The Protease Inhibitor CI2c Gene Induced by Bird Cherry-Oat Aphid in Barley Inhibits Green Peach Aphid Fecundity in Transgenic Arabidopsis

Comparative Transcriptome Analysis Reveals the Molecular Basis of Brassica napus in Response to Aphid Stress

Rapeseed is a globally important economic crop that can be severely impacted by aphids. However, our understanding of rapeseed resistance to aphid stress is very limited. In this study, we analyzed the resistance characteristics of the low aphid-susceptible variety APL01 and the highly aphid-susceptible variety Holly in response to aphid stress. APL01 had a more significant inhibitory effect on aphid proliferation compared with Holly during the early stage of inoculation, whereas Holly showed stronger tolerance to aphid stress compared with APL01 during the later stage of inoculation. Through transcriptome, physiological, and gene expression analyses, it was revealed that chitinase activity, catalase activity, calcium signal transduction, and activation of systemic acquired resistance might be involved in aphid resistance in B. napus. The degree of inhibition of photosynthesis in plants under aphid stress directly determines the tolerance of B. napus to aphid stress. Furthermore, four promising candidate genes were screened from eight genes related to rapeseed response to biotic stress through RT-qPCR analysis of gene expression levels. These research findings represent an important step forward in understanding the resistance of rapeseed to aphid stress and provide a solid foundation for the cloning of genes responsible for this resistance.

Differential defense responses of tropical grasses to Mahanarva spectabilis (Hemiptera: Cercopidae) infestation

The spittlebugs Mahanarva spectabilis economically challenges cattle production of neotropical regions, due to its voracious feeding on tropical grasses. Here, we evaluated biochemical responses of the interaction between M. spectabilis and the widely cultivated tropical grasses Brachiaria spp. (i.e., brizantha and decumbens) and elephant grasses (cvs. Roxo de Botucatu and Pioneiro), regarding lipoxygenases, protease inhibitors, phytohormones, and proteolytic activities in the midgut of M. spectabilis. The M. spectabilis-infested grasses increased lipoxygenases activity, except for cv. Pioneiro. The levels of the phytohormones jasmonic and abscisic acids were similarly low in all genotypes and increased under herbivory. Furthermore, salicylic acid concentration was constitutively higher in Brachiaria sp., increasing only in spittlebug-infested B. decumbens. M. spectabilis infestations did not induce increases of protease inhibitors in any forage grass type. The trypsin activity remained unaltered, and the total proteolytic activity increased only in B. decumbens-fed insects. Our findings revealed that most forage grasses exposed to spittlebugs activate the lipoxygenases pathway, resulting in increased abscisic and jasmonic acids. However, greater amounts of these hormones do not induce protease inhibitory activity in response to spittlebug attack. This knowledge certainly helps to guide future projects aiming at reducing the impact of spittlebugs on forage production.

Transcriptome profiling revealed potentially important roles of defensive gene expression in the divergence of insect biotypes: a case study with the cereal aphid Sitobion avenae

Background

Many insects can develop differential biotypes on variable host plants, but the underlying molecular factors and mechanisms are not well understood. To address this issue, transcriptome profiling analyses were conducted for two biotypes of the cereal aphid, Sitobion avenae (Fabricius), on both original and alternative plants.

Results

Comparisons between both biotypes generated 4174 differentially expressed unigenes (DEGs). In their response to host plant shift, 39 DEGs were shared by both biotypes, whereas 126 and 861 DEGs occurred only in biotypes 1 and 3, respectively. MMC (modulated modularity clustering) analyses showed that specific DEGs of biotypes 1 and 3 clustered into five and nine transcriptional modules, respectively. Among these DEGs, defense-related genes underwent intensive expression restructuring in both biotypes. However, biotype 3 was found to have relatively lower gene transcriptional plasticity than biotype 1. Gene enrichment analyses of the abovementioned modules showed functional divergence in defensive DEGs for the two biotypes in response to host transfer. The expression plasticity for some defense related genes was showed to be directly related to fecundity of S. avenae biotypes on both original and alternative plants, suggesting that expression plasticity of key defensive genes could have significant impacts on the adaptive potential and differentiation of S. avenae biotypes on different plants.

