Phosphoproteomics-identified ERF110 affects ... - Plant Physiology

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EIL1, is regulated both by F-box proteins and ethylene-regulated Ubiquitin/26S
proteasome-dependent protein degradation systems (Zhao and Guo, 2011).
In combination with the intricate transcriptional regulatory networks, protein
phosphorylation has also been reported to be involved in ethylene signaling events
(Raz and Fluhr, 1993; Li et al., 2009; Stepanova and Alonso, 2009). Receptors and
many of the key regulatory components in ethylene signaling have kinase activities
(Gamble et al., 2002; Gao et al., 2003; Wang et al., 2003; Kendrick and Chang, 2008).
Although the negative regulator of the ethylene response –– CTR1, which is a
putative mitogen-activated protein kinase kinase kinase (MAPKKK) –– directly
phosphorylates and inactivates EIN2 in the air, the role of other MAPKs in ethylene
signaling is still controversial (Ju et al., 2012). MAPK cascades have been reported to
be involved in the regulation of ethylene signaling and ethylene-regulated
phosphorylation of EIN3 (Ouaked et al., 2003; Yoo et al., 2008) and especially in the
control of ethylene biosynthesis (Liu and Zhang, 2004). The phosphorylation of EIN3
protein appears to play a dual role in the regulation of its stability, which suggests a
direct link between the protein phosphorylation regulatory network and the regulatory
mechanism of transcription factors in ethylene signaling. Thus, it is speculated that
the dual-and-opposing effect of ethylene on flowering is mediated by both
transcriptional and post-translational levels in Arabidopsis.
To address the complex yet interesting phenomenon via an unbiased approach,
label-free quantitative phosphoproteomics was performed on ethylene-regulated
protein phosphorylation, identifying ERF110 as one of the putative novel ethylene
signaling components (Li et al., 2009). This ERF110 gene encodes a transcriptional
factor that belongs to the B4 subfamily of the ERF protein family (Nakano et al.,
2006), which was predicted to be phosphorylated or/and de-phosphorylated in an
EIN2-independent manner. The ERF gene family displays diverse cellular functions,
ranging from plant responses to biotic or abiotic stress to hormone treatment
(Ohmetakagi and Shinshi, 1995; Nakano et al., 2006).
We report here the ethylene-regulated phosphorylation of ERF110, the
ethylene-regulated Ser62-phosphorylated isoform of which was found to be required
for normal Arabidopsis bolting. Subsequently, a downstream flowering homeotic gene
AP1 was up-regulated by Ser62-phosphorylated ERF110 at the transcriptional level,