Characterization of endogenous and recombinant forms of laccase-2, a multicopper oxidase from the tobacco hornworm, Manduca sexta

Multicopper oxidase-2 mediated cuticle formation: Its contribution to evolution and success of insects as terrestrial organisms

The insect cuticle is a non-cellular matrix composed of polysaccharide chitins and proteins. The cuticle covers most of the body surface, including the trachea, foregut, and hindgut, and it is the body structure that separates the intraluminal environment from the external environment. The cuticle is essential to sustain their lives, both as a physical barrier to maintain homeostasis and as an exoskeleton that mechanically supports body shape and movement. Previously, we proposed a theory about the possibility that the cuticle-forming system contributes to the "evolution and success of insects." The main points of our theory are that 1) insects evolved an insect-specific system of cuticle formation and 2) the presence of this system may have provided insects with a competitive advantage in the early land ecosystems. The key to this theory is that insects utilize molecular oxygen abundant in the atmosphere, which differs from closely related crustaceans that form their cuticles with calcium ions. With newly obtained knowledge, this review revisits the significance of the insect-specific system for insects to adapt to terrestrial environments and also discusses the long-standing question in entomology as to why, despite their great success in terrestrial environments, they poorly adapt to marine environments.

Proteomic investigation reveals the role of bacterial laccase from Bacillus pumilus in oxidative stress defense

The wide distribution of laccases in nature makes them involved in different biological processes. However, little information is known about how laccase participates in the defense machinery of bacteria against oxidative stress. The present study aimed to elucidate the oxidative stress response mechanism of Bacillus pumilus ZB1 and the functional role of bacterial laccase in stress defense. The oxidative stress caused by methyl methanesulfonate (MMS) significantly induced laccase activity and its transcript level. The morphological analysis revealed that the defense of B. pumilus ZB1 against oxidative stress was activated. Based on the proteomic study, 114 differentially expressed proteins (DEPs) were up-regulated and 79 DEPs were down-regulated. In COG analysis, 66.40% DEPs were classified into the category "Metabolism". We confirmed that laccase was up-regulated in response to MMS stress and its functional annotation was related to "Secondary metabolites biosynthesis, transport and catabolism". Based on protein-protein interaction prediction, two up-regulated DEPs (YcnJ and GabP) showed interaction with laccase and contributed to the formation of laccase stability and adaptability. The overexpressed laccase might improve the antioxidative property of B. pumilus ZB1. These findings provide an insight and the guidelines for better exploitation of bioremediation using bacterial laccase. SIGNIFICANCE: Bacillus pumilus is a gram-positive bacterium that has the potential for many applications, such as bioremediation. The expression of bacterial laccase is significantly influenced by oxidative stress, while the underlying mechanism of laccase overexpression in bacteria has not been fully studied. Elucidation of the biological process may benefit the bioremediation using bacteria in the future. In this study, the differentially expressed proteins were analyzed using a TMT-labeling proteomic approach when B. pumilus was treated with methyl methanesulfonate (MMS). Reactive oxygen species induced by MMS activated the secondary metabolites biosynthesis, transport, and catabolism in B. pumilus, including laccase overexpression. Moreover, the simultaneously up-regulated YcnJ and GabP may benefit the synthesis and the stability of laccase, then improve the antioxidative property of B. pumilus against environmental stress. Our findings advance the understanding of the adaptive mechanism of B. pumilus to environmental conditions.

A Review on Digestive System of Rhynchophorus ferrugineus as Potential Target to Develop Control Strategies

Rhynchophorus ferrugineus, commonly known as red palm weevil (RPW), is a high-risk insect pest that has become a threat to many important palm species. There are several dominant factors that lead to the successful infestation of RPW, including its stealthy lifestyle, highly chitinized mouthpart, and high fecundity rate. Due to that, millions of dollars of losses have been suffered by many countries invaded by RPW. Several methods have been designed to control its invasion, including the usage of insecticides, but many cause resistance and environmental pollution. Therefore, an environmentally friendly insecticide that targets specific systems or pathways in RPW is urgently needed. One of the potential targets is the digestive system of RPW, as it is the major interface between the insect and its plant host. The related knowledge of RPW's digestive system, such as the anatomy, microflora, transcriptomic analysis, and proteomic analysis, is important to understand its effects on RPW's survival. Several data from different omics regarding the digestive systems of RPW have been published in separate reports. Some of the potential targets have been reported to be inhibited by certain potential insecticides, while other targets have not yet been tested with any inhibitors. Hence, this review may lead to a better understanding on managing infestations of RPW using the system biology approach for its digestive system.

Characterization of five pigmentation genes as transgenic markers in Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm, Spodoptera frugiperda (J. E. Smith), has become one of the most damaging pests worldwide since its invasion of Africa, Asia and Oceania from 2016, threatening plants in 76 families including important crops. Genetics-based methods have proved to be an efficient way to control pests, especially invasive species, but many difficulties must be overcome to develop a transgenic insect strain, especially for a non-model species. Here we thus sought to identify a visible marker that would facilitate the distinction between genetically modified (GM) and non-transgenic insects, thereby simplifying mutation identification and facilitating the broader application of genome editing tools in non-model insects. Five genes (sfyellow-y, sfebony, sflaccase2, sfscarlet, and sfok) that are orthologs of well-studied genes in pigment metabolism were knocked out using the CRISPR/Cas9 system to identify candidate gene markers. Two genes, Sfebony and Sfscarlet, were identified responsible for body and compound eye coloration, respectively, in S. frugiperda, and could be potential visual markers for genetics-based pest management strategies.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Laccase: Various types and applications

