Abstract
Nuclear factor Y (NF-Y) family proteins are involved in many developmental processes and responses to environmental cues in plants, but whether and how they regulate phytohormone abscisic acid (ABA) signaling need further studies. In the present study, we showed that over-expression of the NF-YC9 gene confers ABA hypersensitivity in both the early seedling growth and stomatal response, while down-regulation of NF-YC9 does not affect ABA response in these processes. We also showed that over-expression of the NF-YC9 gene confers salt and osmotic hypersensitivity in early seedling growth, which is likely to be directly associated with the ABA hypersensitivity. Further, we observed that NF-YC9 physically interacts with the ABA-responsive bZIP transcription factor ABA-INSENSITIVE5 (ABI5), and facilitates the function of ABI5 to bind and activate the promoter of a target gene EM6. Additionally, NF-YC9 up-regulates expression of the ABI5 gene in response to ABA. These findings show that NF-YC9 may be involved in ABA signaling as a positive regulator and likely functions redundantly together with other NF-YC members, and support the model that the NF-YC9 mediates ABA signaling via targeting to and aiding the ABA-responsive transcription factors such as ABI5.
Highlights
The phytohormone abscisic acid (ABA) regulates plant growth, development, and responses to a variety of abiotic stress (Finkelstein et al 2002; Adie et al 2007; Cutler et al 2010)
In the absence of exogenously applied ABA, there was no significant difference found between the wild-type and NF-YC9-overexpressing lines (OE1 and OE6) plants in the early seedling growth, while the early seedling growth of the OE1 and OE6 lines was significantly more reduced than that of the wildtype seedlings in the ABA-containing medium (Fig. 1c–f)
We found that the knockdown mutants nf-yc9-1and nf-yc9-2 displayed wild-type phenotypes in early seedling growth and stomatal response (Figs. 1, 2), suggesting that the Arabidopsis NF-YC family proteins may function redundantly in these ABA-mediated processes
Summary
The phytohormone abscisic acid (ABA) regulates plant growth, development, and responses to a variety of abiotic stress (Finkelstein et al 2002; Adie et al 2007; Cutler et al 2010). Numerous regulators of ABA signaling, including receptors for ABA, have been identified, revealing the functional mechanism of this phytohormone from signal perception to downstream gene expression (for review, see Cutler et al 2010). Each of the three subunits has multiple members (Stephenson et al 2007; Siefers et al 2009; Laloum et al 2013). The NF-YA, NF-YB and NF-YC subunits usually form a huge number of heterotrimer complex, which functions to bind DNA and regulate gene expression (Gusmaroli et al 2001; Petroni et al 2012). It has been believed that, while the NF-Y proteins have retained high degrees of similarity, especially in the residues necessary for NF-Y complex formation and DNA
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