Abstract
BackgroundMost studies on the paper mulberry are mainly focused on the medicated and pharmacology, fiber quality, leaves feed development, little is known about its mechanism of adaptability to abiotic stress. Physiological measurement, transcriptomics and proteomic analysis were employed to understand its response to cold stress in this study.MethodsThe second to fourth fully expanded leaves from up to down were harvested at different stress time points forthe transmission electron microscope (TEM) observation. Physiological characteristics measurement included the relative electrolyte leakage (REL), SOD activity assay, soluble sugar content, and Chlorophyll fluorescence parameter measurement. For screening of differentially expressed genes, the expression level of every transcript in each sample was calculated by quantifying the number of Illumina reads. To identify the differentially expressed protein, leaves of plants under 0, 6, 12, 24, 48 and 72 h cold stress wereharvested for proteomic analysis. Finally, real time PCR was used to verify the DEG results of the RNA-seq and the proteomics data.ResultsResults showed that at the beginning of cold stress, respiratory metabolism was decreased and the transportation and hydrolysis of photosynthetic products was inhibited, leading to an accumulation of starch in the chloroplasts. Total of 5800 unigenes and 38 proteins were affected, including the repressed expression of photosynthesis and the enhanced expression in signal transduction, stress defense pathway as well as secondary metabolism. Although the transcriptional level of a large number of genes has been restored after 12 h, sustained cold stress brought more serious injury to the leaf cells, including the sharp rise of the relative electrolyte leakage, the declined Fv/Fm value, swelled chloroplast and the disintegrated membrane system.ConclusionThe starch accumulation and the photoinhibition might be the main adaptive mechanism of the paper mulberry responded to cold stress. Most of important, enhancing the transport and hydrolysis of photosynthetic products could be the potential targets for improving the cold tolerance of the paper mulberry.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2047-6) contains supplementary material, which is available to authorized users.
Highlights
Most studies on the paper mulberry are mainly focused on the medicated and pharmacology, fiber quality, leaves feed development, little is known about its mechanism of adaptability to abiotic stress
To obtain the ultrastructure changes of the paper mulberry leaf during cold stress, the treated leaves were made into ultrathin slices for transmission electron microscope (TEM) observation
The cell membrane showed no obvious change before 12 h (Fig. 1a–c)
Summary
Most studies on the paper mulberry are mainly focused on the medicated and pharmacology, fiber quality, leaves feed development, little is known about its mechanism of adaptability to abiotic stress. The paper mulberry belongs to the family of Moraceae and is naturally distributed in Eastern Asia and pacific countries [1], which has shallow roots with advanced lateral roots and without an obvious taproot. Because of its fast growth and adaptability, the paper mulberry is commonly used for the ecological afforestation and. Many research have been carried out on paper making and medicine, while there are relatively few studies on physiological and molecular mechanisms responded to abiotic stress. BpDREB2, cloned from the paper mulberry, can significantly enhance the freezing tolerance of Arabidopsis without causing growth retardation [13]. The molecular mechanism about cold stress tolerance of the paper mulberry has not been studied, which limits its exploitation
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