A field experiment with elevated atmospheric CO2-mediated changes to C4 crop-herbivore interactions

Myco-Synergism Boosts Herbivory-Induced Maize Defense by Triggering Antioxidants and Phytohormone Signaling

BACKGROUND

Biocontrol strategies are the best possible and eco-friendly solution to develop resistance against O furnacalis and improve the maize yield. However, the knowledge about underlying molecular mechanisms, metabolic shifts, and hormonal signaling is limited.

METHODS

Here, we used an axenic and a consortium of entomopathogenic Beauveria bassiana OFDH1-5 and a pathogen-antagonistic Trichoderma asperellum GDFS1009 in maize and observed that consortium applications resulted in higher chlorophyll contents and antioxidants activities [superoxide dismutase (SOD), peroxidase (POD), proline, protease, and polyphenol oxidase (PPO)] with a decrease in O. furnacalis survival. We performed a comprehensive transcriptome and an untargeted metabolome profiling for the first time at a vegetative stage in fungal inoculated maize leaves at 0-, 12-, 24-, 48-, and 72-h post insect infestation.

RESULTS

The consortium of B. bassiana and T. asperellum leads to 80-95% of O. furnacalis mortality. A total of 13,156 differentially expressed genes were used for weighted gene coexpression network analysis. We identified the six significant modules containing thirteen candidate genes [protein kinase (GRMZM2G025459), acyl-CoA dehydrogenase (GRMZM5G864319), thioredoxin gene (GRMZM2G091481), glutathione S-transferase (GRMZM2G116273), patatin-like phospholipase gene (GRMZM2G154523), cytochrome P450 (GRMZM2G139874), protease inhibitor (GRMZM2G004466), (AC233926.1_FG002), chitinase (GRMZM2G453805), defensin (GRMZM2G392863), peroxidase (GRMZM2G144153), GDSL- like lipase (AC212068.4_FG005), and Beta-glucosidase (GRMZM2G031660)], which are not previously reported that are highly correlated with Jasmonic acid - Ethylene (JA-ET) signaling pathway and antioxidants. We detected a total of 130 negative and 491 positive metabolomic features using a ultrahigh-performance liquid chromatography ion trap time-of-flight mass spectrometry (UHPLC-QTOF-MS). Intramodular significance and real time-quantitative polymerase chain reaction (RT-qPCR) expressions showed that these genes are the true candidate genes. Consortium treated maize had higher jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) levels.

CONCLUSION

Our results provide insights into the genetics, biochemicals, and metabolic diversity and are useful for future biocontrol strategies against ACB attacks.

Long-Term Effect of Elevated CO2 on the Development and Nutrition Contents of the Pea Aphid (Acyrthosiphon pisum)

It is predicted that the current atmospheric CO2 level will be doubled by the end of this century. Here, we investigate the impacts of elevated CO2 (550 and 750 μL/L) on the development and nutrition status of the green pea aphid for six generations, which is longer than previous studies. All seven examined physiological parameters were not affected over six generations under the ambient CO2 level (380 μL/L). However, the elevated CO2 levels (550 and 750 μL/L) prolonged nymph duration, decreased adult longevity, female fecundity and protein content, and increased the contents of total lipid, soluble sugar and glycogen. There was a significant interaction between the effect of CO2 levels and the effect of generations on nymph duration, female fecundity and adult longevity. The elevated CO2 had immediate effects on the female fecundity and the contents of total protein, total lipid and soluble sugar, starting within F0 generation. The adult longevity decreased, and the glycogen content increased from the F1 generation. However, the significant effect on the nymph development was only observed after three generations. Our study indicates that the elevated CO2 levels first influence the reproduction, the nutrition and the energy supply, then initiate aphid emergency responses by shortening lifespan and increasing glucose metabolism, and finally result in the slow development under further persistent elevated CO2 conditions after three generations, possibly leading to population decline under elevated CO2 conditions. Our results will guide further field experiments under climate change conditions to evaluate the effects of elevated CO2 on the development of the pea aphids and other insects, and to predict the population dynamics of the green pea aphid.

Effects of elevated CO2 on resistant and susceptible rice cultivar and its primary host, brown planthopper (BPH), Nilaparvata lugens (Stål)

The elevated CO2 (eCO2) has positive response on plant growth and negative response on insect pests. As a contemplation, the feeding pattern of the brown plant hopper, Nilaparvata lugens Stål on susceptible and resistant rice cultivars and their growth rates exposed to eCO2 conditions were analyzed. The eCO2 treatment showed significant differences in percentage of emergence and rice biomass that were consistent across the rice cultivars, when compared to the ambient conditions. Similarly, increase in carbon and decrese in nitrogen ratio of leaves and alterations in defensive peroxidase enzyme levels were observed, but was non-linear among the cultivars tested. Lower survivorship and nutritional indices of N. lugens were observed in conditions of eCO2 levels over ambient conditions. Results were nonlinear in manner. We conclude that the plant carbon accumulation increased due to eCO2, causing physiological changes that decreased nitrogen content. Similarly, eCO2 increased insect feeding, and did alter other variables such as their biology or reproduction.

