The ethylene response factor AtERF11 that is transcriptionally modulated by the bZIP transcription factor HY5 is a crucial repressor for ethylene biosynthesis in Arabidopsis

Abstract

SUMMARYThe phytohormones abscisic acid (ABA) and ethylene are known to play multiple roles in plant development and stress responses. Ethylene biosynthesis is affected by several factors including drought, cold and the phytohormone auxin, although the role of ABA is unclear. In this work ABA-responsive mutants were screened and a bZIP transcription factor HY5 was identified as a negative regulator of ethylene biosynthesis via modulation of the expression of the ethylene biosynthesis genes ACS2 and ACS5. Members of the ethylene response factor (ERF) family of transcriptional repressors in Arabidopsis have been shown to modulate ABA responses and three ERF members were found to carry putative HY5-binding cis-acting elements. Analyses with biochemical and molecular approaches revealed that HY5 specifically binds to the G-box region of the AtERF11 promoter to activate its transcription. We further demonstrate that AtERF11, which contains a repressor motif at its C-terminal, interacts with the dehydration-responsive element in the ACS2/5 promoters, to repress its expression, resulting in decreased ethylene biosynthesis. Moreover, an AtERF11 knockout mutant showed increased levels of ACS2/5 expression and ethylene emission, while treatment with ABA greatly suppressed ACS5 transcripts but not ACS2 expression and the ethylene content, indicating that AtERF11 is a key negative regulator for ABA-mediated control of ethylene synthesis. In addition, in ethylene over-producer mutants, ABA treatment was shown to suppress ACS5 transcripts and ethylene content, thereby affecting growth and development. Based on these data, in this research we present a model suggesting that the HY5-AtERF11 regulon is a key factor modulating ABA-regulated ethylene biosynthesis.

A Regulatory Cascade Involving Class II ETHYLENE RESPONSE FACTOR Transcriptional Repressors Operates in the Progression of Leaf Senescence

“…The involvement of class II ERFs in the responses to pathogens, salt, ethylene, JA, and ABA has been reported previously (McGrath et al, 2005;Nasir et al, 2005;Song et al, 2005;Yang et al, 2005;Li et al, 2011). In particular, NbCD1, a Nicotiana benthamiana class II ERF, positively regulates cell death in the defense response of tobacco and Arabidopsis (Nasir et al, 2005).…”

The ETHYLENE RESPONSE FACTORs ERF6 and ERF11 Antagonistically Regulate Mannitol-Induced Growth Inhibition in Arabidopsis

“…ERF11 is known as a transcriptional repressor, because it possesses an EAR domain (Ohta et al, 2001;Yang et al, 2005;Nakano et al, 2006;Li et al, 2011). The simultaneous induction of a transcriptional activator and repressor suggests the presence of a regulatory network in which the repressor could attenuate the response induced by the activator.…”

“…Among the genes induced upon MBF1c overexpression (steady state), ERF6 and several ERF6 target genes, such as GA2-OX6 and WRKY33, were found, so it cannot be excluded that ERF6 also induced these genes as a secondary effect of MBF1c overexpression. Another identified candidate for transcriptional activation of ERF11 is the ELONGATED HYPOCOTYL5 (HY5), a basic leucine zipper (bZIP) transcriptional activator involved in hypocotyl growth (Lee et al, 2007;Song et al, 2008;Li et al, 2011). HY5 has been shown to bind the ERF11 promoter in vivo through its preferential CACGTG binding sequence, present in the 1-kb region upstream of the ERF11 coding sequence.…”

“…ERF11 is also known to be responsive to several hormones, especially jasmonic acid and abscisic acid (ABA), and to infection with the oomycete Phytophthora parasitica and Alternaria brassicicola (McGrath et al, 2005;Dombrecht et al, 2007;Eulgem and Somssich, 2007;Libault et al, 2007). ERF11 is further known to be a negative regulator of ethylene biosynthesis upon increased ABA levels by directly repressing the expression of the ACC synthases ACS2 and ACS5, explaining the known ABA-ethylene antagonism (Li et al, 2011). However, despite its induction by various and numerous stresses, the biological and molecular role of ERF11 in biotic and abiotic stress responses is still poorly understood.…”

“…Additionally, other small domains are conserved between several but not all ERFs, enabling a detailed classification in 12 ERF subgroups (Sakuma et al, 2002;Nakano et al, 2006). For example, the mannitol-induced ERF11 belongs to subgroup VIIIa, the members of which contain a C-terminal ERF amphiphilic repression (EAR) motif enabling transcriptional repression of the downstream targets (Ohta et al, 2001;Yang et al, 2005;Nakano et al, 2006;Li et al, 2011). The other mannitol-induced ERFs are members of the subgroups IXa (ERF1 and ERF2) or IXb (ERF5 and ERF6).…”