The N-Terminus of the Floral Arabidopsis TGA Transcription Factor PERIANTHIA Mediates Redox-Sensitive DNA-Binding.

Nora Gutsche,Sabine Zachgo

doi:10.1371/journal.pone.0153810

Abstract

The Arabidopsis TGA transcription factor (TF) PERIANTHIA (PAN) regulates the formation of the floral organ primordia as revealed by the pan mutant forming an abnormal pentamerous arrangement of the outer three floral whorls. The Arabidopsis TGA bZIP TF family comprises 10 members, of which PAN and TGA9/10 control flower developmental processes and TGA1/2/5/6 participate in stress-responses. For the TGA1 protein it was shown that several cysteines can be redox-dependently modified. TGA proteins interact in the nucleus with land plant-specific glutaredoxins, which may alter their activities posttranslationally. Here, we investigated the DNA-binding of PAN to the AAGAAT motif under different redox-conditions. The AAGAAT motif is localized in the second intron of the floral homeotic regulator AGAMOUS (AG), which controls stamen and carpel development as well as floral determinacy. Whereas PAN protein binds to this regulatory cis-element under reducing conditions, the interaction is strongly reduced under oxidizing conditions in EMSA studies. The redox-sensitive DNA-binding is mediated via a special PAN N-terminus, which is not present in other Arabidopsis TGA TFs and comprises five cysteines. Two N-terminal PAN cysteines, Cys68 and Cys87, were shown to form a disulfide bridge and Cys340, localized in a C-terminal putative transactivation domain, can be S-glutathionylated. Comparative land plant analyses revealed that the AAGAAT motif exists in asterid and rosid plant species. TGA TFs with N-terminal extensions of variable length were identified in all analyzed seed plants. However, a PAN-like N-terminus exists only in the rosids and exclusively Brassicaceae homologs comprise four to five of the PAN N-terminal cysteines. Redox-dependent modifications of TGA cysteines are known to regulate the activity of stress-related TGA TFs. Here, we show that the N-terminal PAN cysteines participate in a redox-dependent control of the PAN interaction with a highly conserved regulatory AG cis-element, emphasizing the importance of redox-modifications in the regulation of flower developmental processes.

Highlights

Angiosperm flowers are commonly composed of sepals, petals, stamens and carpels and variations in the number and shape of these organs contribute to generate the enormous flower diversity
Plant-specific TGA transcription factor (TF) exert their activity by binding to characteristic cis-elements in regulatory regions of target genes comprising the TGACG core sequence [3]
Electrophoretic mobility shift assays (EMSAs) were conducted to analyze the ability of PAN to bind to two known TGA TF response elements comprising the TGACG binding site

Summary

Introduction

Angiosperm flowers are commonly composed of sepals, petals, stamens and carpels and variations in the number and shape of these organs contribute to generate the enormous flower diversity. The TGA TF family of Arabidopsis consists of 10 members known to participate in flower developmental and stress response processes [2]. They execute their activity by binding to cis-regulatory elements comprising the name-giving TGACG core recognition sequence. A well-characterized TGA TF binding element is the activation sequence-1 (as-1) motif, first described in bacterial and viral promoters [3] Variations of this motif, named as-1-like motifs, are present in promoter regions of various stress-related plant genes, such as PATHOGENESIS-RELATED GENE1 (PR1) or GLUTATHIONE-S-TRANSFERASE (GST) [4,5,6,7,8]. The second AG intron comprises binding sites for other key floral regulators such as WUSCHEL and LEAFY and serves as a crucial hub integrating different signals to mediate a complex expression regulation [9, 11]

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