Multiple regulatory roles of AP2/ERF transcription factor in angiosperm

Abstract

APETALA2/ethylene response factor (AP2/ERF) transcription factor (TF) is a superfamily in plant kingdom, which has been reported to be involved in regulation of plant growth and development, fruit ripening, defense response, and metabolism. As the final response gene in ethylene signaling pathway, AP2/ERF TF could feedback modulate phytohormone biosynthesis, including ethylene, cytokinin, gibberellin, and abscisic acid. Moreover, AP2/ERF TF also participates in response to the signals of auxin, cytokinin, abscisic acid, and jasmonate. Thus, this superfamily is key regulator for connecting the phytohormonal signals. In this review, based on the evidence of structural and functional studies, we discussed the multiple regulator roles of AP2/ERF TF in angiosperm, and then constructed the network model of AP2/ERF TF in response to various phytohormonal signals and regulatory mechanism of the cross-talk.

Keywords: AP2/ERF TF; Fruit ripening; Phytohormones; Plant growth and development; Stress.

Fig. 1

A network model for AP2/ERF genes response to phytohormones and regulating downstream effectors in angiosperm. Ethylene biosynthesis pathway, ethylene signaling pathway, and ripening regulators are indicated by yellow, green, and gray colors, respectively. AP2/ERF family members is boxed and filled with red color. In ethylene biosynthesis pathway, S-adenosine methionine (SAM) is converted to ethylene (ET) via an intermediate metabolites 1-aminocyclopropane-1-carboxyla (ACC), underlying the catalysis of the two enzymes 1-aminocyclopropane-1-carboxyla synthase (ACS) and oxidase (ACO). In ethylene signaling pathway, ET is firstly combined with ethylene receptor (ETR) to activate constitutive triple response (CTR), leading to expression of ethylene insensitive (EIN) and EIN-induced ethylene insensitive-like (EIL). EIL promote expression of ethylene response factor (ERF), including activator and repressor. The ERF activities are induced by auxin (IAA), cytokinin (CTK), abscisic acid (ABA), and jasmonate (JA), as well as ripening-related genes, such as RIPENING INHIBITOR (RIN), NON-RIPENING (NOR), COLORLESS NON-RIPENING (CNR), and Homeodomain-leucine zipper HOMEOBOX (HB-1). Meanwhile, ERF can reduce CTK and gibberellin (GA) levels but increase ABA biosynthesis. In ethylene responses, ERF also regulate ethylene level by enhancing and decreasing ACS/ACO activity mediated by the activators and repressors, respectively. As for effectors of plant growth, defense responses and fruit ripening, ERF can directly medium the expression by binding to GCC-box/DREB element in the promoter, and have the ability to indirectly regulate it, due to few ERFs inhibit expression of RIN, NOR, CNR, and HB-1 that can directly bind to the promoter of effectors