PLANT DEFENSE: ROLE OF TRANSCRIPTION FACTOR

Plant transcription factors (TFs) are sequence-specific DNA-binding proteins that play role in defense responses against pathogen attack. Transcription factor has four domain (Liu et al., 1999), a DNA binding domain, an oligomerization site, a transcription-regulation domain and a nuclear localization signal (NLS). The DNA- binding domain is responsible for binding of the TFs to specific cis-regulatory DNA sequences in the promoters of genes that they regulate. The NLS are short peptide motifs that mediate the nuclear import of protein by binding to their receptor known as importins (Kosugi et al., 2009). Some plant TFs may lack NLS but can be imported in the nucleus by dimerizing with proteins that possess these signals. The DNA-binding basic domain of helix-loop-helix TFs may serve as NLS (Goldfarb and Lewandowska 1994).  

There are two mechanism of transmission of signals from cell-surface receptors to the nucleus and both involve protein phosphorylation (Karin and Hunter 1995):

  1. First: A regulated translocation of activated protein kinases from the cytoplasm into the nucleus where they phosphorylate target transcription factors
  2. Second: The TFs are inactive in the cytoplasm but upon activation are translocated into the nucleus.

Upon  receiving a signal from the cell membrane signal transduction, TFs are activated and then translocated from the cytoplasm into the nucleus where they interact with the corresponding DNA frame (cis-acting elements) (Liu et al., 2018). Phosphorylation has the ability to modulate nuclear translocation.

Transcription Factor families are as follows:

  1. WRKY
  2. APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF)
  3. BASIC-DOMAIN LEUCINE-ZIPPER (bZIP)
  4. BASIC HELIX-LOOP-HELIX (bHLH)
  5. NAM/ATAF/CUC (NAC)
  6. MYB
  • WRKY:

WRKY TFs are regulatory component of plant responses to pathogen.  WRKY33 play a role in plant defense against necrotrophic pathogens (Zheng et al., 2006). The expression of WRKY70 is activated by SA and repressed by JA. WRKY70 can function either as a positive or as a negative regulator of PR gene expression (Li et al., 2004).   

  • APETALA2 (AP2)/ ETHYLENE RESPONSIVE FACTOR (ERF):

Transcription factors AP2/ERFs regulates plant developmental processes and their response to biotic and abiotic stresses (Saleh and Pages 2003).

AP2/ERFs contain four subfamilies (Sakuma et al., 2002):

  1. APETALA2 (AP2)
  2. RELATED TO ABSCISIC ACID INSENSITIVE3/VIVIPAROUS1 (RAV)
  3. DEHYDRATION RESPONSIVE ELEMENT BINDING proteins (DREBs) (subgroup A1-A6)
  4. ETHYLENE RESPONSIVE FACTORS (ERFs) (subgroup V-X)

Ethylene Responsive Factor (ERF1) and (ERF6) in Arabidopsis regulates defense gene expression and resistance to the necrotrophic fungal pathogen Botrytis cinerea (Berrocal-Lobo et al., 2002; Meng et al., 2013).

  • NAC :

The NAC (NAM, ATAF and CUC) family is plant specific group of TFs. The NAC acronym is derived from three genes that initially contain a particular domain (the NAC domain): NAM (for no apical meristem), ATAF1 and -2 and CUC (for cup-shaped cotyledon). Some NAC TFs can act as a positive or negative regulators of the plant defense responses (Yuan et al., 2019). Kaneda et al. (2009) reported the over expression of Os NAC4 (rice NAC4) that leads to hypersensitive response (HR) cell death accompanied by the loss of plasma membrane integrity, nuclear DNA fragmentation and typical morphological changes.  

  • BASIC LEUCINE ZIPPER DOMAIN (bZIP):

Basic Leucine Zipper Domain TF have ability to regulate genes associated with PAMP-triggered immunity, effector-triggered immunity and hormonal signaling network (Noman et al., 2017). The best known bZIP involved in plant defense belong to the TGA family. TGA2 and NON EXPRESSER OF PR GENE1 (NPR1) are activator of systemic acquired resistance (SAR). During SAR TGA2 recruits NPR1 as part of enhanceosome (Boyle et al., 2009).  Nuclear localization of NPR1 is essential for induction of PR genes (Kinkema et al., 2000).

  • BASIC HELIX-LOOP-HELIX (bHLH):

The bHLH transcription factor MYC2 acts as a master regulator of JA signaling pathway and can control the crosstalk between JA and other hormone signaling pathway. MYC2 can physically interact with other key regulatory proteins to form heterodimers with other TFs, it also has ability to activate or repress gene expression in response to multiple signals (Kazan and Manners 2013). Fernandez-Calvo et al. (2011) reported that MYC3 and MYC4 are activators of JA-regulated program that function along with MYC2 to regulate different subset of the JA-dependent transcriptional response.

  • MYB:

In plant MYB TFs regulate biotic and abiotic stresses. Segarra et al. (2009) reported MYB72 functions as a node of convergence in the signalling pathway that are induced by the different beneficial microorganisms. MYB96 is a molecular link that mediates ABA-SA crosstalks. Observation of Seo and Park (2010) indicate that MYB96 – mediated abscisic acid (ABA) signals enhance plant disease resistance by inducing SA biosynthesis.  Raffaele et al. (2006) demonstrated that Arabidopsis thaliana MYB30 (AtMYB30) expression in response to an HR-inducing bacterial pathogen is dependent on SA accumulation but NPR1 independent.  

Plants have survival strategy relying on gene regulation by transcription factor.