Voltine Ecotypes of the Asian Corn Borer and Their Response to Climate Warming

Simple Summary

The Asian corn borer (ACB), Ostrinia furnacalis, is an important economic pest of corn and other crops, and is widely distributed in China. Depending on the climate, ACB may have one or up to seven generations each year, from north to south, respectively. The degree of crop damage is closely related to its phenology and number of generations per year (voltinism). Climate warming may result in an alternation of voltinism in the ACB. In the present study, we investigated the voltinism of different populations under different simulated environments. From the diapause response, both the uni- and multivoltine ecotypes were coexisting in the Harbin (H) population collected from action sites of ACB moths in Harbin, Heilongjiang Province, China. Diapause incidence declined given the climate-warming scenario, which was temporally specific and could be overridden by significantly low daily average temperatures. Elevated CO₂ did not directly impact voltinism. On the basis of voltinism, the H population reflected sympatric uni- and multivoltine ecotypes, with multivoltinism being dominant. The univoltinism trait was recessive. Climate warming could significantly override photoperiod effects. Warmer temperatures and declining latitude (reduced daylength), and their interaction, are estimated to drive ACB evolution to increased homogeneity and multivoltinism.

Abstract

In the Asian corn borer (ACB), Ostrinia furnacalis (Guenée), diapause is governed by a multigenetic constitution that responds to daylength and temperature with seasonality. The ACB displays uni- or multivoltinism, depending on its geographic specificity. Hence, warmer temperatures may result in alternation of voltinism in the ACB, which will help in understanding the ecological consequences of climate warming on insects. In the present study, we investigated the voltinism in two natural populations from Harbin (H) and Gongzhuling (G) as well as a laboratory (L) population (established from the H population in 2017) of the ACB, at ambient and elevated atmospheric CO₂ (aCO₂ 390 μL/L and eCO₂ 750 μL/L) and temperature (aT and Et = At + 2 °C). From the diapause response, both the uni- and multivoltine ecotypes were coexisting in the H population. The neonate occurrence date of 50% individuals that induced diapause was ca. 10 days later in the G population than in the H population, but it was about 10 days earlier than in the L population. Comparing to the dates of onset and the peak of diapause induction, the G and L populations were less variable than the H population in response to a short and/or shortening daylength in the field. The univoltine individuals could not be eliminated completely after 19 generations of selection. Diapause incidence decreased with a climate-warming scenario, which was temporally specific and could be overridden by significantly low daily average temperatures. The eCO₂ did not directly impact the voltinism. On the basis of voltinism, the H population was sympatric for uni- and multivoltine ecotypes, with multivoltinism being dominant. The univoltinism trait was recessive. Climate warming could significantly override the effect of photoperiod, which was yearly dependent. Warmer temperatures and a decreased latitude (shortened daylength), and their interaction, would drive ACB evolution toward diapause homogeneity for multivoltinism.

Synergistic Effect of Beauveria bassiana and Trichoderma asperellum to Induce Maize (Zea mays L.) Defense against the Asian Corn Borer, Ostrinia furnacalis (Lepidoptera, Crambidae) and Larval Immune Response

Ostrinia furnacalis, is the major pest of maize causing significant yield losses. So far, many approaches have been used to increase the virulence of entomopathogenic fungal isolates. The current study is an attempt to estimate synergistic effect of Beauveria bassiana and Trichoderma asperellum in order to explore larval immune response through RNA sequencing and differentially expression analysis. In vivo synergism was examined in seven proportions (B. bassiana: T. asperellum = 1:1, 1:2, 1:3, 1:4, 4:1, 3:1, 2:1) and in the in vitro case, two inoculation methods were applied: seed coating and soil drenching. Results revealed significant decrease in plant damage and high larval mortality in fungal treatments. Fungal isolates mediated the plant defense by increasing proline, superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO) and protease activities. Seed coating method was proved to be the most effective in case of maize endophytic colonization. In total, 59 immune-related differentially expressed genes DEGs were identified including, cytochrome P450, heat shock protein, ABC transporter, cadherin, peptidoglycan recognition protein (PGRP), cuticlular protein, etc. Further, transcriptomic response was confirmed by qRT-PCR. Our results concluded that, coculture of B. bassiana and T. asperellum has the synergistic potential to suppress the immune response of O. furnacalis and can be used as sustainable approach to induce plant resistance through activation of defense-related enzymes.