Laccase belongs to the polyphenol oxidase family and is very important in removing environmental pollutants due to its structural and functional properties. Recently, the ability of laccase to oxidize phenolic and nonphenolic substances has been considered by many researchers. This enzyme's application scope includes a broad range of chemical processes and industrial usages, such as bioremediation, nanobiotechnology, woodworking industries, bleaching of paper pulp, dyeing in the textile industry, biotechnological uses in food industries, biorefining, detoxification from wastewater, production of organic matter from phenolic and amine substrates, and biofuels. Although filamentous fungi produce large amounts of laccase, high-yield industrial-scale production of laccase is still faced with many problems. At present, researchers are trying to increase the efficiency and productivity and reduce the final price of laccase by finding suitable microorganisms and improving the process of production and purification of laccase. This article reviews the introduction of laccase, its properties, production processes, and the effect of various factors on the enzyme's stability and activity, and some of its applications in various industries.

Involvement of Laccase2 in Cuticle Sclerotization of the Whitefly, Bemisia tabaci Middle East–Asia Minor 1

Cuticle sclerotization is critical for insect survival. Laccase2 (Lac2) is a phenol oxidase that plays a key role in cuticle formation and pigmentation in a variety of insects. However, the function of Lac2 in whitefly, Bemisia tabaci, remains unclear. In this study, we identified a BtLac2 gene in B. tabaci MEAM1 and found that BtLac2 was expressed in all stages. It was highly expressed in the egg stage, followed by nymph and adult. Moreover, the expression of BtLac2 was higher in the cuticle than in other tissues. Knockdown of BtLac2 in nymphs produced thinner and fragile cuticles, which significantly increased the mortality rate, extended the development duration of nymphs, and decreased the emergence rate of adults. This result demonstrates that BtLac2 plays an important role in the cuticle hardening of B. tabaci and suggests a potential management strategy using RNAi to knock down BtLac2 expression.

Integrated miRNA and transcriptome profiling to explore the molecular determinism of convergent adaptation to corn in two lepidopteran pests of agriculture

Background

The degree to which adaptation to same environment is determined by similar molecular mechanisms, is a topic of broad interest in evolutionary biology, as an indicator of evolutionary predictability. We wished to address if adaptation to the same host plant in phytophagous insects involved related gene expression patterns. We compared sRNA-Seq and RNA-Seq data between two pairs of taxa of Ostrinia and Spodoptera frugiperda sharing maize as host-plant. For the latter, we had previously carried out a reciprocal transplant experiment by feeding of the larvae of the Corn strain (Sf-C) and the Rice strain (Sf-R) on corn versus rice and characterized the mRNA and miRNA responses.

Results

First, we predicted the genes encoding miRNA in Ostrinia nubilalis (On) and O. scapulalis (Os). Respectively 67 and 65 known miRNA genes, as well as 196 and 190 novel ones were predicted with Os genome using sncRNAs extracted from whole larvae feeding on corn or mugwort. In On, a read counts analysis showed that 37 (55.22%) known miRNAs and 19 (9.84%) novel miRNAs were differentially expressed (DE) on mugwort compared to corn (in Os, 25 known miRs (38.46%) and 8 novel ones (4.34%)). Between species on corn, 8 (12.5%) known miRNAs and 8 (6.83%) novel ones were DE while only one novel miRNA showed expression variation between species on mugwort. Gene target prediction led to the identification of 2953 unique target genes in On and 2719 in Os, among which 11.6% (344) were DE when comparing species on corn. 1.8% (54) of On miR targets showed expression variation upon a change of host-plant.

We found molecular changes matching convergent phenotype, i.e., a set of nine miRNAs that are regulated either according to the host-plant both in On and Sf-C or between them on the same plant, corn. Among DE miR target genes between taxa, 13.7% shared exactly the same annotation between the two pairs of taxa and had function related to insect host-plant interaction.

Conclusion

There is some similarity in underlying genetic mechanisms of convergent evolution of two distant Lepidopteran species having adopted corn in their host range, highlighting possible adaptation genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07905-7.

Multifunctional role of a fungal pathogen-secreted laccase 2 in evasion of insect immune defense

Laccases are widely present in bacteria, fungi, plants and invertebrates and involved in a variety of physiological functions. Here, we report that Beauveria bassiana, an economic important entomopathogenic fungus, secretes a laccase 2 (BbLac2) during infection that detoxifies insect immune response-generated reactive oxygen species (ROS) and interferes with host immune phenoloxidase (PO) activation. BbLac2 is expressed in fungal cells during proliferation in the insect haemocoel and can be found to distribute on the surface of haemolymph-derived in vivo fungal hyphal bodies or be secreted. Targeted gene-knockout of BbLac2 increased fungal sensitivity to oxidative stress, decreased virulence to insect, and increased host PO activity. Strains overexpressing BbLac2 showed increased virulence, with reduced host PO activity and lowered ROS levels in infected insects. In vitro assays revealed that BbLac2 could eliminate ROS and oxidize PO substrates (phenols), verifying the enzymatic functioning of the protein in detoxification of cytotoxic ROS and interference with the PO cascade. Moreover, BbLac2 acted as a cell surface protein that masked pathogen associated molecular patterns (PAMPs), enabling the pathogen to evade immune recognition. Our data suggest a multifunctional role for fungal pathogen-secreted laccase 2 in evasion of insect immune defenses.