Conclusions

The divergence patterns of transcriptional plasticity in defense related genes may play important roles in the phenotypic evolution and differentiation of S. avenae biotypes. Our results can provide insights into the role of gene expression plasticity in the divergence of insect biotypes and adaptive evolution of insect populations.

Transcriptome Profiling Revealed Potentially Critical Roles for Digestion and Defense-Related Genes in Insects' Use of Resistant Host Plants: A Case Study with Sitobion Avenae

Using host plant resistance (HPR) in management of insect pests is often environmentally friendly and suitable for sustainable development of agricultural industries. However, this strategy can be limited by rapid evolution of insect populations that overcome HPR, for which the underlying molecular factors and mechanisms are not well understood. To address this issue, we analyzed transcriptomes of two distinct biotypes of the grain aphid, Sitobion avenae (Fabricius), on wheat and barley. This analysis revealed a large number of differentially expressed genes (DEGs) between biotypes 1 and 3 on wheat and barley. The majority of them were common DEGs occurring on both wheat and barley. GO and KEGG enrichment analyses for these common DEGs demonstrated significant expression divergence between both biotypes in genes associated with digestion and defense. Top defense-related common DEGs with the most significant expression changes included three peroxidases, two UGTs (UDP-glycosyltransferase), two cuticle proteins, one glutathione S-transferases (GST), one superoxide dismutase, and one esterase, suggesting their potentially critical roles in the divergence of S. avenae biotypes. A relatively high number of specific DEGs on wheat were identified for peroxidases (9) and P450s (8), indicating that phenolic compounds and hydroxamic acids may play key roles in resistance of wheat against S. avenae. Enrichment of specific DEGs on barley for P450s and ABC transporters suggested their key roles in this aphid's detoxification against secondary metabolites (e.g., alkaloids) in barley. Our results can provide insights into the molecular factors and functions that explain biotype adaptation in insects and their use of resistant plants. This study also has significant implications for developing new resistant cultivars, developing strategies that limit rapid development of insect biotypes, and extending resistant crop cultivars' durability and sustainability in integrated management programs.

Antinutrients in Plant-based Foods: A Review

Modern society has easy access to a vast informational database. The pursuit of sustainable green and healthy lifestyle leads to a series of food choices. Therefore, it is of importance to provide reliable, comprehensive and up-to-date information about food content including both nutritional and antinutritional elements.

Nutrients are associated with positive effects on human health. Antinutrients, on the other hand, are far less popular for the contemporary man. They are highly bioactive, capable of deleterious effects as well as some beneficial health effects in man, and vastly available in plant-based foods. These compounds are of natural or synthetic origin, interfere with the absorption of nutrients, and can be responsible for some mischievous effects related to the nutrient absorption. Some of the common symptoms exhibited by a large amount of antinutrients in the body can be nausea, bloating, headaches, rashes, nutritional deficiencies, etc. Phytates, oxalates, and lectins are few of the well-known antinutrients.

Science has acknowledged several ways in order to alter the negative influence antinutrients exhibiting on human health. Mechanical, thermal and biochemical approaches act synergistically to provide food with lower antinutritional levels.

The purpose of this review was to synthesize the availability of antinutrients, clear their effect on the human body, and commemorate possible paths to disable them. This review provides links to the available literature as well as enables a systematic view of the recently published research on the topic of plant-based antinutrients.

