SRFR1, a suppressor of effector‐triggered immunity, encodes a conserved tetratricopeptide repeat protein with similarity to transcriptional repressors

Abstract

SummaryEffector-triggered immunity provides plants with strong protection from pathogens. However, this response has the potential to be highly deleterious to the host and needs to be tightly controlled. The molecular mechanisms in the plant that regulate the balance between activation and suppression of resistance are not fully understood. Previously, we identified Arabidopsis suppressor of rps4-RLD 1 (srfr1) mutants with enhanced resistance to the bacterial effector AvrRps4. These mutants were recessive and retained full susceptibility to virulent bacteria, suggesting that SRFR1 functions as a negative regulator and that AvrRps4-triggered immunity was specifically enhanced in the mutants. Consistent with this, we show here that the response to flagellin, an elicitor of basal resistance, is unaltered in srfr1-1. In contrast, resistance to AvrRps4 in srfr1-1 requires EDS1, a central regulator of effector-triggered immunity via multiple resistance genes. SRFR1 is a single-copy gene encoding a pioneer tetratricopeptide repeat protein conserved between plants and animals. The SRFR1 tetratricopeptide repeat domain shows sequence similarity to those of transcriptional repressors in Saccharomyces cerevisiae and Caenorhabditis elegans. Indeed, a sub-pool of SRFR1 transiently expressed in Nicotiana benthamiana leaf cells localizes to the nucleus. Identification of SRFR1 may therefore provide insight into the regulation of the transcriptional reprogramming that is activated by effector-triggered immunity.

Chromatin Configuration as a Battlefield in Plant-Bacteria Interactions

“…SRFR1 (for SUPPRESSOR OF RPS4-RLD1) was identified as a negative regulator of defense-related gene expression in Arabidopsis (Kim et al, , 2010Kwon et al, 2009). SRFR1 is located in both cytoplasm and nucleus and possibly possesses dual functions.…”

Ubiquitination during Plant Immune Signaling

“…Therefore, the F-box protein CPR1 targeted SNC1 and RPS2 for degradation, thereby regulating their protein levels and preventing autoimmunity. SNC1 and RPS4 were also subject to negative regulation by SUPPRESSOR OF RPS4-RLD1 (SRFR1), a tetratricopeptide repeat protein with similarity to nuclear transcriptional repressors (Kwon et al, 2009;Kim et al, 2010;Li et al, 2010). Interestingly, SRFR1 interacted with SUPPRES-SOR OF THE G2 ALLELE OF SKP1 (SGT1) whereas CPR1 interacted with multiple ASK proteins (Gou et al, 2009;Li et al, 2010).…”

Resistance to the Pseudomonas syringae Effector HopA1 Is Governed by the TIR-NBS-LRR Protein RPS6 and Is Enhanced by Mutations in SRFR1

“…Similar to RPS4 and other TNL genes, RPS6 generates alternatively spliced transcripts, although the alternative transcript structures are RPS6 specific. To illustrate the value of comparative studies between RPS6 and RPS4, we tested the effects of mutations in SRFR1, a negative regulator of AvrRps4-triggered immunity (Kwon et al, 2009), on rps6 mutants. Interestingly, mutations in SRFR1 also enhanced HopA1-triggered immunity in rps6 mutants, indicating a more general function of SRFR1 in regulating ETI.…”