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  • The promoter regions of all MdDGKs


    The promoter regions of all MdDGKs examined here included many hormone-responsive and stress-responsive elements, such as ABRE, MBS, TC-rich repeats, HSE, and LTR. Despite assumptions about how those promoters might control expression in response to environment stimuli, we found several exceptions. For example, MdDGK1 contained no MBS even though its expression was induced by drought treatment. In addition, MBSs were more numerous in MdDGK7 than in MdDGK2, even though the latter was more strongly expressed under drought treatment. Finally, expression varied among genes in response to ABA exposure even though all MdDGKs had ABREs in their promoters. Therefore, we propose that DGK gene expression is regulated by complex mechanisms based on our findings that the promoter regions of those genes contained many cis-elements that are correlated with responses to abiotic stresses and hormones.
    Conclusion In summary, the information obtained here improves our understanding of the DGK gene family in apple. Furthermore, members that responded to various stresses, based on RT-PCR results, are good candidates for further analysis of their functions and activities. This is especially true for MdDGK4 and MdDGK8, which could be used for transgenic manipulations to obtain stress-tolerant apple cultivars and rootstocks. In this research, we cloned genes from M. prunifolia and used it as materials to do expression analysis under abiotic stresses. Although we have not yet fully described the gene\'s function, our results indicate that some DGKs are active in the response and Boc-D-FMK pathway process because their transcript levels vary following exposure to drought and salt. Therefore, it may indicate that some DGK genes perhaps play critical roles in drought and salt tolerance of M. prunifolia. This will provide possibility to use these genes for rootstock breeding and improving the resistance of some rootstocks. Therefore, it will be important to further research the molecular mechanisms that control the DGK expression under drought and salt. The following are the supplementary data related to this article.
    Acknowledgments This work was supported by the National High Technology Research and Development Program of China (863 Program) (2011AA100201), and by the earmarked fund for the China Agriculture Research System (CARS-28). The authors are grateful to Priscilla Licht for help in revising our English composition.
    Introduction CD8+ T cells respond to pathogens and tumors following T cell receptor (TCR) recognition of specific peptides presented by the major histocompatibility complex (MHC). TCR-activated cells secrete interleukin 2 (IL-2), which promotes expression of CD25, the IL-2 receptor α chain that forms the high-affinity IL-2 receptor (IL2-R) together with the constitutively expressed β (CD122) and common γ chains (γc; CD132). Antigen recognition by the TCR thus ensures IL-2-dependent clonal expansion of cytotoxic T cell populations (Cantrell and Smith, 1984). Following their expansion and differentiation phase, most antigen-specific effector T cells die, and the few surviving cells develop into memory T cells. At this stage, memory cells depend largely on IL-15 (Schluns et al., 2002, Becker et al., 2002, Goldrath et al., 2002), a cytokine that shares CD122 and CD132 chains with IL-2 (Grabstein et al., 1994). CD8+ memory T cells, characterized by a CD44hiCD122hi phenotype, respond more rapidly to antigen and produce larger amounts of cytokines after antigenic challenge. In addition to conventional memory CD8+ T cells, experimental evidence has identified a preexisting pool of CD8+ T cells with a CD44hiCD122hi phenotype (Dubois et al., 2006). This population is found at high frequency in mice with impaired differentiation of conventional CD44loCD122lo CD8+ T cells, suggesting a distinct origin (Atherly et al., 2006, Broussard et al., 2006). Non-conventional CD44hiCD122hi CD8+ T cells need IL-15 to expand (Dubois et al., 2006) and are absent in IL-15−/− mice (Judge et al., 2002). They express NK (natural killer) receptors such as NKG2D, NKG2A/C/E, CD94 and Ly46, which recognize NK ligands in an MHC class I context (Dubois et al., 2006). Cytokine-mediated expansion of memory-like CD8+ T cells provides them with innate-like (non-antigen-dependent) abilities for target recognition and concurs with the capacity of IL-2 or IL-15 to generate potent CD8+ T cell-dependent anti-tumor responses (Murphy et al., 2003).