RNAi-Mediated Suppression of Laccase2 Impairs Cuticle Tanning and Molting in the Cotton Boll Weevil (Anthonomus grandis)

The cotton boll weevil, Anthonomus grandis, is the most economically important pest of cotton in Brazil. Pest management programs focused on A. grandis are based mostly on the use of chemical insecticides, which may cause serious ecological impacts. Furthermore, A. grandis has developed resistance to some insecticides after their long-term use. Therefore, alternative control approaches that are more sustainable and have reduced environmental impacts are highly desirable to protect cotton crops from this destructive pest. RNA interference (RNAi) is a valuable reverse genetics tool for the investigation of gene function and has been explored for the development of strategies to control agricultural insect pests. This study aimed to evaluate the biological role of the Laccase2 (AgraLac2) gene in A. grandis and its potential as an RNAi target for the control of this insect pest. We found that AgraLac2 is expressed throughout the development of A. grandis with significantly higher expression in pupal and adult developmental stages. In addition, the immunolocalization of the AgraLac2 protein in third-instar larvae using specific antibodies revealed that AgraLac2 is distributed throughout the epithelial tissue, the cuticle and the tracheal system. We also verified that the knockdown of AgraLac2 in A. grandis resulted in an altered cuticle tanning process, molting defects and arrested development. Remarkably, insects injected with dsAgraLac2 exhibited defects in cuticle hardening and pigmentation. As a consequence, the development of dsAgraLac2-treated insects was compromised, and in cases of severe phenotypic defects, the insects subsequently died. On the contrary, insects subjected to control treatments did not show any visible phenotypic defects in cuticle formation and successfully molted to the pupal and adult stages. Taken together, our data indicate that AgraLac2 is involved in the cuticle tanning process in A. grandis and may be a promising target for the development of RNAi-based technologies.

Laccase Properties, Physiological Functions, and Evolution

Discovered in 1883, laccase is one of the first enzymes ever described. Now, after almost 140 years of research, it seems that this copper-containing protein with a number of unique catalytic properties is widely distributed across all kingdoms of life. Laccase belongs to the superfamily of multicopper oxidases (MCOs)—a group of enzymes comprising many proteins with different substrate specificities and diverse biological functions. The presence of cupredoxin-like domains allows all MCOs to reduce oxygen to water without producing harmful byproducts. This review describes structural characteristics and plausible evolution of laccase in different taxonomic groups. The remarkable catalytic abilities and broad substrate specificity of laccases are described in relation to other copper-containing MCOs. Through an exhaustive analysis of laccase roles in different taxa, we find that this enzyme evolved to serve an important, common, and protective function in living systems.

Molecular Insights into the Insensitivity of Lepidopteran Pests to Cycloxaprid

Cycloxaprid (CYC) is effective in the control of hemipteran pests, but its bioactivity against lepidopteran pests is still unclear. Here, the bioactivity of CYC against lepidopteran pests was found to be much worse than that against hemipteran insects. To reveal the mechanism, the transcriptomes of CYC-treated and untreated Ostrinia furnacalis larvae were compared. Among the top 20 differentially expressed genes, 11 encode proteins involved in cuticle formation, while only one encodes a detoxifying enzyme. Thus, the cuticle appears to be important for the insensitivity of O. furnacalis to CYC. A pretreatment of O. furnacalis larvae with methoprene enhanced the bioactivity of CYC by 1.12-fold. Moreover, mixtures of CYC with graphene oxide increased the bioactivity of CYC by 1.88-fold. Because lepidopteran and hemipteran insects often harm crops at the same time, the work can help make full use of CYC and reduce the environmental impacts of using multiple pesticides.

Mini-review an insect-specific system for terrestrialization: Laccase-mediated cuticle formation

Insects are often regarded as the most successful group of animals in the terrestrial environment. Their success can be represented by their huge biomass and large impact on ecosystems. Among the factors suggested to be responsible for their success, we focus on the possibility that the cuticle might have affected the process of insects' evolution. The cuticle of insects, like that of other arthropods, is composed mainly of chitin and structural cuticle proteins. However, insects seem to have evolved a specific system for cuticle formation. Oxidation reaction of catecholamines catalyzed by a copper enzyme, laccase, is the key step in the metabolic pathway for hardening of the insect cuticle. Molecular phylogenetic analysis indicates that laccase functioning in cuticle sclerotization has evolved only in insects. In this review, we discuss a theory on how the insect-specific "laccase" function has been advantageous for establishing their current ecological position as terrestrial animals.

Laccase 1 gene from Plutella xylostella (PxLac1) and its functions in humoral immune response

Laccase (EC 1.10.3.2) is a phenoloxidase found in many insect species. The Laccase 1 gene from Plutella xylostella (PxLac1) was cloned, and its expression patterns and functions were determined using qPCR and RNAi methods. The results showed that the expression levels of PxLac1 were consistently high in all larval stages, and the most abundant was in the midgut during the 4th instar stage. Moreover, the expression of PxLac1 was up-regulated in response to bacterial infection, and decreased 24 h after being parasitized by Cotesia vestalis. Further analyses indicated that the effect of parasitization on PxLac1 was induced by active C. vestalis Bracovirus (CvBV). Haemocyte-free hemolymph phenoloxidase (PO) activity was suppressed when PxLac1 was treated with RNAi. Our results provide evidence for a connection between the Laccase 1 gene and insect immunity, and revealed that parasitoid polydnavirus suppresses host PO activity via PxLac1 regulation.

