ERF Transcription Factor OsBIERF3 Positively Contributes to Immunity against Fungal and Bacterial Diseases but Negatively Regulates Cold Tolerance in Rice

We previously showed that overexpression of the rice ERF transcription factor gene OsBIERF3 in tobacco increased resistance against different pathogens. Here, we report the function of OsBIERF3 in rice immunity and abiotic stress tolerance. Expression of OsBIERF3 was induced by Xanthomonas oryzae pv. oryzae, hormones (e.g., salicylic acid, methyl jasmonate, 1-aminocyclopropane-1-carboxylic acid, and abscisic acid), and abiotic stress (e.g., drought, salt and cold stress). OsBIERF3 has transcriptional activation activity that depends on its C-terminal region. The OsBIERF3-overexpressing (OsBIERF3-OE) plants exhibited increased resistance while OsBIERF3-suppressed (OsBIERF3-Ri) plants displayed decreased resistance to Magnaporthe oryzae and X. oryzae pv. oryzae. A set of genes including those for PRs and MAPK kinases were up-regulated in OsBIERF3-OE plants. Cell wall biosynthetic enzyme genes were up-regulated in OsBIERF3-OE plants but down-regulated in OsBIERF3-Ri plants; accordingly, cell walls became thicker in OsBIERF3-OE plants but thinner in OsBIERF3-Ri plants than WT plants. The OsBIERF3-OE plants attenuated while OsBIERF3-Ri plants enhanced cold tolerance, accompanied by altered expression of cold-responsive genes and proline accumulation. Exogenous abscisic acid and 1-aminocyclopropane-1-carboxylic acid, a precursor of ethylene biosynthesis, restored the attenuated cold tolerance in OsBIERF3-OE plants while exogenous AgNO3, an inhibitor of ethylene action, significantly suppressed the enhanced cold tolerance in OsBIERF3-Ri plants. These data demonstrate that OsBIERF3 positively contributes to immunity against M. oryzae and X. oryzae pv. oryzae but negatively regulates cold stress tolerance in rice.

The Transcription Factor HcERF4 Confers Salt and Drought Tolerance in Kenaf (Hibiscus Cannabinus L.)

Ethylene response factors (ERF) are members of the APETALA2/ERF transcription factor family, and they play an important role in plant growth, development, and response to various environmental stresses. In the present study, an ERF transcription factor HcERF4 was isolated and characterized from kenaf. The protein encoded by the HcERF4 has 233 amino acid residues with a theoretical isoelectric point of 8.89 and a predicted molecular weight of 25.53 kDa. HcERF4 had an over than 86.97% identity to HsERF4(XP_039019980.1), and shared a closest phylogenetic relationship with Hibiscus syriacus. Subcellular localization analysis shows that HcERF4 is located in the nucleus. Transactivation assays in yeast demonstrated that HcERF4 functions as a transcriptional activator. The expression of HcERF4 was enriched in leaf and root, and can be induced by salt or drought treatments in kenaf. The VIGS-silenced HcERF4 plant showed significantly reduced plant height, stem diameter, fresh weight, and relative water content (RWC) compared with wild type plants under salt or drought stress condition; In addition, the contents of MDA, O2−, H2O2, and free proline is significantly increased, and the activities of SOD and CAT are significantly reduced. The DAB/NBT staining results showed that the H2O2 and O2− contents in HcERF4-silenced plants were consistent with the determination. Based on these results, it is proposed that HcERF4 plays an important role in regulating salt and drought stress in kenaf.

Ethylene-Inducible AP2/ERF Transcription Factor Promotes Capsaicinoid Biosynthesis in Capsicum

Ethylene is very important in the process of plant development and regulates the biosynthesis of a lot of secondary metabolites. In these regulatory mechanisms, transcription factors that mediate ethylene signals play a very important role. Capsaicinoids (CAPs) only synthesized and accumulated in Capsicum species, causing their fruit to have a special pungent taste, which can protect against attack from herbivores and pathogens. In this study, we identified the transcription factor CcERF2, which is induced by ethylene, and demonstrated its regulatory effect on CAPs biosynthesis. Transcriptome sequencing analysis revealed the expression patterns of CcERF2 and multiple genes associated to CAPs biosynthesis were basically the same. The spatiotemporal expression results showed CcERF2 was preferentially expressed in the placenta of the spicy fruit. Ethylene can induce the expression of CcERF2 and CAPs biosynthesis genes (CBGs). CcERF2 gene silenced, 1-MCP and PZA treatments caused a decrease in expression of CBGs and a sharp decrease in content of CAPs. The results indicated CcERF2 was associated with the CAPs biosynthesis.

