Cotton GhMKK1 Induces the Tolerance of Salt and Drought Stress,and Mediates Defence Responses to Pathogen Infection in Transgenic Nicotiana benthamiana

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.     

GbMPK3, a mitogen-activated protein kinase from cotton,enhances drought and oxidative stress tolerance in tobacco

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signaling modules found in all eukaryotes, and play significant roles in developmental and environmental signal transduction. In this study, a MAPK gene (GbMPK3), which showed homologous to AtMPK3 and NtWIPK, was isolated from sea-island cotton (Gossypium barbadense) and induced during multiple abiotic stress treatments including salt, cold, heat, dehydration and oxidative stress. Transgenic tobacco (Nicotiana benthamiana) with constitutively higher expression of GbMPK3 was conferred with enhanced drought tolerance, reduced water loss during drought treatment and improved plant height and survival rates after re-watering. Additionally, the gene expression levels and enzymatic activity of antioxidant enzymes were more strongly induced with depressed hydrogen peroxide accumulation in GbMPK3-overexpressing tobacco compared with wild-type under drought condition. Furthermore, observation of seed germination and leaf morphology showed that tolerance of transgenic plants to methyl viologen was improved due to increased antioxidant enzyme expression, suggesting that GbMPK3 may positively regulate drought tolerance through enhanced reactive oxygen species scavenging ability.     

The CCCH zinc finger protein gene AtZFP1 improves salt resistance in Arabidopsis thaliana

The CCCH type zinc finger proteins are a super family involved in many aspects of plant growth and development. In this study, we investigated the response of one CCCH type zinc finger protein AtZFP1 (At2g25900) to salt stress in Arabidopsis. The expression of AtZFP1 was upregulated by salt stress. Compared to transgenic strains, the germination rate, emerging rate of cotyledons and root length of wild plants were significantly lower under NaCl treatments, while the inhibitory effect was significantly severe in T-DNA insertion mutant strains. At germination stage, it was mainly osmotic stress when treated with NaCl. Relative to wild plants, overexpression strains maintained a higher K⁺, K⁺/Na⁺, chlorophyll and proline content, and lower Na⁺ and MDA content. Quantitative real-time PCR analysis revealed that the expression of stress related marker genes KIN1, RD29B and RD22 increased more significantly in transgenic strains by salt stress. Overexpression of AtZFP1 also enhanced oxidative and osmotic stress tolerance which was determined by measuring the expression of a set of antioxidant genes, osmotic stress genes and ion transport protein genes such as SOS1, AtP5CS1 and AtGSTU5. Overall, our results suggest that overexpression of AtZFP1 enhanced salt tolerance by maintaining ionic balance and limiting oxidative and osmotic stress.