting Lepidoptera species detrimental to the crop is also expressed in pollen which is dispersed by wind and can thus reach habitats of NTLs. To better assess the current ecological risk of Bt-maize at landscape scales, we developed a spatially-explicit exposure-hazard model considering (i) the dynamics of pollen dispersal obtained by convolving GM plants emission with a dispersal kernel and (ii) a toxicokinetic-toxicodynamic (TKTD) model accounting for the impact of toxin ingestion on individual lethal effects. We simulated the model using real landscape observations in Catalonia (Spain): GM-maize locations, flowering dates, rainfall time series and larvae emergence date of the European peacock butterfly Aglais io. While in average, the additional mortality appears to be negligible, we show significant additional mortality at sub-population level, with for instance a mortality higher than 40% within the 10m for the 10% most Bt-sensitive individuals. Also, using Pareto optimality we capture the best trade-off between isolation distance and additional mortality: up to 50 m are required to significantly buffer Bt-pollen impact on NTLs survival at the individual level. Our study clears up the narrow line between diverging conclusions: those claiming no risk by only looking at the average regional effect of Bt on NTLs survival and those pointing out a significant threaten when considering the variability of individuals mortality.

Phosphorus fertilization and mycorrhizal colonization change silver nanoparticle impacts on maize.

Environmental risks of silver (Ag) nanoparticles (NPs) have aroused considerable concern, however, their ecotoxicity in soil-plant systems has yet not been well elaborated, particularly in agroecosystems with various fertility levels and soil biota. The aims of the present study were to determine AgNPs impacts on maize as influenced by mycorrhizal inoculation and P fertilization. A greenhouse pot experiment was conducted determine the effects of mycorrhizal inoculation with Rhizophagus intraradices and P fertilization (0, 20, and 50 P mg/kg soil, as Ca(H2PO4)2) on plant growth, Ag accumulation and physiological responses of maize exposed to AgNPs (1 mg/kg), or an equivalent Ag+. Overall, AgNPs and Ag+ did not significantly affect plant biomass and acquisition of mineral nutrients, activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), chlorophyll contents and photosystem (PS) II photochemical efficiency. In most cases, AgNPs and Ag+ caused similar Ag accumulation in plant tissues. P fertilization significantly increased Ag bioavailability and plant Ag accumulation, but only promoted the growth and P uptake of nonmycorrhizal plants. AM inoculation produced positive impacts on plant biomass, nutritional and physiological responses, but slightly affected extractable Ag in soil and Ag accumulation in plants. Mycorrhizal responses in plant growth and P uptake were more pronounced in the treatments without P but with Ag. By and large, AgNPs exhibited similar phytoavailability, phytoaccumulation and low phytotoxicity compared to Ag+, but higher fungitoxicity (i.e., lower root colonization). In conclusion, both AM inoculation and P fertilization can improve plant performance in the soil exposed to Ag, but P increases environmental risk of Ag. Our results indicate a beneficial role of arbuscular mycorrhizal fungi but a dual role of P in soil-plant systems exposed to AgNPs or Ag+.

Proteomic analysis reveals the role of exogenous cysteine in alleviating chromium stress in maize seedlings.

Cysteine (Cys) is incorporated into several compounds which are involved in detoxification of heavy metals. It is evident from recent studies that Cys is effective in alleviating the toxicity of heavy metals. Nevertheless, little is known about the Cys-mediated alleviation of chromium (Cr) toxicity. In our study, the impacts of exogenous Cys on Cr-stressed maize (Zea mays L.) were examined by using physiological and proteomic analyses. The results showed that Cr (100 µM) increased the accumulation of hydrogen peroxide, decreased cell viability, enhanced lipid peroxidation and consequently inhibited plant growth. The application of Cys (500 µM) attenuated the adverse effects of Cr on seedling growth. Cys supplementation to Cr treated plants decreased Cr accumulation in the shoots and increased Cr accumulation in roots. Cys treatment also modulated the activities of antioxidant enzymes and increased endogenous Cys content. Sixty proteins in root tissue were significantly affected by exogenous Cys under Cr stress using two-dimensional electrophoresis. Forty-six differentially expressed proteins were successfully identified by MALDI-TOF/TOF mass spectrometry. These differentially expressed proteins were involved in various biological pathways such as stress response (41.3%), energy and carbohydrate metabolism (21.7%), protein metabolism (6.5%), amino acid metabolism (6.5%), and others of unknown functions. The defense response-related proteins including glutathione peroxidase, glutathione S-transferases, pathogenesis-related proteins, glyoxalases and superoxide dismutase were differently regulated by Cys suggesting their roles in the Cys-mediated Cr tolerance.