Photosynthesis and yield response to elevated CO2, C4 plant foxtail millet behaves similarly to C3 species

Foxtail millet (Setaria italica) is a nutrient-rich food source traditionally grown in arid and semi-arid areas, as it is well adapted to drought climate. Yet there is limited information as how the crop responses to the changing climate. In order to investigate the response of foxtail millet to elevated [CO₂] and the underlying mechanism, the crop was grown at ambient [CO₂] (400 μmol mol^-1) and elevated [CO₂] (600 μmol mol^-1) in an open-top chamber (OTC) experimental facility in North China. The changes in leaf photosynthesis, chlorophyll fluorescence, biomass, yield and global gene expression in response to elevated [CO₂] were determined. Despite foxtail millet being a C₄ photosynthetic crop, photosynthetic rates (P_N) and intrinsic water-use efficiency (WUEi), were increased under elevated [CO₂]. Similarly, grain yield and above-ground biomass also significantly increased (P <  0.05) for the two years of experimentation under elevated [CO₂]. Increases in seeds and tiller number, spike and stem weight were the main contributors to the increased grain yield and biomass. Using transcriptomic analyses, this study further identified some genes which play a role in cell wall reinforcement, shoot initiation, stomatal conductance, carbon fixation, glycolysis / gluconeogenesis responsive to elevated [CO₂]. Changes in these genes reduced plant height, increased stem diameters, and promote CO₂ fixation. Higher photosynthetic rates at elevated [CO₂] demonstrated that foxtail millet was not photosynthetically saturated at elevated [CO₂] and its photosynthesis response to elevated [CO₂] were analogous to C₃ plants.

Elevated atmospheric CO2 concentrations alter grapevine (Vitis vinifera) systemic transcriptional response to European grapevine moth (Lobesia botrana) herbivory

Atmospheric carbon dioxide (CO₂) concentrations are among the chief factors shaping the mode and magnitude of interactions between plants and herbivorous insects. Here, we describe the first global analysis of systemic transcriptomic responses of grapevine Vitis vinifera plants to feeding of European grapevine moth Lobesia botrana larvae at future elevated CO₂ concentrations. The study was conducted on mature, fruit-bearing grapevine plants under ambient and elevated CO₂ concentrations in a grapevine free-air carbon dioxide enrichment (FACE) facility. Grapevine transcriptional response to herbivory was clearly dependent on phenological stage, with a higher number of differentially expressed genes identified at fruit development compared to berry ripening. At fruit development, more transcripts were differentially expressed as a response to herbivory under elevated compared to ambient CO₂ concentrations. Classification of the respective transcripts revealed that in particular genes involved in metabolic pathways, biosynthesis of secondary metabolites and plant-pathogen interactions were significantly enriched. Most of these genes had similar expression patterns under both CO₂ concentrations, with a higher fold-change under elevated CO₂ concentrations. Differences in expression levels of a subset of herbivory responsive genes were further validated by RT-qPCR. Our study indicates that future elevated CO₂ concentrations will affect interactions between grapevine plants and one of its key insect pests, with consequences for future relevance of L. botrana in worldwide viticulture.

CO2 fixation in above-ground biomass of summer maize under different tillage and straw management treatments

This study was conducted to quantify the potential for CO₂ fixation in the above-ground biomass of summer maize (Zea mays L.) under different tillage and residue retention treatments. The treatments were paired and included conventional tillage with straw removed (CT₀), conventional tillage with straw retained (CT_S), no-till with straw removed (NT₀), no-till with straw retention (NT_S), subsoiling with straw removed (SS₀), and subsoiling with straw retained (SS_S). The results indicated that NT_S and SS_S can enhance translocation of photosynthates to grains during the post-anthesis stage. SS_S showed the highest total production (average of 7.8 Mg ha⁻¹), carbon absorption by crop (Cd) (average of 9.2 Mg C ha⁻¹), and total C absorption (Ct) (average of 40.4 Mg C ha⁻¹); and NT_S showed the highest contribution of post-anthesis dry matter translocation to grain yield (average of 74%). Higher CO₂ emission intensity and CO₂ fixation efficiency (CFE) were observed for straw retention treatments. In comparison with CT_S, the mean CFE (%) over four years increased by 26.3, 19.0, 16.5, and 9.4 for NT₀, SS₀, NT_S, and SS_S, respectively. Thus, SS_S and NT_S systems offer the best options for removing CO₂ from the atmosphere while enhancing crop productivity of summer maize in the North China Plain.

Elevated carbon dioxide reduces emission of herbivore-induced volatiles in Zea mays

Terpene volatiles produced by sweet corn (Zea mays) upon infestation with pests such as beet armyworm (Spodoptera exigua) function as part of an indirect defence mechanism by attracting parasitoid wasps; yet little is known about the impact of climate change on this form of plant defence. To investigate how a central component of climate change affects indirect defence, we measured herbivore-induced volatile emissions in plants grown under elevated carbon dioxide (CO₂ ). We found that S. exigua infested or elicitor-treated Z. mays grown at elevated CO₂ had decreased emission of its major sesquiterpene, (E)-β-caryophyllene and two homoterpenes, (3E)-4,8-dimethyl-1,3,7-nonatriene and (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast, inside the leaves, elicitor-induced (E)-β-caryophyllene hyper-accumulated at elevated CO₂ , while levels of homoterpenes were unaffected. Furthermore, gene expression analysis revealed that the induction of terpene synthase genes following treatment was lower in plants grown at elevated CO₂ . Our data indicate that elevated CO₂ leads both to a repression of volatile synthesis at the transcriptional level and to limitation of volatile release through effects of CO₂ on stomatal conductance. These findings suggest that elevated CO₂ may alter the ability of Z. mays to utilize volatile terpenes to mediate indirect defenses.