Specificity versus redundancy in the RAP2.4 transcription factor family of Arabidopsis thaliana: transcriptional regulation of genes for chloroplast peroxidases

Abstract

BackgroundThe Arabidopsis ERFIb / RAP2.4 transcription factor family consists of eight members with highly conserved DNA binding domains. Selected members have been characterized individually, but a systematic comparison is pending. The redox-sensitive transcription factor RAP2.4a mediates chloroplast-to-nucleus redox signaling and controls induction of the three most prominent chloroplast peroxidases, namely 2-Cys peroxiredoxin A (2CPA) and thylakoid- and stromal ascorbate peroxidase (tAPx and sAPx).To test the specificity and redundancy of RAP2.4 transcription factors in the regulation of genes for chloroplast peroxidases, we compared the DNA-binding sites of the transcription factors in tertiary structure models, analyzed transcription factor and target gene regulation by qRT-PCR in RAP2.4, 2-Cys peroxiredoxin and ascorbate peroxidase T-DNA insertion lines and RAP2.4 overexpressing lines of Arabidopsis thaliana and performed promoter binding studies.ResultsAll RAP2.4 proteins bound the tAPx promoter, but only the four RAP2.4 proteins with identical DNA contact sites, namely RAP2.4a, RAP2.4b, RAP2.4d and RAP2.4h, interacted stably with the redox-sensitive part of the 2CPA promoter. Gene expression analysis in RAP2.4 knockout lines revealed that RAP2.4a is the only one supporting 2CPA and chloroplast APx expression. Rap2.4h binds to the same promoter region as Rap2.4a and antagonizes 2CPA expression. Like the other six RAP2.4 proteins, Rap2.4 h promotes APx mRNA accumulation. Chloroplast ROS signals induced RAP2.4b and RAP2.4d expression, but these two transcription factor genes are (in contrast to RAP2.4a) insensitive to low 2CP availability, and their expression decreased in APx knockout lines. RAP2.4e and RAP2.4f gradually responded to chloroplast APx availability and activated specifically APx expression. These transcription factors bound, like RAP2.4c and RAP2.4g, the tAPx promoter, but hardly the 2CPA promoter.ConclusionsThe RAP2.4 transcription factors form an environmentally and developmentally regulated transcription factor network, in which the various members affect the expression intensity of the others. Within the transcription factor family, RAP2.4a has a unique function as a general transcriptional activator of chloroplast peroxidase activity. The other RAP2.4 proteins mediate the fine-control and adjust the relative availability of 2CPA, sAPx and tAPx.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-017-1092-5) contains supplementary material, which is available to authorized users.

Cold-priming of chloroplast ROS signalling is developmentally regulated and is locally controlled at the thylakoid membrane

“…Secondly, the lability of tAPX makes priming depended on de-novo synthesis of tAPX. Transcription in the nucleus, translation in the cytosol, protein import into chloroplasts and embedding of tAPX into the thylakoid membrane enable fine-tuning and cross-talk with other signalling processes 38,39,65,91–93 . Thirdly, tAPX controls an electron dissipation pathway subordinated to thioredoxin and NADP + reduction 94,95 .…”

Overexpression of a Phosphate Starvation Response AP2/ERF Gene From Physic Nut in Arabidopsis Alters Root Morphological Traits and Phosphate Starvation-Induced Anthocyanin Accumulation

“…Products of the RAP2.4 genes participate in cell dedifferentiation, water balance and oxidative stress responses ( Lin R.C. et al, 2008 ; Iwase et al, 2011 ; Rae et al, 2011 ; Zhu et al, 2014 ; Rudnik et al, 2017 ). Constitutive overexpression of At1g78080 causes defects in numerous developmental processes regulated by light and ethylene, including root elongation and root hair formation ( Lin R.C.…”

AP2/ERF Transcription Factor Regulatory Networks in Hormone and Abiotic Stress Responses in Arabidopsis

“…Overexpression of TRANSLUCENT GREEN ( TG ) resulted in vitrified leaves with increased water content in cells, leading to increased drought tolerance (Zhu et al, 2014). TG regulates cell water homeostasis mainly by directly activating several aquaporin genes (Rae et al, 2011; Zhu et al, 2014), as well as Ascorbate Peroxidases ( APx ) genes encoding chloroplast peroxidases that functions to protect against photo-oxidative stresses caused by Reactive Oxygen Species (ROS) (Rudnik et al, 2017).…”