Identification and characterization of a laccase from Litopenaeus vannamei involved in anti-bacterial host defense

Phenoloxidases (POs) are a family of enzymes including tyrosinases, catecholases and laccases, which play an important role in immune defences of various invertebrates. Whether or not laccase exists in shrimp and its function is still poorly understood. In this study, a laccase (LvLac) was cloned and identified from Litopenaeus vannamei for the first time. The full length of LvLac is 3406 bp, including a 2034 bp open reading frame (ORF) coding for a putative protein of 677 amino acids with a signal peptide of 33 aa. LvLac contains three Cu-oxidase domains with copper binding centers formed by 10 histidines, one cysteine and one methionine, respectively. Phylogenetic analysis revealed that LvLac was close to insects laccase 1 family. LvLac expression was most abundant in heart and the crude LvLac protein could catalyze the oxidation of hydroquinone. Real-time PCR showed that LvLac expression was responsive to Vibrio parahaemolyticus, Micrococcus lysodeikticus and white spot syndrome virus (WSSV) infection. Knockdown of LvLac enhanced the sensitivity of shrimps to V. parahaemolyticus and M. lysodeikticus challenge, suggesting that LvLac may play a positive role against bacterial pathogens.

Multiple resistance to pirimiphos-methyl and bifenthrin in Tribolium castaneum involves the activity of lipases, esterases, and laccase2

Several recent studies have elucidated the molecular mechanisms that confer insecticide resistance on insect pests. However, little is known about multiple resistance in red flour beetle (Tribolium castaneum) at molecular level. The multiple resistance is characterized as resistance to different classes of insecticides that have different target sites, and is mediated by several enzymatic systems. In this study, we investigated the biochemical and molecular mechanisms involved in multiple resistance of T. castaneum to bifenthrin (pyrethroid [Pyr]) and pirimiphos-methyl (organophosphate [Org]). We used artificial selection, biochemical and in silico approaches including structural computational biology. After five generations of artificial selection in the presence of bifenthrin (F5Pyr) or pirimiphos-methyl (F5Org), we found high levels of multiple resistance. The hierarchical enzymatic cluster revealed a pool of esterases (E), lipases (LIPs) and laccase2 (LAC2) potentially contributing to the resistance in different ways throughout development, after one or more generations in the presence of insecticides. The enzyme-insecticide interaction network indicated that E2, E3, LIP3, and LAC2 are enzymes potentially required for multiple resistance phenotype. Kinetic analysis of esterases from F5Pyr and F5Org showed that pirimiphos-methyl and specially bifenthrin promote enzyme inhibition, indicating that esterases mediate resistance by sequestering bifenthrin and pirimiphos-methyl. Our computational data were in accordance with kinetic results, indicating that bifenthrin has higher affinity at the active site of esterase than pirimiphos-methyl. We also report the capability of these insecticides to modify the development in T. castaneum. Our study provide insights into the biochemical mechanisms employed by T. castaneum to acquire multiple resistance.

Suppression of Laccase 2 severely impairs cuticle tanning and pathogen resistance during the pupal metamorphosis of Anopheles sinensis (Diptera: Culicidae)

Background

Phenol oxidases (POs) catalyze the oxidation of dopa and dopamine to melanin, which is crucial for cuticle formation and innate immune maintenance in insects. Although, Laccase 2, a member of the PO family, has been reported to be a requirement for melanin-mediated cuticle tanning in the development stages of some insects, whether it participates in cuticle construction and other physiological processes during the metamorphosis of mosquito pupae is unclear.

Methods

The association between the phenotype and the expression profile of Anopheles sinensis Laccase 2 (AsLac2) was assessed from pupation to adult eclosion. Individuals showing an expression deficiency of AsLac2 that was produced by RNAi and their phenotypic defects and physiological characterizations were compared in detail with the controls.

Results

During the dominant expression period, knockdown of AsLac2 in pupae caused the cuticle to be unpigmented, and produced thin and very soft cuticles, which further impeded the eclosion rate of adults as well as their fitness. Moreover, melanization immune responses in the pupae were sharply decreased, leading to poor resistance to microorganism infection. Both the high conservation among Laccase 2 homologs and a very similar genomic synteny of the neighborhood in Anopheles genus implies a conservative function in the pupal stage.

Conclusions

To our knowledge, this is the first study to report the serious phenotypic defects in mosquito pupae caused by the dysfunction of Laccase 2. Our findings strongly suggest that Laccase 2 is crucial for Anopheles cuticle construction and melanization immune responses to pathogen infections during pupal metamorphosis. This irreplaceability provides valuable information on the application of Lacccase 2 and/or other key genes in the melanin metabolism pathway for developing mosquito control strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2118-4) contains supplementary material, which is available to authorized users.

Yeast Hosts for the Production of Recombinant Laccases: A Review

Laccases are multi-copper oxidoreductases which catalyze the oxidation of a wide range of substrates during the simultaneous reduction of oxygen to water. These enzymes, originally found in fungi, plants, and other natural sources, have many industrial and biotechnological applications. They are used in the food, textile, pulp, and paper industries, as well as for bioremediation purposes. Although natural hosts can provide relatively high levels of active laccases after production optimization, heterologous expression can bring, moreover, engineered enzymes with desired properties, such as different substrate specificity or improved stability. Hence, diverse hosts suitable for laccase production are reviewed here, while the greatest emphasis is placed on yeasts which are commonly used for industrial production of various proteins. Different approaches to optimize the laccase expression and activity are also discussed in detail here.

Critical Analysis of the Melanogenic Pathway in Insects and Higher Animals

Animals synthesize melanin pigments for the coloration of their skin and use it for their protection from harmful solar radiation. Insects use melanins even more ingeniously than mammals and employ them for exoskeletal pigmentation, cuticular hardening, wound healing and innate immune responses. In this review, we discuss the biochemistry of melanogenesis process occurring in higher animals and insects. A special attention is given to number of aspects that are not previously brought to light: (1) the molecular mechanism of dopachrome conversion that leads to the production of two different dihydroxyindoles; (2) the role of catecholamine derivatives other than dopa in melanin production in animals; (3) the critical parts played by various biosynthetic enzymes associated with insect melanogenesis; and (4) the presence of a number of important gaps in both melanogenic and sclerotinogenic pathways. Additionally, importance of the melanogenic process in insect physiology especially in the sclerotization of their exoskeleton, wound healing reactions and innate immune responses is highlighted. The comparative biochemistry of melanization with sclerotization is also discussed.

