CaMKK1 from Chenopodium album positively regulates salt and drought tolerance in transgenic tobacco

Plants encounter various abiotic stresses during the whole life cycle. The mitogen-activated protein kinase kinase (MAPKK) acts as the convergent point of MAPK cascade in stress signaling pathway, which has not widely been studied so far. In the present study, we isolated a group A MAPKK gene (named as CaMKK1 ) from Chenopodium album , a salt-tolerant plant species in Chenopodiaceae. Quantitative RT-PCR analysis indicates that CaMKK1 was significantly up-regulated and displayed a fast and transient activation, which was similar with MAPK expression pattern in C. album under salt and drought stress. Ectopic expression of CaMKK1 in Escherichia coli BL21 (DE3) strains showed that overexpression of CaMKK1 could increase the salt and drought tolerance to bacterium. Overexpression of CaMKK1 in transgenic tobacco exhibited attenuated salt and PEG sensitivity by means of improving germination percentage and seedling growth. Furthermore, transgenic tobacco lines significantly accumulated organic osmoprotectants, and increased antioxidant enzyme activities which effectively relieved the accumulated reactive oxygen species under stress; the water loss rate was reduced and net photosynthetic rate was significantly increased in transgenic lines compared to non-transgenic plant. The more worth mentioning is that the transcripts of downstream transcription factors ( NtDREB2, NtDREB3, NtDREB4 ) were quickly and dramatically accumulated (from 15 to 224 folds) in transgenic lines under stress. In conclusion, our results indicate that CaMKK1 is a positive regulator in response to salt and drought stress in plants, which should provide new data for further analyzing the function of plant MAPK pathway.