Function Analyses Of GhMPK6a And GhMPK20from Cotton

During the evolution of plants, Mitogen-activated protein kinase (MAPK) pathway playsa pivotal role in sensing and transmitting the signals from a changing environment intointracellular. The adaptive/defensive physiological and biochemical responses are followed bysignal transduction. So far, MAPK cascades carry out signal transduction in response toabiotic and biotic stress, such as drought, salinity and pathogens infection. However, moststudies are focused on model plants such as Arabidopsis and tobacco; studies of MAPKs incrops are limited. Moreover, the functions of MAPKs under different genetic backgroundsperhaps differ from each other. Thus, the functions of MAPKs in crops, especially theirmolecular mechanisms under different genetic backgrounds, still require further investigation.Cotton (Gossypium hirsutum) is the important fibre-and oil-producing crop in the world. Inthis study, two multiple stress-responsive cotton MAPK genes, namely GhMPK6a andGhMPK20, were identified and characterized. The main results are as follows:(1) Two multiple stress-responsive cotton MAPK genes, namely GhMPK6a andGhMPK20, were identified by homology cloning. GhMPK6a is a group A MAPK, whileGhMPK20is a group D MAPK. Subcellular localization indicated that both of these twogenes were localized in both the cytoplasm and the nucleus. Thus, they may function in boththe cytoplasm and the nucleus.(2) The expression patterns of GhMPK6a and GhMPK20indicate that they could beinduced by various abiotic stimuli, such as salt, wounding, drought, low temperature; diversesignalling molecules, such as abscissic acid (ABA), ethylene (ET), jasmonate (JA); and bioticstimuli such as the bacterial pathogen Ralstonia Solanacearum. These results indicate thatGhMPK6a and GhMPK20may be involved in responses to multiple abiotic and bioticstresses.(3) Ectopic expression of GhMPK6a and GhMPK20in Nicotiana benthamiana reduced drought and salt tolerance. Moreover, plants overexpressing GhMPK6a were sensitive to thebacterial pathogen R. solanacearum. Histochemical analysis of β-glucuronidase (GUS)activity revealed that GhMPK6a exhibits tissue-specific expression during post-germinationdevelopment, mixed bud differentiation and pollination. The promoter analysis by theprograms PlantCARE and PLACE indicate that GhMPK20maybe function in developmentprocesses.(4) GhMPK6a and GhMPK20can interact with upstream MAPKK GhMKK4asevidenced by yeast two-hybrid system and bimolecular fluorescence complementation (BiFC)system, redeeming the deficiency on MAPK interaction partners in cotton crop.