Proteomics-based Investigation On Cold Tolerance Mechanism Of Rhododendron Chrysanthum Pall.

Rhododendron chrysanthum Pall.(R.chrysanthum),belonging to the family of Ericaceae,has significant ornamental and medicinal values.R.chrysanthum only grows at altitudes between 1,300 m and 2,506 m on the Changbai Mountain where belongs to alpine tundra.In the long-term adaptive evolution,R.chrysanthum has evolved sophisticated cold resistance mechanisms and can serve as a significant plant resource for investigating cold tolerance in alpine plants.Low temperature seriously affects the distribution and production of plants.Therefore,further investigation on the physiological and molecular mechanisms underlying cold tolerance is significant to improve the cold tolerance of crops and the breeding of cold-tolerant varieties.In our study,wild type(cold-tolerant)and domesticated(cold-sensitive)R.chrysanthum were used as the experimental(EG)and control groups(CG),respectively.All plant materials were exposed to 4°C for 12 h.Then proteomic analysis,combined with physiological and biochemical analyses,including the western blotting for rubisco large subunit(RbcL),the measurement of chlorophyll fluorescence,and the assay of antioxidant enzyme activities,was performed.A total of 705 proteins were quantified,among which 137 proteins were up-regulated(UR)in the EG.Subcellular localization analysis showed that 42% of the UR proteins were localized in chloroplast.This indicated that the metabolic processes localized in chloroplast are sensitive to low temperature and play important roles in the process of response to cold stress.The results of western blot,protein interaction network analyses,and chlorophyll fluorescence measurement,suggested that the photosynthesis capacity and the photochemical activity of the EG are much higher than the CG under the cold stress.These results also revealed that the EG can reduce the cold-induced injury by adjusting the distribution of light and activating the defense mechanisms.The activities of superoxide dismutase(SOD),catalase(CAT),ascorbate peroxidases(APXs),and glutathione peroxidase(GPX)were significantly higher and the expression of APXs and GPX were also increased in the EG.Furthermore,in the interaction network most of the proteins were localized in chloroplast,suggesting that complex connections exist between the photosynthetic process and redox adjustment,and the antioxidant system plays a vital role in response to low temperature stress and the cold tolerance of plants.This is the first report that the proteomic approach was used to investigate the molecular mechanism of cold stress tolerance,and the dynamic changes in proteome of R.chrysanthum.Comparative proteomic analysis,combined with bioinformatic,physiological and biochemical analyses,was performed to reveal the roles of light utilization and antioxidant system in the cold tolerance of plants in both protein and molecular level.These data provide valuable information about the molecular mechanism involved in the cold tolerance of R.chrysanthum and have a higher reference value for further investigation.