In general, the AP2/ERF TFs in response to abiotic stresses are the members of DREB family (Licausi et al. Most studies have found the importance of AP2/ERF TF in defense of various stresses. Both abiotic and biotic stresses are mediated by multiple transcriptional factors, such as NAC, WRKY, MYB, bHLH, bZIP, and ERF (Abe et al. Stresses are the negative environment factors around plant growth and development. Thus, AP2/ERF TF is not only in response to ethylene signal transduction, but also can feedback regulate ethylene synthesis in plant tissues. Noteworthy, this subset contains the aforementioned activators and repressors of ethylene biosynthesis and signal pathway genes. In addition, ERF.B3 has the ability to modulate the transcription levels of a subset of other ERF TFs (Liu et al. Besides the positive feedback genes, few ERF TFs also represent as repressor of ACS and ACO activities to prevent ethylene biosynthesis, including AtERF4, AtERF11, SlERF6, and MaERF11 (Lee et al. However, due to GCC-box usually presented in the promoter of ACS and ACO in many plants, the expressed ERF genes will enhance the activities of the two genes, thereby accelerate ethylene biosynthesis and signal transduction, such as LeERF1, AtERF73/HRE1, TERF2/LeERF2, and MaERF9 (Li et al. The EIN/EIL proteins bind to upstream regions of ERF TFs to promote it expressed in tissues (Alexander and Grierson 2002 Guo and Ecker 2003 Solano et al. The produced ethylene in plant tissues is combined with ETR (Ethylene receptor) to activate constitutive triple response (CTR), and then induce expression of a set of ethylene insensitive (EIN) and Ethylene insensitive-like (EIL). Sequentially, how much ethylene produced in plant tissues are positive correlated to ACS and ACO activities. Ethylene is synthesized by ACS (1-aminocyclopropane-1- carboxyla synthase) catalyzing substrate of SAM (S-adenosyl methionine) to form ACC (1-aminocyclopropane-1-carboxyla acid), and then impel by ACO (1-aminocyclopropane-1-carboxyla oxidase). 2003).Įthylene is an important phytohorome for plant growth, development, senescence, and stress tolerance. In addition, few reports reveal that ERF proteins could interact directly with a non-GCC element containing promoters (Chakravarthy et al. Moreover, ERF protein can also bind to VWRE (vascular wounding responsive element, GAAAAGAAAATTTC) and CE1 (coupling element, CACCG) in tobacco (Sasaki et al. Besides GCC-box and DRE/CRT, the elements diverged from these two also belong to cis-regulatory elements, which may be in response to different stimuli underlying various stresses (Mizoi et al. For instance, the members are weak activators in group A, B and E, neutral in class G and H, and strong in group C, whereas that are as repressor in group F (Pirrello et al. Noteworthy, most AP2/ERF proteins can bind GCC-box containing promoter, but the activation degree is different among members in various groups. Of these cis-regulatory elements, GCC-box (AGCCGCC element) and DRE/CRT (dehydrationresponsive element/C-repeat, RCCGCC element) are the mainly two DNA-binding elements (De Boer et al. 2008).ĪP2/ERF proteins have strongly capacity to bind a wide range of cis-regulatory elements in promoter of target genes (Sasaki et al. 2012), whereas the traditionally classification is used in other plant species, including Salix arbutifolia, Nicotiana tabacum, and Populus trichocarpa (Rao et al. The re-designated classification is employed in horticultural plants, such as Vitis vinifera, Prunus mume, and Solanum lycopersicon (Licausi et al. However, these twelve groups are re-designated with group I to X, VI-L, and Xb-L or group A to J (Nakano et al. Of the DREB and ERF families, all the members are further classified into six groups, A1 to A6 and B1 to B6, respectively (Sakuma et al. 2002), resulting in a novel DREB family is separated from ERF family (Du et al. Because of ERF family members could bind to two mainly DNA-binding elements (Hao et al. Soloist family have little members (one or two) that also contain a single AP2 domain in all sequenced plant genome, but they strongly diverged in gene sequence from other AP2/ERF members (Du et al. RAV members comprise by a consensus sequence elements for both AP2 domain and B3 domains (Kagaya et al. ERF members characterize by a single AP2 domain (Nakano et al. AP2 members constitute by one or additionally taking a tandem repeated AP2 domain (Kagaya et al. Based on the difference of this domain in copy numbers, AP2/ERF TF could usually be divided into four families, AP2, ERF, RAV, and Soloist (Nakano et al. According to previous reports, the superfamily AP2/ERF members contain a common DNA binding domain, AP2 domain.

Srdx transcription