The unusual dRemp retrotransposon is abundant, highly mutagenic, and mobilized only in the second pollen mitosis of some maize lines.

The frequent mutations recovered recently from the pollen of select maize lines resulted from the meiotic mobilization of specific low-copy number long-terminal repeat (LTR) retrotransposons, which differ among lines. Mutations that arise at male meiosis produce kernels with concordant mutant phenotypes in both endosperm and embryo because the two sperms that participate in double fertilization are genetically identical. Those are in a majority. However, a small minority of kernels with a mutant endosperm carry a nonconcordant normal embryo, pointing to a postmeiotic or microgametophytic origin. In this study, we have identified the basis for those nonconcordant mutations. We find that all are produced by transposition of a defective LTR retrotransposon that we have termed dRemp (defective retroelement mobile in pollen). This element has several unique properties. Unlike the mutagenic LTR retrotransposons identified previously, dRemp is present in hundreds of copies in all sequenced lines. It seems to transpose only at the second pollen mitosis because all dRemp insertion mutants are nonconcordant yet recoverable in either the endosperm or the embryo. Although it does not move in most lines, dRemp is highly mobile in the Corn Belt inbred M14, identified earlier by breeders as being highly unstable. Lastly, it can be recovered in an array of structures, ranging from solo LTRs to tandem dRemp repeats containing several internal LTRs, suggestive of extensive recombination during retrotransposition. These results shed further light on the spontaneous mutation process and on the possible basis for inbred instability in maize.

Liming effects of poultry litter derived biochar on soil acidity amelioration and maize growth.

Crop production in acid soils is facing enormous challenges due to low soil quality associated with an increase in the acidification rate and aluminum toxicity. Despite comprehensive prior work with biochar application on nutrient availability and crop productivity in acid soils, little information is available about the recommendation or standardization of biochar application rates that are more suitable for soil fertility improvement under different soil environments (physico-chemical properties) for maximizing the benefits of biochar applications and minimizing the potential environmental risk. Thus, the objective of this study was to investigate the effectiveness of poultry litter (PL) and poultry litter biochar (PLB) in ameliorating the fertility of acid soils through incubation and pot experiments. The soil was amended with different materials as follows; lime (1 g kg-1), PL (5, 10 and 15 g kg-1) and PLB (5, 10 and 15 g kg-1) along with control (non-amended). A pot experiment was also conducted using similar treatments to observe the responses of maize crop to the different amendments. The results indicated an increase in the pH and a decrease in exchangeable acidity in lime, PL and PLB amended soils. Lower soil pH, base cations and soil available phosphorus (P), and higher exchangeable acidity were found in control than the amended soils. Compared to PL and lime, PLB achieved greater increase rate in soil pH and reduction rate in soil exchangeable acidity with increased soil exchangeable base cations. An increase in soil available calcium (Ca) was observed in the lime treatment, while in PL and PLB treatments, there was an increase in soil available Ca, magnesium (Mg), potassium (K) and P. Application of the amendments increased availability of nitrogen (N), P, K, Ca and Mg relative to the control for maize in the pot experiment. When PL and PLB amendments were compared, it was found that the PLB was the best choice for the amelioration of acid soils as well as nutrient uptake by maize plants. It is suggested that application of PLB at the rate of 15 g kg-1 is suitable for maize growth in acid soils.

Phosphorus addition increased carbon partitioning to autotrophic respiration but not to biomass production in an experiment with Zea mays.