High Level Secretion of Laccase (LccH) from a Newly Isolated White-Rot Basidiomycete, Hexagonia hirta MSF2

Newer and novel laccases attract considerable attention due to its promising and valuable multiple applications in biotech industry. This present investigation documents, for the first time, on high level extracellular secretion of laccase (LccH) in newly isolated wood-degrading basidiomycete Hexagonia hirta MSF2. LccH was optimally active at 40°C in citrate phosphate buffer with a pH of 3.4. Optimized Cu(2+) in glucose yeast extract (GY) medium enhanced the LccH production by H. hirta to 1944.44 U.ml(-1). A further increment in LccH activity of 5671.30 U.ml(-1) was achieved by the addition of a phenolic inducer, 2,5 Xylidine. Zymogram and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of LccH revealed that LccH is a monomer with a molecular mass of 66 kDa. MALDI-TOF-MS based peptide mass fingerprinting and comparative modeling of the amino acid sequence of LccH showed that it was closer to Trametes sp. AH28-2 (PDB: 3KW7) with 48% identity, 95% coverage, 0.011 alignment score and RMSD of 0.497Å. Crude LccH delignified lignocellulosic biomass such as wood and corncob, to a level of 28.6 and 16.5%, respectively. Such high level secretion, thermal and solvent stability of LccH make H. hirta a potential candidate not only for LccH production and biodelignification but also generation of lignin derived aromatic feed stock chemicals for industrial and environmental applications.

Comparative Analysis of Transcriptomes among Bombyx mori Strains and Sexes Reveals the Genes Regulating Melanic Morph and the Related Phenotypes

As a source of insect polymorphism, melanism plays an important role in ecological adaption and usually endows advantageous phenotypic-effects on insects. However, due to the mechanistic diversity, there are knowledge gaps in the molecular mechanisms underlying melanism and the related phenotypes. In silk moths, a recessive melanic mutant (sex-controlled melanism, sml) strain exhibits extended adult longevity. We took a transcriptome approach to perform a comparative analysis between this sml strain and a wild-type strain (Dazao). Our analysis resulted in the identification of 59 unique differentially expressed genes in the melanic mutant. Two key genes (laccase2 and yellow) involved in melanin formation were significantly up-regulated in melanic individuals. The laccase2 B-type isoform (BGIBMGA006746) was found to likely participate in the silkworm cuticular melanism process at late pupal stage. Moreover, we discovered 22 cuticular protein encoding genes with the possible function in melanin transport and/or maintenance. Based on our findings, we presume that the longer survival of the melanic sml male moths might be associated with the enhanced antioxidant defense systems and a reduction in the insulin/IGF-1 signaling pathway (IIS). These findings will facilitate the understanding of the molecular basis underlying melanism and the derived phenotypic-effects.

MicroRNA857 Is Involved in the Regulation of Secondary Growth of Vascular Tissues in Arabidopsis

MicroRNAs (miRNAs) are endogenous small RNAs that repress target gene expression posttranscriptionally, and are critically involved in various developmental processes and responses to environmental stresses in eukaryotes. MiRNA857 is not widely distributed in plants and is encoded by a single gene, AtMIR857, in Arabidopsis (Arabidopsis thaliana). The functions of miR857 and its mechanisms in regulating plant growth and development are still unclear. Here, by means of genetic analysis coupled with cytological studies, we investigated the expression pattern and regulation mechanism of miR857 and its biological functions in Arabidopsis development. We found that miR857 regulates its target gene, Arabidopsis LACCASE7, at the transcriptional level, thereby reducing laccase activity. Using stimulated Raman scattering and x-ray microtomography three-dimensional analyses, we showed that miR857 was involved in the regulation of lignin content and consequently morphogenesis of the secondary xylem. In addition, miR857 was activated by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7 in response to low copper conditions. Collectively, these findings demonstrate the role of miR857 in the regulation of secondary growth of vascular tissues in Arabidopsis and reveal a unique control mechanism for secondary growth based on the miR857 expression in response to copper deficiency.

The multicopper oxidase gene family in the brown planthopper, Nilaparvata lugens

The multicopper oxidase (MCO) family of enzymes includes laccases, ascorbate oxidases, bilirubin oxidases and a subgroup of metal oxidases. On the basis of a bioinformatics investigation, we identified 7 genes encoding putative multicopper oxidase proteins in the genome of the brown planthopper (BPH), Nilaparvata lugens (Hemiptera: Delphacidae). MCO1 and MCO2 are conserved, while others diverse in insects. Analysis of developmental and tissue-specific expression patterns revealed the following: NlMCO2 was mainly expressed in the integument, and its expression peaked periodically during molting; NlMCO3 was an ovary-specific MCO gene with a high expression level only at the adult stage; NlMCO4 was a salivary gland-specific MCO gene that was expressed at all developmental stages; NlMCO5 only had short-term expression in the middle of the fourth instar stage and was expressed mainly in the gut; NlMCO6 had a developmental expression pattern similar to that of NlMCO2 and was expressed in most N. lugens tissues; and NlMCO1 was expressed in most N. lugens tissues except for the testis, whereas NlMCO7 was mainly expressed in the gut and the Malpighian tube. BPHs injected with double-stranded RNA (dsRNA) targeting NlMCO2 failed to pigment and sclerotize, were colorless and soft-bodied and subsequently died in a short time. Lethal phenotypes were also observed in insects challenged by dsRNA targeting NlMCO6. However, no observable morphological or internal structural abnormality was obtained in the insects treated with dsRNA for NlMCO1, NlMCO3, NlMCO4, NlMCO5 or NlMCO7.

