Differential Chloroplast Proteomics of Temperature Adaptation in Apple (Malus x domestica Borkh.) Microshoots.

Temperature stress is one of the most common external factors that plants have to adapt to. Accordingly, plants have developed several adaptation mechanisms to deal with temperature stress. Chloroplasts are one of the organelles that are responsible for the sensing of the temperature signal and triggering a response. Here, chloroplasts are purified from low temperature (4° C), control (22° C) and high temperature (30° C) grown Malus x domestica microshoots. The purity of the chloroplast fractions is evaluated by marker proteins, as well as by using in silico subcellular localization predictions. The proteins are digested using filter-aided sample processing and analyzed using nano-LC MS/MS. 733 proteins are observed corresponding to published Malus x domestica gene models and 16 chloroplast genome -encoded proteins in the chloroplast preparates. In ANOVA, 56 proteins are found to be significantly differentially abundant (p < 0.01) between chloroplasts isolated from plants grown in different conditions. The differentially abundant proteins are involved in protein digestion, cytoskeleton structure, cellular redox state and photosynthesis, or have protective functions. Additionally, a putative chloroplastic aquaporin is observed. Data are available via ProteomeXchange with identifier PXD014212.

Endophytic Bacillus and Pseudomonas spp. Modulate Apple Shoot Growth, Cellular Redox Balance, and Protein Expression Under in Vitro Conditions.

Interactions between host plants and endophytic microorganisms play an important role in plant responses to pathogens and environmental stresses and have potential applications for plant stress management under in vitro conditions. We assessed the effect of endophytic bacteria on the growth and proliferation of domestic apple cv. Gala shoots in vitro. Further, a model apple cell suspension system was used to examine molecular events and protein expression patterns at an early stage of plant-endophyte interaction. Among the seven strains used in the study, Bacillus spp. strains Da_1, Da_4, and Da_5 and the Pseudomonas fluorescens strain Ga_1 promoted shoot growth and auxiliary shoot proliferation. In contrast, Bacillus sp. strain Oa_4, P. fluorescens strain Ga_3 and P. orientalis strain G_12 inhibited shoot development. In the cell suspension, the effects of the association between endophytic bacteria and plant cells were specific to each strain. Modulation of the cellular redox balance was monitored in the apple cells using a 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) probe, and strain-specific effects were observed that correlated with the in vitro shoot development results. Proteomic analysis revealed differences in protein expressions in apple cells co-cultivated with different Bacillus spp. strains that had contrasting effects on cellular redox balance and shoot development. The Bacillus sp. strain Da_4, which enhanced shoot development and oxidation of H2DCFDA, induced differential expression of proteins that are mainly involved in the defense response and regulation of oxidative stress. Meanwhile, treatment with Bacillus sp. strain Oa_4 led to strong upregulation of PLAT1, HSC70-1 and several other proteins involved in protein metabolism and cell development. Taken together, the results suggest that different cell signaling and response events at the early stage of the plant-endophyte interaction may be important for strain-dependent regulation of cellular redox balance and development of shoot phenotype.

Patterns of low temperature induced accumulation of dehydrins in Rosaceae crops-Evidence for post-translational modification in apple.

Important crop plants of Rosaceae family are often damaged during winter due to the lack of acclimation and cold hardiness. One of the cellular responses of plants to cold stress is the accumulation of dehydrin proteins. We studied the expression of dehydrins in several Rosaceae species during low temperature treatment in vitro. Microshoots of Pyrus communis, Malus×domestica, Fragaria vesca, Fragaria×ananassa, Prunus cerasus and Prunus avium cultivars were grown in low temperature conditions. Genotype -specific accumulation of dehydrins was detected by immunoblot analysis of the extracted proteins. Untargeted difference gel electrophoresis of Malus x domestica microshoots revealed an extensive accumulation of three dehydrins. In a protein phosphatase assay, MdDHN2 and MdDHN4, but not MdDHN6 proteins were found to be extensively phosphorylated. In terms of the amount of protein synthesized, dehydrins are a major protein-level adaptation mechanism to low temperature in M. x domestica. In addition to dehydrins, the induction of proteins involved in the response for oxidative stress were observed. Additionally, a Xero2 -like dehydrin of F. vesca was detected by difference gel electrophoresis and identified by nano LC-MS/MS.