Purification and characterization of Bowman-Birk and Kunitz isoinhibitors from the seeds of Rhynchosia sublobata (Schumach.) Meikle, a wild relative of pigeonpea

Rhynchosia sublobata, a wild relative of pigeonpea, possesses defensive proteinase/protease inhibitors (PIs). Characterization of trypsin specific PIs (RsPI) separated from seeds by column chromatography using 2-D gel electrophoresis and Edman degradation method identified R. sublobata possessed both Bowman-Birk isoinhibitors (RsBBI) and Kunitz isoinhibitors (RsKI). A quick method was developed to separate RsBBI and RsKI from RsPI based on their differential solubility in TCA and acetate buffer. N-terminus sequencing of RsBBI and RsKI by MALDI-ISD ascertained the presence of Bowman Birk and Kunitz type isoinhibitors in R. sublobata. RsBBI (9216 Da) and RsKI (19,412 Da) exhibited self-association pattern as revealed by western blotting with anti-BBI antibody and MALDI-TOF peptide mass fingerprint analysis, respectively. RsBBI and RsKI varied significantly in their biochemical, biophysical and insecticidal properties. RsBBI inhibited the activity of trypsin (Ki = 128.5 ± 4.5 nM) and chymotrypsin (Ki = 807.8 ± 23.7 nM) while RsKI (Ki = 172.0 ± 9.2 nM) inhibited the activity of trypsin alone, by non-competitive mode. The trypsin inhibitor (TI) and chymotrypsin inhibitor (CI) activities of RsBBI were stable up to 100 °C. But, RsBBI completely lost its TI and CI activities on reduction with 3 mM DTT. Conversely, RsKI lost its TI activity on heating at 100 °C and retained >60% of its TI activity in presence of 3 mM DTT. CD spectroscopic studies on RsBBI and RsKI showed their secondary structural elements in the following order: random coils > β-sheets/β-turns > α-helix. However, RsKI showed reversible denaturation midpoint (Tm) of 75 °C. Further, the significant inhibitory activity of RsBBI (IC₅₀ = 24 ng) and RsKI (IC₅₀ = 59 ng) against trypsin-like gut proteases of Achaea janata (AjGPs) and Helicoverpa armigera (HaGPs) suggest them as potential biomolecules in the management of A. janata and H. armigera, respectively.

Transcriptional Responses in Defense-Related Genes of Sitobion avenae (Hemiptera: Aphididae) Feeding on Wheat and Barley

Many aphids can adapt on plants of differential resistance levels, but molecular interactions underlying host plant utilization and shift of aphids are still not well understood. Here, we sequenced the transcriptome and compared global gene expression profiles of Sitobion avenae (Fabricius) feeding on wheat (i.e., the susceptible plant) and barley (i.e., the resistant plant). In total, 65,200 high-quality unigenes were identified from the merged transcriptomes, and 861 of them were differentially expressed. Relative to their expression on barley, all differentially expressed P450 (cytochrome 450 monooxygenase) genes (e.g., SavCYP6A13, SavCYP4C1, and SavCYP4G15) in S. avenae on wheat were upregulated, suggesting the significance of P450s in xenobiotic metabolism for this aphid on wheat. For S. avenae on barley, some genes encoding for ATP-binding cassette (ABC) transporters (e.g., ABCG1, ABCG4, ABCB7, and ABCA5) and UDP-glucuronosyltransferases (UGTs; e.g., UGT2B1 and UGT2C1) showed a dramatic increase in expression, suggesting that ABC transporters and UGTs could be critical for detoxification metabolism in S. avenae on barley. In addition, the expression for nearly all differentially expressed proteases was upregulated for S. avenae on barley, reflecting xenobiotic challenges facing S. avenae on resistant barley. Thus, various detoxification and other defense-related genes (e.g., proteases and oxidases) showed highly inducible transcript regulation, suggesting great adaptive potential for S. avenae on different plants. All the abovementioned genes will be prime candidates for further studies of molecular interactions underlying host plant use and specialization in this aphid. Our results provide insights into aphids' defenses against variable phytochemicals, and the molecular basis underlying aphid-plant interactions as well.

