Functional Phosphoproteomic Analysis Reveals That a Serine-62-Phosphorylated Isoform of Ethylene Response Factor110 Is Involved in Arabidopsis Bolting

Ethylene is a major plant hormone that plays an important role in regulating bolting, although the underlying molecular mechanism is not well understood. In this study, we report the novel finding that the serine-62 (Ser-62) phosphorylation of Ethylene Response Factor110 (ERF110) is involved in the regulation of bolting time. The gene expression and posttranslational modification (phosphorylation) of ERF110 were analyzed among ethylene-response mutants and ERF110 RNA-interfering knockout lines of Arabidopsis (Arabidopsis thaliana). Physiological and biochemical studies revealed that the Ser-62 phosphorylation of ERF110 was closely related to bolting time, that is, the ethylene-enhanced gene expression of ERF110 and the decreased Ser-62 phosphorylation of the ERF110 protein in Arabidopsis. The expression of a flowering homeotic APETALA1 gene was up-regulated by the Ser-62-phosphorylated isoform of the ERF110 transcription factor, which was necessary but not sufficient for normal bolting. The gene expression and phosphorylation of ERF110 were regulated by ethylene via both Ethylene-Insensitive2-dependent and -independent pathways, which constitute a dual-and-opposing mechanism of action for ethylene in the regulation of Arabidopsis bolting.