Xingqi Guo

GhMPK16, a novel stress-responsive group D MAPK gene from cotton, is involved in disease resistance and drought sensitivity

BackgroundMitogen-activated protein kinase (MAPK) cascades play pivotal roles in mediating biotic and abiotic stress responses. In plants, MAPKs are classified into four major groups (A-D) according to their sequence homology and conserved phosphorylation motifs. Members of group A and B have been extensively characterized, but little information on the group D MAPKs has been reported.ResultsIn this study, we isolated and characterised GhMPK16, the first group D MAPK gene found in cotton. Southern blot analysis suggests GhMPK16 is single copy in the cotton genome, and RNA blot analysis indicates that GhMPK16 transcripts accumulate following pathogen infection and treatment with multiple defense-related signal molecules. The analysis of the promoter region of GhMPK16 revealed a group of putative cis-acting elements related to stress responses. Subcellular localization analysis suggests that GhMPK16 acts in the nucleus. Transgenic Arabidopsis overexpressing GhMPK16 displayed significant resistance to fungi (Colletotrichum nicotianae and Alternaria alternata) and bacteria (Pseudomonas solanacearum) pathogen, and the transcripts of pathogen-related (PR) genes were more rapidly and strongly induced in the transgenic plants. Furthermore, transgenic Arabidopsis showed reduced drought tolerance and rapid H2O2 accumulation.ConclusionThese results suggest that GhMPK16 might be involved in multiple signal transduction pathways, including biotic and abiotic stress signaling pathways.

Cotton GhMPK2 is involved in multiple signaling pathways and mediates defense responses to pathogen infection and oxidative stress

Mitogen‐activated protein kinase (MAPK) cascades play important roles in mediating pathogen responses and reactive oxygen species signaling. In plants, MAPKs are classified into four major groups (A–D). Previous studies have mainly focused on groups A and B, but little is known about group C. In this study, we functionally characterized a stress‐responsive group C MAPK gene (GhMPK2) from cotton. Northern blot analysis indicated that GhMPK2 was induced not only by signaling molecules, such as ethylene and methyl jasmonate, but also by methyl viologen‐mediated oxidative stress. Transgenic tobacco (Nicotiana tabacum) plants that overexpress GhMPK2 displayed enhanced resistance to fungal and viral pathogens, and the expression of the pathogenesis‐related (PR) genes, including PR1, PR2, PR4, and PR5, was significantly increased. Interestingly, the transcription of 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) and 1‐aminocyclopropane‐1‐carboxylic acid oxidase (ACO) was significantly upregulated in transgenic plants, suggesting that GhMPK2 positively regulates ethylene synthesis. Moreover, overexpression of GhMPK2 elevated the expression of several antioxidant enzymes, conferring on transgenic plants enhanced reactive oxygen species scavenging capability and oxidative stress tolerance. These results increased our understanding of the role of the group C GhMPK2 gene in multiple defense‐signaling pathways, including those that are involved in responses to pathogen infection and oxidative stress.

Molecular cloning and characterization of a thioredoxin peroxidase gene from Apis cerana cerana.

Thioredoxin peroxidases (Tpxs) play important roles in protecting organisms against the toxicity of reactive oxygen species (ROS) and regulating intracellular signal transduction. In the present study, we cloned the full cDNA of Tpx1 encoding a 195‐amino acid protein from Apis cerana cerana (Acc). Based on the genomic DNA sequence, a 1442‐bp 5′‐flanking region was obtained, and the putative transcription factor binding sites were predicted. Quantitative PCR analysis showed that AccTpx1 was highly expressed in thorax and that the AccTpx1 transcript reached its highest level in two‐week‐old adult worker honeybees. Moreover, expression of the AccTpx1 transcript was increased by various abiotic stresses, such as ultraviolet light, HgCl2, and insecticide treatments. In addition, the recombinant AccTpx1 protein exhibited antioxidant activity; it removed hydrogen peroxide and protected DNA. These results suggest that AccTpx1 plays an important role in protecting honeybees from oxidative injury and may act in extending the lifespan of them.