An apple (Malus domestica) AP2/ERF transcription factor modulates carotenoid accumulation

Color is an important trait for horticultural crops. Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health. Here, we identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) transcription factor named MdAP2-34 in apple (Malus domestica Borkh.). MdAP2-34 expression exhibited a close correlation with carotenoid content in ‘Benin Shogun’ and ‘Yanfu 3’ fruit flesh. MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway. The major carotenoid contents of phytoene and β-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin, yet the predominant compound of lutein showed no obvious difference, indicating that MdAP2-34 regulates phytoene and β-carotene accumulation but not lutein. MdPSY2-1 (phytoene synthase 2) is a major gene in the carotenoid biosynthesis pathway in apple fruit, and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34. In addition, overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents. Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple, and this research is valuable for accelerating the apple breeding process.

Genome-Wide Identification and Characterization of AP2/ERF Transcription Factor Family Genes in Oil Palm under Abiotic Stress Conditions

The AP2/ERF transcription factor family members play crucial roles in controlling plant growth and development, as well as responses to various abiotic stresses. Genome-wide identification and characterization of AP2/ERF genes has not yet been carried out in the oil palm genome. In the present work, we reported the occurrence of 172 EgAP2/ERFs (AP2, ERF, RAV & Soloist members) through genome-wide identification. Phylogenetic analysis was used to divide them into four groups, including: 34 AP2, 131 ERF, 5 RAV, and 2 Soloist gene family members. All 172 AP2/ERF members were unevenly distributed across 16 chromosomes of oil palm. Gene duplication analysis elucidated the tandem duplication of AP2/ERFs on chromosome blocks of the oil palm genome during evolution. Gene structure as well as conserved motif analysis demonstrated the conserved nature of intron/exon organization and motifs among the AP2/ERF genes. Several cis-regulatory elements—related to hormone, stress, and defense responses—were identified in the promoter regions of AP2/ERFs. Tissue-specific expression of 172 AP2/ERFs in five different tissues of oil palm was also revealed by heatmap analysis using the available transcriptome data. Finally, abiotic stress (salinity, cold & drought)-responsive AP2/ERFs in the oil palm genome were validated through qPCR analysis. Our study provided valuable information on oil palm AP2/ERF superfamily members and dissected their role in abiotic stress conditions.

Intrinsic Disorder in Plant Transcription Factor Systems: Functional Implications

Eukaryotic cells are complex biological systems that depend on highly connected molecular interaction networks with intrinsically disordered proteins as essential components. Through specific examples, we relate the conformational ensemble nature of intrinsic disorder (ID) in transcription factors to functions in plants. Transcription factors contain large regulatory ID-regions with numerous orphan sequence motifs, representing potential important interaction sites. ID-regions may affect DNA-binding through electrostatic interactions or allosterically as for the bZIP transcription factors, in which the DNA-binding domains also populate ensembles of dynamic transient structures. The flexibility of ID is well-suited for interaction networks requiring efficient molecular adjustments. For example, Radical Induced Cell Death1 depends on ID in transcription factors for its numerous, structurally heterogeneous interactions, and the JAZ:MYC:MED15 regulatory unit depends on protein dynamics, including binding-associated unfolding, for regulation of jasmonate-signaling. Flexibility makes ID-regions excellent targets of posttranslational modifications. For example, the extent of phosphorylation of the NAC transcription factor SOG1 regulates target gene expression and the DNA-damage response, and phosphorylation of the AP2/ERF transcription factor DREB2A acts as a switch enabling heat-regulated degradation. ID-related phase separation is emerging as being important to transcriptional regulation with condensates functioning in storage and inactivation of transcription factors. The applicative potential of ID-regions is apparent, as removal of an ID-region of the AP2/ERF transcription factor WRI1 affects its stability and consequently oil biosynthesis. The highlighted examples show that ID plays essential functional roles in plant biology and has a promising potential in engineering.