Cotton mitogen-activated protein kinase4 (GhMPK4) confers the transgenic Arabidopsis hypersensitivity to salt and osmotic stresses

Cotton (Gossypium hirsutum) as one of the most important economic crop in the world is often suffering from biotic and abiotic stresses during its growth seasons. Mitogen-activated protein kinase (MAPK) cascades participate in signal transduction of extracellular stimuli and regulate multiple biotic and abiotic stress responses in plants. In this study, a MAPK gene (GhMPK4) belonging to the group B of MAPK family was identified in cotton. Quantitative RT-PCR analysis showed that expression of GhMPK4 was induced by high salinity and osmotic stresses. Overexpression of GhMPK4 in Arabidopsis significantly enhanced the transgenic plants' sensitivity to salt and osmotic stresses and exogenous abscisic acid (ABA). Under NaCl, mannitol and ABA treatments, the rates of seed germination and cotyledon expansion/greening of the GhMPK4 overexpression transgenic lines were remarkably declined compared with those of wild type, and roots of the GhMPK4 overexpression transgenic seedlings were shorter than those of wild type. Chlorophyll and proline contents in leaves of the GhMPK4 transgenic lines were obviously lower than those in wild type. Growth status of the GhMPK4 transgenic plants was worse than that of wild type when being subjected to drought and salinity stresses. Furthermore, the expression levels of the stress-related genes were altered in the transgenic plants under NaCl, mannitol and ABA treatments, compared with those in wild type. Taken the data together, it is suggested that GhMPK4 as a negative regulator may participate in response to salt and osmotic stresses and ABA signaling through affecting the expression of the stress-related genes in plants.