Re-examination of a α-chymotrypsin-solubilized laccase in the pupal cuticle of the silkworm, Bombyx mori: Insights into the regulation system for laccase activation during the ecdysis process

The laccase in the pupal cuticle of the silkworm, Bombyx mori, is thought to accumulate as an inactive precursor that can be activated stage-dependently. In this study we isolated an 81-kDa laccase from cuticular extract of B. mori that was prepared by digestion of the pupal cuticles with α-chymotrypsin. The mass spectrometric analysis of the purified protein indicates that this 81-kDa laccase is a product of the Bombyx laccase2 gene. The purified 81-kDa laccase (α-chymotrypsin-solubilized Bombyx laccase2: Bm-clac2) has an N-terminal sequence of RNPADS that corresponds to Arg146 to Ser151 of the deduced protein sequence of Bmlaccase2 cDNA, indicating that Bm-clac2 lacks the N-terminal part upstream from residue Arg146. Bm-clac2 shows enzymatic activity, but its specific activity is increased around 17-fold after treatment with trypsin, which involves cleavage of peptide bonds at the C-terminal region. We also found that the activity of Bm-clac2 is increased in the presence of isopropanol. In previous reports, proteolytic processing has been hypothesized as a system for laccase activation in vivo, but the present result implies that this type of processing is not the only way to convert Bm-clac2 to the high-activity enzyme.

A multicopper oxidase-related protein is essential for insect viability, longevity and ovary development

Typical multicopper oxidases (MCOs) have ten conserved histidines and one conserved cysteine that coordinate four copper atoms. These copper ions are required for oxidase activity. During our studies of insect MCOs, we discovered a gene that we named multicopper oxidase-related protein (MCORP). MCORPs share sequence similarity with MCOs, but lack many of the copper-coordinating residues. We identified MCORP orthologs in many insect species, but not in other invertebrates or vertebrates. We predicted that MCORPs would lack oxidase activity due to the absence of copper-coordinating residues. To test this prediction, we purified recombinant Tribolium castaneum (red flour beetle) MCORP and analyzed its enzymatic activity using a variety of substrates. As expected, no oxidase activity was detected. To study MCORP function in vivo, we analyzed expression profiles of TcMCORP and Anopheles gambiae (African malaria mosquito) MCORP, and assessed RNAi-mediated knockdown phenotypes. We found that both MCORPs are constitutively expressed at a low level in all of the tissues we analyzed. Injection of TcMCORP dsRNA into larvae resulted in 100% mortality prior to adult eclosion, with death occurring mainly during the pharate pupal stage or late pharate adult stage. Injection of TcMCORP dsRNA into pharate pupae resulted in the death of approximately 20% of the treated insects during the pupal to adult transition and a greatly shortened life span for the remaining insects. In addition, knockdown of TcMCORP in females prevented oocyte maturation and, thus, greatly decreased the number of eggs laid. These results indicate that TcMCORP is an essential gene and that its function is required for reproduction. An understanding of the role MCORP plays in insect physiology may help to develop new strategies for controlling insect pests.

Effects of altered catecholamine metabolism on pigmentation and physical properties of sclerotized regions in the silkworm melanism mutant

Catecholamine metabolism plays an important role in the determination of insect body color and cuticle sclerotization. To date, limited research has focused on these processes in silkworm. In the current study, we analyzed the interactions between catecholamines and melanin genes and their effects on the pigmentation patterns and physical properties of sclerotized regions in silkworm, using the melanic mutant melanism (mln) silkworm strain as a model. Injection of β-alanine into mln mutant silkworm induced a change in catecholamine metabolism and turned its body color yellow. Further investigation of the catecholamine content and expression levels of the corresponding melanin genes from different developmental stages of Dazao-mln (mutant) and Dazao (wild-type) silkworm revealed that at the larval and adult stages, the expression patterns of melanin genes precipitated dopamine accumulation corresponding to functional loss of Bm-iAANAT, a repressive effect of excess NBAD on ebony, and upregulation of tan in the Dazao-mln strain. During the early pupal stage, dopamine did not accumulate in Dazao-mln, since upregulation of ebony and black genes led to conversion of high amounts of dopamine into NBAD, resulting in deep yellow cuticles. Scanning electron microscope analysis of a cross-section of adult dorsal plates from both wild-type and mutant silkworm disclosed the formation of different layers in Dazao-mln owing to lack of NADA, compared to even and dense layers in Dazao. Analysis of the mechanical properties of the anterior wings revealed higher storage modulus and lower loss tangent in Dazao-mln, which was closely associated with the altered catecholamine metabolism in the mutant strain. Based on these findings, we conclude that catecholamine metabolism is crucial for the color pattern and physical properties of cuticles in silkworm. Our results should provide a significant contribution to Lepidoptera cuticle tanning research.

