Mitogen-activated protein kinase kinases (MAPKK) mediate a variety of stress responses in plants. So far little is known on the functional role of MAPKKs in cotton. In the present study, Gossypium hirsutum MKK1 (GhMKK1) function was investigated. GhMKK1 protein may activate its specific targets in both the nucleus and cytoplasm. Treatments with salt, drought, and H2O2 induced the expression of GhMKK1 and increased the activity of GhMKK1, while overexpression of GhMKK1 in Nicotiana benthamiana enhanced its tolerance to salt and drought stresses as determined by many physiological data. Additionally, GhMKK1 activity was found to up-regulate pathogen-associated biotic stress, and overexpression of GhMKK1 increased the susceptibility of the transgenic plants to the pathogen Ralstonia solanacearum by reducing the expression of PR genes. Moreover, GhMKK1-overexpressing plants also exhibited an enhanced reactive oxygen species scavenging capability and markedly elevated activities of several antioxidant enzymes. These results indicate that GhMKK1 is involved in plants defence responses and provide new data to further analyze the function of plant MAPK pathways.

Oxidative stress may be the most significant threat to the survival of living organisms. Glutathione S-transferases (GSTs) serve as the primary defences against xenobiotic and peroxidative-induced oxidative damage. In contrast to other well-defined GST classes, the Omega-class members are poorly understood, particularly in insects. Here, we isolated and characterised the GSTO2 gene from Apis cerana cerana (AccGSTO2). The predicted transcription factor binding sites in the AccGSTO2 promoter suggested possible functions in early development and antioxidant defence. Real-time quantitative PCR (qPCR) and western blot analyses indicated that AccGSTO2 was highly expressed in larvae and was predominantly localised to the brain tissue in adults. Moreover, AccGSTO2 transcription was induced by various abiotic stresses. The purified recombinant AccGSTO2 exhibited glutathione-dependent dehydroascorbate reductase and peroxidase activities. Furthermore, it could prevent DNA damage. In addition, Escherichia coli overexpressing AccGSTO2 displayed resistance to long-term oxidative stress exposure in disc diffusion assays. Taken together, these results suggest that AccGSTO2 plays a protective role in counteracting oxidative stress.

Extracellular signal-regulated kinase (ERK), a mitogen-activated protein kinase (MAPK), plays roles in a variety of cellular responses. However, limited information is available on the relationship between ERKs and environmental stresses. In this report, an ERK gene, AccERK2, was cloned and characterized from Apis cerana cerana. Polypeptide sequence alignment revealed that the single-copied AccERK2 shares high identity with other known ERKs and contains the typical conserved Thr-Glu-Tyr (TEY) motif in its activation loop. Genomic sequence analysis revealed that the seven exons of AccERK2 are interrupted by six introns, and the seventh intron is located in the 3' untranslated region. Semi-quantitative reverse transcription (RT-PCR) indicated that AccERK2 was expressed at higher levels in the larval and pupal stages than in the adult stage. AccERK2 was also most highly expressed in the brain. The expression of AccERK2 was induced by abiotic stresses, including heat, ion irradiation, oxidative stress, and heavy metal ions. Based on these results, it appears that AccERK2 in A. cerana cerana participates in developmental processes, the nervous system, and responses to environmental stressors.