References:

Berrocal-Lobo, M., Molina, A. and Solano, R. 2002 Constitutive Expression of ETHYLENE-RESPONSE FATOR1 in Arabidopsis Confers  Resistance to Several Necrotrophic Fungi. The Plant Journ.  29(1): 23 – 32

doi.org/10.1046/j.1365-313x.2002.01191.x

Boyle, P., Su, E. L., Rochon, A., Shearer, H. L., Murmu, J., Chu, J. Y., Fobert, P. R. and Despres, C. 2009 The BTB/POZ Domain of the Arabidopsis Disease Resistance Protein NPR1 Interacts with the Repression Domain of TGA2 to Negate its Function [W]. Plant Cell 21(11): 3700 – 3713

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Fernandez-Calvo, P., Chini, A., Fernandez-Barbero, G., Chico, J. M., Gimenez-Ibanez,S., Geerinck, J., Eeckhout, D., Schweizer, F., Godoy, M., Franco-Zorrilla, J. M., Pauwels, L., Witters, E., Puga, M. I., Paz-Ares, J., Goossens, A., Reymond, P., De, J.G. and Solano, R. 2011 The Arabidopsis bHLH Transcription Factors MYC3 and MYC4 are Targets of JAZ Repressors and Act Additively with MYC2 in the Activation of Jasmonate Responses. Plant Cell 23(2): 701 -715

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Goldfarb, A. N. and Lewandowska, K. 1994 Nuclear Redirection of a Cytoplasmic Helix-Loop-Helix Protein via Heterodimerization with a Nuclear Localizing Partner. Exp. Cell Res. 214(2): 481 – 485

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Kaneda, T., Taga, Y., Takai, R., Iwano, M., Matsui, H., Takayama, S., Isogai, A. and Che, F-S. 2009 The Transcription Factor OsNAC4 is a Key Positive Regulator of Plant Hypersensitive Cell Death. EMBO 28(7): 926 – 936

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Karin, M. and Hunter, T. 1995   Transcriptional Control by Protein Phosphorylation: Signal Transmission from the Cell Surface to the Nucleus. Curr. Biol. 5(7): 747 – 757

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Kosugi, S., Hasebe, M., Matsumura, N., Takashima, H., Miyamoto-Sato,  E., Tomita, M. and Yanagawa, H. 2009 Six Classes of Nuclear Localization Signals Specific to Different Binding Grooves of Importin α. Jour. Biological Chem. 284(1): 478 – 481

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Kazan, K. and Manners, J. M. 2013 MYC2: The Master in Action. Mol. Plant 6(3): 686 – 703

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Li, J., Brader, G. and Palva, E. T. 2004 The WRKY 70 Transcription Factor: A Node of Convergence for Jasmonate-Mediated and Salicylate-Mediated Signals in Plant Defense. Plant Cell 16(2): 319 – 313

doi: 10.1105/tpc.016980

Liu, L., White, M. J. and MacRae, T. H. 1999 Transcription Factors and their Genes in Higher Plants Functional Domains, Evolution and Regulation. Eur. J. Biochem. 262(2): 247 – 257

doi: 10.1046/j.1432-1327.1999.00349.x

Liu, Y., Li, P., Li, F. and Wu, M. 2018 The Nuclear Transportation Routes of Membrane-Bound Transcription Factors. Cell Commun. Signal 16: 12

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Meng, X., Xu, J., He, Y., Yang, K-Y., Mordorski, B., Liu, Y and Zhang, S. 2013 Phosphorylation of an ERF Transcription Factor by Arabidopsis MPK3/MPK6 Regulates Plant Defense Gene Induction and Fungal Resistance[C][W]. Plant Cell 25(3): 1126 – 1142

doi: 10.1105/tpc.112.109074

Noman, A., Liu, Z., Aqeel, M., Zainab, M., Khan, M. I., Hussain, A., Ashraf, M. F., Li, X., Weng, Y. and He, S. 2017 Basic Leucine Zipper Domain Transcription Factors: The Vanguards in Plant Immunity. Biotechnol. Lett. 39(12): 1779 – 1791

doi: 10.1007/s10529-017-2431-1

Raffaele, S., Rivas, S. and Roby, D. 2006 An Essential Role for Salicylic Acid in AtMYB30-Mediated Control of the Hypersensitive Cell Death Program in Arabidopsis. FEBS Letters 580: 3498 – 3504

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Sakuma, Y., Liu, Q., Dubouzet, J. G., Abe, H., Shinozaki, K. and Yamaguchi-Shinozaki, K. 2002 DNA-binding Specificity of the ERF/AP2 Domain of Arabidopsis DREBs, Transcription Factors Involved in Dehydration and Cold-Inducible Gene Expression. Biochem. Biophys. Res. Commun. 290(3): 998 – 1009

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Segarra, G., Van der Ent, S., Trillas, I. and Pieterse, C. M. 2009 MYB72 a Node of Convergence in Induced Systemic Resistance Triggered by a Fungal and a Bacterial Beneficial Microbe. Plant Biol. 11(1): 90 – 96

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Yuan, X., Wang, H., Cai, J., Li, D. and Song, F. 2019 NAC Transcription Factors in Plant Immunity. Phytopathol. Res. 1: 3

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Zheng, Z., Qamar, S. A., Chen, Z. and Mengiste, T. 2006 Arabidopsis WRKY 33 Transcription Factor is Required for Resistance to Necrotrophic Fungal Pathogens. The Plant Journal 48: 592 – 605

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