Plant carbon (C) partitioning-the relative use of photosynthates for biomass production, respiration, and other plant functions-is a key but poorly understood ecosystem process. In an experiment with Zea mays, with or without arbuscular mycorrhizal fungi (AMF), we investigated the effect of phosphorus (P) fertilization and AMF on plant C partitioning. Based on earlier studies, we expected C partitioning to biomass production (i.e., biomass production efficiency; BPE) to increase with increasing P addition due to reduced C partitioning to AMF. However, although plant growth was clearly stimulated by P addition, BPE did not increase. Instead, C partitioning to autotrophic respiration increased. These results contrasted with our expectations and with a previous experiment in the same set-up where P addition increased BPE while no effect on autotropic respiration was found. The comparison of both experiments suggests a key role for AMF in explaining these contrasts. Whereas in the previous experiment substantial C partitioning to AMF reduced BPE under low P, in the current experiment, C partitioning to AMF was too low to directly influence BPE. Our results illustrate the complex influence of nutrient availability and mycorrhizal symbiosis on plant C partitioning.

Sulfur-enriched leonardite and humic acid soil amendments enhance tolerance to drought and phosphorus deficiency stress in maize (Zea mays L.).

Soil amendments are known to promote several plant growth parameters. In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. Considering the climate change scenario, drought and related stress factors will be even more severe endangering the global food security. Therefore, two parallel field trials were conducted to examine at what extent soil amendment of leonardite and humic acid would affect drought and phosphorus tolerance of maize. The treatments were: control (C: 100% A pan and 125 kg P ha-1), P deficiency (phosphorus stress (PS): 62.5 kg P ha-1), water deficit stress (water stress (WS): 67% A pan), and PS + WS (67% A pan and 62.5 kg P ha-1). Three organic amendments were (i) no amendment, (ii) 625 kg S + 750 kg leonardite ha-1 and (iii) 1250 kg S + 37.5 kg humic acid ha-1) tested on stress treatments. Drought and P deficiency reduced plant biomass, grain yield, chlorophyll content, Fv/Fm, RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H2O2 in maize plants. The combined stress of drought and P deficiency decreased further related plant traits. Humic acid and leonardite enhanced leaf P and yield in maize plants under PS. A significant increase in related parameters was observed with humic acid and leonardite under WS. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. The use of sulfur-enriched amendments can be used effectively to maintain yield of maize crop in water limited calcareous soils.

Radio frequency treatment accelerates drying rates and improves vigor of corn seeds.

This research explored the application of combined radio frequency and hot air drying (RF-HAD) technology on corn seeds. Drying characteristics and seed vigor were investigated at different RF electrode gaps (140, 150 and 160 mm). To better demonstrate the feasibility of applying RF-HAD on corn seeds, tempering-intermittent hot air drying (HAD) was studied as a comparison. Reduced electrode gap corresponding to elevated average heating rate and power efficiency resulted in decreased seeds vigor and specific energy consumption. The assistance of RF significantly increased the drying rate of corn seeds and reduced drying duration by up to 70% compared with HAD. A higher dehydrogenase activity (DHA) but a lower germination percentage (GP) was observed in RF-HAD samples as compared with HAD ones. Corn seeds were promoted to be dormant by RF-HAD according to dormancy-breaking results and isobaric tags for relative and absolute quantification (iTRAQ) analysis.

Oxylipins Other Than Jasmonic Acid Are Xylem-Resident Signals Regulating Systemic Resistance Induced by Trichoderma virens in Maize.

