Abstract: 【Objective】Studying the function of mitogen activated protein kinase (MAPK) IbMPK6 in respect of low temperature stress tolerance in sweetpotato, that will help us to understand the mechanism of adaption to low temperature stress and play a fundamental role in molecular breeding of sweetpotato.【Method】Agrobacterium tumefaciens strain EHA105 harbored the plasmid 35S::IbMPK6-GFP were transformed intosweetpotato cv. Xushu29 embryogenic callus. Molecular examination and qRT-PCR were used to screen and select transgenic lines. For low temperature stress assay, selected transgenic lines were performed to observe the phenotype and determine the physiological indexes such as Fv/Fm, the content of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) after low temperature treatment and recovery treatment. Diaminobenzidine (DAB) staining and nitro blue tetrazolium (NBT) staining analysis were performed to observe reactive oxygen species (ROS) accumulation. The expression level of the key transcription factor IbCBF3 and downstream gene IbCOR27 involved in low temperature signal transduction pathway were identified before and after low temperature treatment.【Result】Twelve transgenic lines were generated and three transgenic lines (L3, L8 and L11) with a high expression level of IbMPK6 were selected for low temperature tolerance assay. Under low temperature stress, the level of Fv/Fm in transgenic lines L3, L8 and L11 was 0.79, 0.79 and 0.80, while that in WT was 0.05. After temperature recovery treatment, Fv/Fm in transgenic lines has recovered to former levels, whereas the level of Fv/Fm in WT was only 0.70, which was significantly lower than that in transgenic lines. MDA content of three transgenic (lines L3, L8 and L11) increased by 0.02 μmol·g^-1, 0.04 μmol·g^-1 and 0.02 μmol·g^-1, and it of WT increased by 0.05 μmol·g^-1 after low temperature stress treatment, respectively. After recovery treatment, MDA content in transgenic lines was 0.01 μmol·g^-1 on average, whereas it of WT was 0.03 μmol·g^-1. The results of DAB and NBT staining showed that the leaves of WT were stained deeper than those of transgenic lines, indicated that hydrogen peroxide and superoxide anion were accumulation less in transgenic lines than in WT. Furthermore, H₂O₂ level in WT was significantly higher than that in transgenic lines under low temperature stress condition and after recovery treatment. Low temperature regulated the expression level of IbCBF3 and IbCOR27 genes, but the expression level in transgenic lines was higher than that in WT.【Conclusion】Overexpression of IbMPK6 in sweetpotato resulted in enhanced tolerance to low temperature stress, via alleviating the damage of membrane and photosynthetic system, and decreasing ROS accumulation. IbMPK6 involved in low temperature signaling transduction pathway by up-regulating the expression level of cold related genes IbCBF3 and IbCOR27.

Key words: sweetpotato, IbMPK6, transgenic lines, low temperature stress