Existence of prophenoloxidase in wing discs: a source of plasma prophenoloxidase in the silkworm, Bombyx mori

In insects, hemocytes are considered as the only source of plasma prophenoloxidase (PPO). PPO also exists in the hemocytes of the hematopoietic organ that is connected to the wing disc of Bombyx mori. It is unknown whether there are other cells or tissues that can produce PPO and release it into the hemolymph besides circulating hemocytes. In this study, we use the silkworm as a model to explore this possibility. Through tissue staining and biochemical assays, we found that wing discs contain PPO that can be released into the culture medium in vitro. An in situ assay showed that some cells in the cavity of wing discs have PPO1 and PPO2 mRNA. We conclude that the hematopoietic organ may wrongly release hemocytes into wing discs since they are connected through many tubes as repost in previous paper. In wing discs, the infiltrating hemocytes produce and release PPO probably through cell lysis and the PPO is later transported into hemolymph. Therefore, this might be another source of plasma PPO in the silkworm: some infiltrated hemocytes sourced from the hematopoietic organ release PPO via wing discs.

Enzyme activity demonstrates multiple pathways of innate immunity in Indo-Pacific anthozoans

Coral reefs are threatened by increasing levels of coral disease and the functional loss of obligate algal symbionts (bleaching). Levels of immunity relate directly to susceptibility to these threats; however, our understanding of fundamental aspects of coral immunology is lacking. We show that three melanin-synthesis pathway components (mono-phenoloxidase, ortho-diphenoloxidase (tyrosinase-type pathway) and para-diphenoloxidase (laccase-type pathway)) are present in both their active (phenoloxidase, PO) and inactive (prophenoloxidase, PPO) forms across a diverse range of 22 species of healthy Indo-Pacific anthozoans. We also demonstrate transglutaminase activity of the coagulation cascade for, to our knowledge, the first time in a coral. Melanin-synthesis enzyme activities varied among taxa, although they were generally lowest in the coral family Acroporidae and highest in the Poritidae and Oculinidae. Inactive tyrosinase-type activity (PPO) and active laccase-type activity (PO) correlate with taxonomic patterns in disease resistance, whereas the converse pattern in activity levels correlates with bleaching resistance. Overall, we demonstrate the presence of several melanin-synthesis pathways in Indo-Pacific corals, co-regulation among some pathway components, and highlight their potential roles in coral health.

Kinetic properties of alternatively spliced isoforms of laccase-2 from Tribolium castaneum and Anopheles gambiae

Laccase-2 is a highly conserved multicopper oxidase that functions in insect cuticle pigmentation and tanning. In many species, alternative splicing gives rise to two laccase-2 isoforms. A comparison of laccase-2 sequences from three orders of insects revealed eleven positions at which there are conserved differences between the A and B isoforms. Homology modeling suggested that these eleven residues are not part of the substrate binding pocket. To determine whether the isoforms have different kinetic properties, we compared the activity of laccase-2 isoforms from Tribolium castaneum and Anopheles gambiae. We partially purified the four laccases as recombinant enzymes and analyzed their ability to oxidize a range of laccase substrates. The predicted endogenous substrates tested were dopamine, N-acetyldopamine (NADA), N-β-alanyldopamine (NBAD) and dopa, which were detected in T. castaneum previously and in A. gambiae as part of this study. Two additional diphenols (catechol and hydroquinone) and one non-phenolic substrate (2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid)) were also tested. We observed no major differences in substrate specificity between the A and B isoforms. Dopamine, NADA and NBAD were oxidized with catalytic efficiencies ranging from 51 to 550 min⁻¹ mM⁻¹. These results support the hypothesis that dopamine, NADA and NBAD are endogenous substrates for both isoforms of laccase-2. Catalytic efficiencies associated with dopa oxidation were low, ranging from 8 to 30 min⁻¹ mM⁻¹; in comparison, insect tyrosinase oxidized dopa with a catalytic efficiency of 201 min⁻¹ mM⁻¹. We found that dopa had the highest redox potential of the four endogenous substrates, and this property of dopa may explain its poor oxidation by laccase-2. We conclude that laccase-2 splice isoforms are likely to oxidize the same substrates in vivo, and additional experiments will be required to discover any isoform-specific functions.

Hindgut innate immunity and regulation of fecal microbiota through melanization in insects

Many insects eat the green leaves of plants but excrete black feces in an as yet unknown mechanism. Insects cannot avoid ingesting pathogens with food that will be specifically detected by the midgut immune system. However, just as in mammals, many pathogens can still escape the insect midgut immune system and arrive in the hindgut, where they are excreted out with the feces. Here we show that the melanization of hindgut content induced by prophenoloxidase, a key enzyme that induces the production of melanin around invaders and at wound sites, is the last line of immune defense to clear bacteria before feces excretion. We used the silkworm Bombyx mori as a model and found that prophenoloxidase produced by hindgut cells is secreted into the hindgut contents. Several experiments were done to clearly demonstrate that the blackening of the insect feces was due to activated phenoloxidase, which served to regulate the number of bacteria in the hindgut. Our analysis of the silkworm hindgut prophenoloxidase discloses the natural secret of why the phytophagous insect feces is black and provides insight into hindgut innate immunity, which is still rather unclear in mammals.

Heterologous laccase production and its role in industrial applications

Laccases are blue multicopper oxidases, catalyzing the oxidation of an array of aromatic substrates concomitantly with the reduction of molecular oxygen to water. These enzymes are implicated in a variety of biological activities. Most of the laccases studied thus far are of fungal origin. The large range of substrates oxidized by laccases has raised interest in using them within different industrial fields, such as pulp delignification, textile dye bleaching, and bioremediation. Laccases secreted from native sources are usually not suitable for large-scale purposes, mainly due to low production yields and high cost of preparation/purification procedures. Heterologous expression may provide higher enzyme yields and may permit to produce laccases with desired properties (such as different substrate specificities, or improved stabilities) for industrial applications. This review surveys researches on heterologous laccase expression focusing on the pivotal role played by recombinant systems towards the development of robust tools for greening modern industry.

