The HSF-like Transcription Factor TBF1 Is a Major Molecular Switch for Plant Growth-to-Defense Transition

Department of Biology, Box 90338, Duke University, Durham, NC 27708, USA.
Current biology: CB (Impact Factor: 9.57). 01/2012; 22(2):103-12. DOI: 10.1016/j.cub.2011.12.015
Source: PubMed


Induction of plant immune responses involves significant transcription reprogramming that prioritizes defense over growth-related cellular functions. Despite intensive forward genetic screens and genome-wide expression-profiling studies, a limited number of transcription factors have been found that regulate this transition.
Using the endoplasmic-reticulum-resident genes required for antimicrobial protein secretion as markers, we identified a heat-shock factor-like transcription factor that specifically binds to the TL1 (GAAGAAGAA) cis element required for the induction of these genes. Surprisingly, plants lacking this TL1-binding factor, TBF1, respond normally to heat stress but are compromised in immune responses induced by salicylic acid and by microbe-associated molecular pattern, elf18. Genome-wide expression profiling indicates that TBF1 plays a key role in the growth-to-defense transition. Moreover, the expression of TBF1 itself is tightly regulated at both the transcriptional and translational levels. Two upstream open reading frames encoding multiple aromatic amino acids were found 5' of the translation initiation codon of TBF1 and shown to affect its translation.
Through this unique regulatory mechanism, TBF1 can sense the metabolic changes upon pathogen invasion and trigger the specific transcriptional reprogramming through its target genes expression.

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Available from: Wei Wang
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    • "Core genes also reflect the conservation of the transition from plant growth to plant defense that is associated with plant responses to biotic stress[39]. In Arabidopsis, this transition is orchestrated by the HEAT SHOCK FACTOR 4 (HSF4), a transcription factor whose expression was upregulated by mite feeding across all three species that acts to repress genes encoding chloroplast proteins[40]. Arrest of the plant growth is also associated with changes in the sugar metabolism (illustrated by the upregulation of a SUGAR TRANSPORT PROTEIN (STP13) required for the retrieval of hexoses from the apoplast across the plasma membrane[32]and cytosolic FRUC- TOSE 1,6-BISPHOSPHATE ALDOLASE (FBA5)[41]involved in the glycolysis), changes in the cell wall properties (seen through the induction of CELLULASE (GH9B8), down-regulation of PECTIN LYASE and expression of genes such as EXORDIUM-LIKE (EXL2), a repressor of growth that is responsive to diminishing energy status in the cell, and GA-STIMULATED ARABI- DOPSIS 6 (GASA6), a hypothetical secreted peptideconservation of defense response to spider mite herbivory across Arabidopsis, grapevine and tomato. a Comparison of DEG detected in response to spider mite herbivory that are orthologous across three species[4,5]. "
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    • "Interestingly, SA and Pseudomonas infection cause DNA damage, such as DNA double strand breaks, suggesting that DNA damage response is an intrinsic component of SA-mediated transcription during plant immunity (Yan et al., 2013; Song and Bent, 2014). Besides functional regulation of transcription factors by NPR1 through complex formation, NPR1 also controls expression of transcription factors, such as WRKY transcription factors, which are required for SA-mediated transcriptional reprogramming (Wang et al., 2006; Pajerowska-Mukhtar et al., 2012). The Arabidopsis genome encodes 74 WRKY factors which bind the specific DNA sequence (C/TTGACT/C), termed the W-box (Rushton et al., 2010). "
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    • "We showed that AED1 transcript accumulation is induced locally and systemically by infection and locally by SA (Figs. 4 and 6). Because the conditional overexpression of AED1-HA repressed both SAR and SA-induced resistance without affecting the growth of Pst in healthy plants (Fig. 5; Supplemental Fig. S7), AED1 might be part of a homeostatic mechanism to limit SAR signaling (Fig. 7) and thus regulate the resource allocation in the tradeoff between defense and plant growth (Heidel and Dong, 2006; van Hulten et al., 2006; Traw et al., 2007; Pajerowska-Mukhtar et al., 2012). In support of this, we found that reduced AED1 transcript levels in Arabidopsis RNAi:AED1/At5g10770 plants caused severe stunting, a phenotype that is often observed in constitutive defense mutants (Shirano et al., 2002; Figure 7. Model integrating EDS1, PAD4, AED1, and LLP1 in SAR signaling. "
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