Multiple long-distance signals have been identified for pathogen-induced systemic acquired resistance, but mobile signals for symbiont-induced systemic resistance (ISR) are less well understood. We used ISR-positive and -negative mutants of maize (Zea mays) and the beneficial fungus Trichoderma virens and identified 12-oxo-phytodienoic acid (12-OPDA) and α-ketol of octadecadienoic acid (KODA) as important ISR signals. We show that a maize 13-lipoxygenase mutant, lox10, colonized by the wild-type T. virens (TvWT) lacked ISR response against Colletotrichum graminicola but instead displayed induced systemic susceptibility. Oxylipin profiling of xylem sap from T. virens-treated plants revealed that 12-OPDA and KODA levels correlated with ISR. Transfusing sap supplemented with 12-OPDA or KODA increased receiver plant resistance in a dose-dependent manner, with 12-OPDA restoring ISR of lox10 plants treated with TvWT or T. virens Δsm1, a mutant unable to induce ISR. Unexpectedly, jasmonic acid (JA) was not involved, as the JA-deficient opr7 opr8 mutant plants retained the capacity for T. virens-induced ISR. Transcriptome analysis of TvWT-treated maize B73 revealed upregulation of 12-OPDA biosynthesis and OPDA-responsive genes but downregulation of JA biosynthesis and JA response genes. We propose a model that differential regulation of 12-OPDA and JA in response to T. virens colonization results in ISR induction.

Male Sterility in Maize after Transient Heat Stress during the Tetrad Stage of Pollen Development.

Shifts in the duration and intensity of ambient temperature impair plant development and reproduction, particularly male gametogenesis. Stress exposure causes meiotic defects or premature spore abortion in male reproductive organs, leading to male sterility. However, little is known about the mechanisms underlying stress and male sterility. To elucidate these mechanisms, we imposed a moderate transient heat stress on maize (Zea mays) plants at the tetrad stage of pollen development. After completion of pollen development at optimal conditions, stress responses were assessed in mature pollen. Transient heat stress resulted in reduced starch content, decreased enzymatic activity, and reduced pollen germination, resulting in sterility. A transcriptomic comparison pointed toward misregulation of starch, lipid, and energy biosynthesis-related genes. Metabolomic studies showed an increase of Suc and its monosaccharide components, as well as a reduction in pyruvate. Lipidomic analysis showed increased levels of unsaturated fatty acids and decreased levels of saturated fatty acids. In contrast, the majority of genes involved in developmental processes such as those required for auxin and unfolded protein responses, signaling, and cell wall biosynthesis remained unaltered. It is noteworthy that changes in the regulation of transcriptional and metabolic pathway genes, as well as heat stress proteins, remained altered even though pollen could recover during further development at optimal conditions. In conclusion, our findings demonstrate that a short moderate heat stress during the highly susceptible tetrad stage strongly affects basic metabolic pathways and thus generates germination-defective pollen, ultimately leading to severe yield losses in maize.

Haploid male fertility and spontaneous chromosome doubling evaluated in a diallel and recurrent selection experiment in maize.

KEY MESSAGE: Mainly additive gene action governed inheritance of haploid male fertility, although epistatic effects were also significant. Recurrent selection for haploid male fertility resulted in substantial improvement in this trait. The doubled haploid (DH) technology offers several advantages in maize breeding compared to the traditional method of recurrent selfing. However, there is still great potential for improving the success rate of DH production. Currently, the majority of haploid plants are infertile after chromosome doubling treatment by antimitotic agents such as colchicine and cannot be selfed for production of DH lines. Improvement in haploid male fertility (HMF) by selection for a higher spontaneous chromosome doubling rate (SDR) has the potential to increase DH production efficiency. To investigate the gene action governing SDR in two breeding populations, we adapted the quantitative-genetic model of Eberhart and Gardner (in Biometrics 22:864-881. https://doi.org/10.2307/2528079 , 1966) for the case of haploid progeny from ten DH lines and corresponding diallel crosses. Furthermore, we carried out three cycles of recurrent selection for SDR in two additional populations to evaluate the selection gain for this trait. Additive genetic effects predominated in both diallel crosses, but epistatic effects were also significant. Entry-mean heritability of SDR observed for haploid progeny of these populations exceeded 0.91, but the single-plant heritability relevant to selection was low, ranging from 0.11 to 0.19. Recurrent selection increased SDR from approximately 5-50%, which suggests the presence of few QTL with large effects. This improvement in HMF is greater than the effect of standard colchicine treatment, which yields at maximum 30% fertile haploids. Altogether, the results show the great potential of spontaneous chromosome doubling to streamline development DH lines and to enable new breeding schemes with more efficient allocation of resources.