Ecdysteroid-dependent expression of the tweedle and peroxidase genes during adult cuticle formation in the honey bee, Apis mellifera

Cuticle renewal is a complex biological process that depends on the cross talk between hormone levels and gene expression. This study characterized the expression of two genes encoding cuticle proteins sharing the four conserved amino acid blocks of the Tweedle family, AmelTwdl1 and AmelTwdl2, and a gene encoding a cuticle peroxidase containing the Animal haem peroxidase domain, Ampxd, in the honey bee. Gene sequencing and annotation validated the formerly predicted tweedle genes, and revealed a novel gene, Ampxd, in the honey bee genome. Expression of these genes was studied in the context of the ecdysteroid-coordinated pupal-to-adult molt, and in different tissues. Higher transcript levels were detected in the integument after the ecdysteroid peak that induces apolysis, coinciding with the synthesis and deposition of the adult exoskeleton and its early differentiation. The effect of this hormone was confirmed in vivo by tying a ligature between the thorax and abdomen of early pupae to prevent the abdominal integument from coming in contact with ecdysteroids released from the prothoracic gland. This procedure impaired the natural increase in transcript levels in the abdominal integument. Both tweedle genes were expressed at higher levels in the empty gut than in the thoracic integument and trachea of pharate adults. In contrast, Ampxd transcripts were found in higher levels in the thoracic integument and trachea than in the gut. Together, the data strongly suggest that these three genes play roles in ecdysteroid-dependent exoskeleton construction and differentiation and also point to a possible role for the two tweedle genes in the formation of the cuticle (peritrophic membrane) that internally lines the gut.

Laccase2 is required for cuticular pigmentation in stinkbugs

During the maturation of insect cuticle, protein-protein and protein-chitin crosslinkages are formed by the action of diphenoloxidases. Two types of diphenoloxidases, laccases and tyrosinases, are present in the insect cuticle. In coleopteran and hymenopteran insects, laccase2 gene has been identified as encoding an enzyme principally responsible for cuticular pigmentation and hardening, whereas biological roles of laccase genes in hemimetabolous insects remain to be established. Here we identified laccase2 genes from three hemipteran stinkbugs, Riptortus pedestris (Alydidae), Nysius plebeius (Lygaeidae) and Megacopta punctatissima (Plataspidae). In R. pedestris, laccase2 gene was highly expressed in epidermal tissues prior to molting. When the gene expression was suppressed by an RNA interference technique, cuticular pigmentation after molting were blocked depending on the dose of injected double-stranded RNA targeting the laccase2 gene. Similar results were obtained for N. plebeius and M. punctatissima. In all the stinkbug species, injecting 20 ng of double-stranded RNA was sufficient to prevent the cuticular maturation. These results indicate that laccase2 gene is generally required for cuticular pigmentation in different stinkbug families, highlighting its conserved biological function across diverse insect taxa.

Developmental characterization, function and regulation of a Laccase2 encoding gene in the honey bee, Apis mellifera (Hymenoptera, Apinae)

In insects, exoskeleton (cuticle) formation at each molt cycle includes complex biochemical pathways wherein the laccase enzymes (EC 1.10.3.2) may have a key role. We identified an Amlac2 gene that encodes a laccase2 in the honey bee, Apis mellifera, and investigated its function in exoskeleton differentiation. The Amlac2 gene consists of nine exons resulting in an ORF of 2193 nucleotides. The deduced translation product is a 731 amino acid protein of 81.5 kDa and a pI of 6.05. Amlac2 is highly expressed in the integument of pharate adults, and the expression precedes the onset of cuticle pigmentation and the intensification of sclerotization. In accordance with the temporal sequence of exoskeleton differentiation from anterior to posterior direction, the levels of Amlac2 transcript increase earlier in the thoracic than in the abdominal integument. The gene expression lasts even after the bees emerge from brood cells and begin activities in the nest, but declines after the transition to foraging stage, suggesting that maturation of the exoskeleton is completed at this stage. Post-transcriptional knockdown of Amlac2 gene expression resulted in structural abnormalities in the exoskeleton and drastically affected adult eclosion. By setting a ligature between the thorax and abdomen of early pupae we could delay the increase in hemolymph ecdysteroid levels in the abdomen. This severely impaired the increase in Amlac2 transcript levels and also the differentiation of the abdominal exoskeleton. Taken together, these results indicate that Amlac2 expression is controlled by ecdysteroids and has a critical role in the differentiation of the adult exoskeleton of honey bees.

Insect multicopper oxidases: diversity, properties, and physiological roles

Multicopper oxidases (MCOs) are a group of related proteins that are ubiquitous in nature. They perform a wide variety of functions including pigmentation, lignin synthesis and degradation, iron homeostasis, and morphogenesis. The laccases of fungi are intensely studied for their biotechnological potential as a more environmentally friendly alternative to harsh or toxic chemicals used for certain industrial applications. Research into insect MCOs has recently attracted renewed interest as it is evident that they have diverse roles in insect physiology. MCO mRNA or enzymatic activity has been detected in extracts from epidermis, midgut, Malpighian tubules, salivary glands, and reproductive tissues. Genome sequencing has allowed for the identification of MCO genes and revealed that the number of genes can vary between species. The function of one of the genes, MCO2, has been demonstrated to be a laccase-type phenoloxidase critical for cuticle sclerotization. However, the enzymatic properties and physiological functions of the remaining MCOs remain to be elucidated. A better understanding of the roles MCOs play in insect biology may help to develop new control measures of pest species.