Overexpression of the aphid-induced serine protease inhibitor CI2c gene in barley affects the generalist green peach aphid, not the specialist bird cherry-oat aphid

Aphids are serious pests in crop plants. In an effort to identify plant genes controlling resistance against aphids, we have here studied a protease inhibitor, CI2c in barley (Hordeum vulgare L.). The CI2c gene was earlier shown to be upregulated by herbivory of the bird cherry-oat aphid (Rhopalosiphum padi L.) in barley genotypes with moderate resistance against this aphid, but not in susceptible lines. We hypothesized that CI2c contributes to the resistance. To test this idea, cDNA encoding CI2c was overexpressed in barley and bioassays were carried out with R. padi. For comparison, tests were carried out with the green peach aphid (Myzus persicae Sulzer), for which barley is a poor host. The performance of R. padi was not different on the CI2c-overexpressing lines in comparison to controls in test monitoring behavior and fecundity. M. persicae preference was affected as shown in the choice test, this species moved away from control plants, but remained on the CI2c-overexpressing lines. R. padi-induced responses related to defense were repressed in the overexpressing lines as compared to in control plants or the moderately resistant genotypes. A putative susceptibility gene, coding for a β-1,3-glucanase was more strongly induced by aphids in one of the CI2c-overexpressing lines. The results indicate that the CI2c inhibitor in overexpressing lines affects aphid-induced responses by suppressing defense. This is of little consequence to the specialist R.padi, but causes lower non-host resistance towards the generalist M. persicae in barley.

Overexpression and Down-Regulation of Barley Lipoxygenase LOX2.2 Affects Jasmonate-Regulated Genes and Aphid Fecundity

Aphids are pests on many crops and depend on plant phloem sap as their food source. In an attempt to find factors improving plant resistance against aphids, we studied the effects of overexpression and down-regulation of the lipoxygenase gene LOX2.2 in barley (Hordeum vulgare L.) on the performance of two aphid species. A specialist, bird cherry-oat aphid (Rhopalosiphum padi L.) and a generalist, green peach aphid (Myzus persicae Sulzer) were studied. LOX2.2 overexpressing lines showed up-regulation of some other jasmonic acid (JA)-regulated genes, and antisense lines showed down-regulation of such genes. Overexpression or suppression of LOX2.2 did not affect aphid settling or the life span on the plants, but in short term fecundity tests, overexpressing plants supported lower aphid numbers and antisense plants higher aphid numbers. The amounts and composition of released volatile organic compounds did not differ between control and LOX2.2 overexpressing lines. Up-regulation of genes was similar for both aphid species. The results suggest that LOX2.2 plays a role in the activation of JA-mediated responses and indicates the involvement of LOX2.2 in basic defense responses.

The Protease Inhibitor CI2c Gene Induced by Bird Cherry-Oat Aphid in Barley Inhibits Green Peach Aphid Fecundity in Transgenic Arabidopsis

Aphids are phloem feeders that cause large damage globally as pest insects. They induce a variety of responses in the host plant, but not much is known about which responses are promoting or inhibiting aphid performance. Here, we investigated whether one of the responses induced in barley by the cereal aphid, bird cherry-oat aphid (Rhopalosiphum padi L.) affects aphid performance in the model plant Arabidopsis thaliana L. A barley cDNA encoding the protease inhibitor CI2c was expressed in A. thaliana and aphid performance was studied using the generalist green peach aphid (Myzus persicae Sulzer). There were no consistent effects on aphid settling or preference or on parameters of life span and long-term fecundity. However, short-term tests with apterous adult aphids showed lower fecundity on three of the transgenic lines, as compared to on control plants. This effect was transient, observed on days 5 to 7, but not later. The results suggest that the protease inhibitor is taken up from the tissue during probing and weakly inhibits fecundity by an unknown mechanism. The study shows that a protease inhibitor induced in barley by an essentially monocot specialist aphid can inhibit a generalist aphid in transgenic Arabidopsis.