Plant bZIP transcription factors responsive to pathogens: a review

Abstract

Transcription factors of the basic leucine zipper (bZIP) family control important processes in all eukaryotes. In plants, bZIPs are master regulators of many central developmental and physiological processes, including morphogenesis, seed formation, abiotic and biotic stress responses. Modulation of the expression patterns of bZIP genes and changes in their activity often contribute to the activation of various signaling pathways and regulatory networks of different physiological processes. However, most advances in the study of plant bZIP transcription factors are related to their involvement in abiotic stress and development. In contrast, there are few examples of functional research with regard to biotic stress, particularly in the defense against pathogens. In this review, we summarize the recent progress revealing the role of bZIP transcription factors in the biotic stress responses of several plant species, from Arabidopsis to cotton. Moreover, we summarize the interacting partners of bZIP proteins in molecular responses during pathogen attack and the key components of the signal transduction pathways with which they physically interact during plant defense responses. Lastly, we focus on the recent advances regarding research on the functional role of bZIPs in major agricultural cultivars and examine the studies performed in this field.

Figure 1

Relatedness of bZIP proteins from different plant species. The multiple alignment was generated using MUSCLE and the phylogenetic tree was built with the MEGA5 software using the UPGMA method (the numbers at the nodes indicate the bootstrap scores). The bZIP proteins were separated into ten (10) groups, as indicated [7]. The protein accession numbers are indicated in parentheses. The proteins responsive to pathogens are highlighted in bold.

Figure 2

Schematic representation of the diversity of the molecular mechanisms triggered during pathogen defense responses involving bZIP proteins in different plant organisms. (A) The attack of a biotrophic pathogen triggers a signaling pathway mediated by salicylic acid, which alters the redox state of the cell, resulting in the dissociation of the non-expresser of PR (NPR1) protein. The monomer is translocated to the nucleus and activates the expression of SA-responsive genes by interaction with the TGACGTCA cis-element-binding protein (TGA) bZIP transfactors; (B) Recognition of elicitors after pathogen attack promotes the dissociation of the BZI1/ANK1 complex, an event that enables the entry of the BZI1 monomer into the nucleus, favoring the transcriptional regulation of cell death-related genes; (C) Pathogen attack activates a signaling pathway mediated by reactive oxygen species (ROS), resulting in the dissociation of the AtbZIP10/LSD1 complex. AtbZIP10 is then translocated to the nucleus to activate the transcription of HR- and basal defense-related genes; (D) The presence of chitin oligosaccharides induces the expression of the momilactone/phytocassane biosynthetic gene cluster through the activation of the OsTGAP1 bZIP protein; (E) After pathogen invasion, the recognition of elicitors induces the phosphorylation of G/HBF1, which is then translocated to the nucleus, where it regulates the expression of phenylpropanoid biosynthetic genes, such as chalcone synthase. The question marks (?) represent processes or components not yet elucidated.