The identification and oxidative stress response of a zeta class glutathione S-transferase (GSTZ1) gene from Apis cerana cerana

Glutathione-S-transferases (GSTs) play an important role in protecting organisms against the toxicity of reactive oxygen species (ROS). However, no information is available for GSTs in the Chinese honey bee (Apis cerana cerana). In this study, we isolated and characterized a zeta class GST gene (AccGSTZ1) from the Chinese honey bee. This gene is present in a single copy and harbors five exons. The deduced amino acid sequence of AccGSTZ1 shared high sequence identity with homologous proteins and contained the highly conserved features of this gene family. The temporal and spatial expression profiles of AccGSTZ1 showed that AccGSTZ1 was highly expressed in fourth instar larvae during development, and the mRNA level of AccGSTZ1 was higher in the epidermis than that in other tissues. The expression pattern under oxidative stress revealed that AccGSTZ1 transcription was significantly upregulated by external factors, such as temperature challenges and H(2)O(2) treatment. The characterization of the purified protein revealed that AccGSTZ1 had low glutathione-conjugating activity, but the recombinant AccGSTZ1 protein displayed high antioxidant activity under oxidative stress. These data suggest that AccGSTZ1 is an oxidative stress-inducible antioxidant enzyme that plays an important role in the protection against oxidative stress and may be of critical importance for the survival of the honey bees.

Identification and characterization of two phospholipid hydroperoxide glutathione peroxidase genes from Apis cerana cerana

Phospholipid hydroperoxide glutathione peroxidase (PHGPX) plays a crucial role in maintaining the integrity of membrane by reducing hydroperoxides of phospholipids. Here, we report the identification and characterization of two genes, designated AccGtpx-1 and AccGtpx-2, encoding PHGPX proteins from the Chinese honeybees, Apis cerana cerana. Alignment analysis showed that AccGtpx-1 and AccGtpx-2 shared high similarity with other known PHGPXs, which show similar structure to thioredoxin. These single copy genes showed complex exon-intron structures. The mRNA of AccGtpx-1 was detected in larvae, pupae and adults and that AccGtpx-2 was only found in adult worker bees. Furthermore, the expression of AccGtpx-1 could be induced by H(2)O(2), ultraviolet (UV) light, heat shock (37 degrees C), HgCl(2), imidacloprid, cyhalothrin, pyriproxyfen and methomyl. In contrast, AccGtpx-2 expression could only be induced by UV. These results indicated for the first time that the AccGtpx-1 and AccGtpx-2 genes encoding A. cerana cerana PHGPXs are regulated differently in response to environmental stressors.

Functional and mutational analyses of an omega-class glutathione S-transferase (GSTO2) that is required for reducing oxidative damage in Apis cerana cerana

Glutathione S‐transferases perform a variety of vital functions, particularly in reducing oxidative damage. Here, we investigated the expression patterns of Apis cerana cerana omega‐class glutathione S‐transferase 2 (AccGSTO2) under various stresses and explored its connection with antioxidant defences. We found that AccGSTO2 knockdown by RNA interference triggered increased mortality in Ap. cerana cerana, and immunohistochemistry revealed significantly decreased AccGSTO2 expression, particularly in the midgut and fat body. Further analyses indicated that AccGSTO2 knockdown resulted in decreases in catalase and glutathione reductase activities, ascorbate content and the ratio of reduced to oxidized glutathione, and increases in H2O2, malondialdehyde and carbonyl contents. We also analysed the transcripts of other antioxidant genes and found that many genes were down‐regulated in the AccGSTO2 knockdown samples, revealing that AccGSTO2 may be indispensable for attaining a normal lifespan by enhancing cellular oxidative resistance. In addition, the roles of cysteine residues in AccGSTO2 were explored using site‐directed mutagenesis. Mutants of Cys28 and Cys124 significantly affected the enzyme and antioxidant activities of AccGSTO2, which may be attributed to the changes in the spatial structures of mutants as determined by homology modelling. In summary, these observations provide novel insight into the structural and functional characteristics of GSTOs.

Characterization of the cyclin-dependent kinase 6 gene in Apis cerana cerana in response to multiple environmental stresses.

Cyclin-dependent kinases (CDKs) are serine/threonine kinases that play critical roles in the cell cycle regulation. Herein, we describe the identifi cation of a CDK gene from Apis cerana cerana, named AccCDK6. The full-length cDNA is 1,778 bp long, including an ORF of 1,380 bp that encodes a polypeptide of 459 amino acid residues. Multiple sequence alignment analysis showed that the predicted AccCDK6 sequence shares a high similarity with CDK6 genes of other species, and this protein may share an evolutionary predecessor with Drosophila CDK4. The expression patterns of the gene were also analysed, and the transcript was detected throughout the larval, pupal, and adult developmental stages. Furthermore, the expression level of the mRNA of the gene in adult workers was infl uenced by H2O2, ultraviolet (UV) light, temperature (42°C), HgCl2, and pyriproxyfen. These results indicate that AccCDK6 responds to multiple environmental stresses and may also participate in intracellular reactions of reactive oxygen species (ROS) and development processes in honey-bees