Functional Analysis ofAvr9/Cf-9 Rapidly ElicitedGenes Identifies a Protein Kinase, ACIK1, That Is Essential for Full Cf-9–Dependent Disease Resistance in Tomato

Abstract

Tomato (Lycopersicon esculentum) Cf genes confer resistance to the fungal pathogen Cladosporium fulvum through recognition of secreted avirulence (Avr) peptides. Plant defense responses, including rapid alterations in gene expression, are immediately activated upon perception of the pathogen. Previously, we identified a collection of Avr9/Cf-9 rapidly (15 to 30 min) elicited (ACRE) genes from tobacco (Nicotiana tabacum). Many of the ACRE genes encode putative signaling components and thus may play pivotal roles in the initial development of the defense response. To assess the requirement of 42 of these genes in the hypersensitive response (HR) induced by Cf-9/Avr9 or by Cf-4/Avr4, we used virus-induced gene silencing (VIGS) in N. benthamiana. Three genes were identified that when silenced compromised the Cf-mediated HR. We further characterized one of these genes, which encodes a Ser/Thr protein kinase called Avr9/Cf-9 induced kinase 1 (ACIK1). ACIK1 mRNA was rapidly upregulated in tobacco and tomato upon elicitation by Avr9 and by wounding. Silencing of ACIK1 in tobacco resulted in a reduced HR that correlated with loss of ACIK1 transcript. Importantly, ACIK1 was found to be required for Cf-9/Avr9- and Cf-4/Avr4-mediated HRs but not for the HR or resistance mediated by other resistance/Avr systems, such as Pto/AvrPto, Rx/Potato virus X, or N/Tobacco mosaic virus. Moreover, VIGS of LeACIK1 in tomato decreased Cf-9–mediated resistance to C. fulvum, showing the importance of ACIK1 in disease resistance.

Ubiquitination-mediated protein degradation and modification: an emerging theme in plant-microbe interactions

“…They were identified in a cDNA-AFLP analysis of Cf9 tobacco cell cultures treated with Avr9-containing intercellular fluid. Silencing of ACRE189 and ACRE276 dramatically reduced Avr4/Cf4-or Avr9/Cf9-induced HR, apparently suggesting that they are involved in the signaling of Cf4-and Cf9-mediated cell death and/or resistance [45]. However, further studies, such as phenotype of ACRE overexpression plants challenged with Cladosporium fulvum infections should help confirm their role in the regulation of plant defense.…”

Functional analysis of the ABA-responsive protein family in ABA and stress signal transduction in Arabidopsis

“…Another member of the family, tobacco ACRE140, is rapidly activated by Avr9/cf-9 [32]. In rice, Osnop encodes a C2-GRAM domain protein that causes a no pollen phenotype when the gene is deleted [33].…”

Resistance-Gene-Mediated Defense Responses against Biotic Stresses in the Crop Model Plant Tomato

“…Using VIGS in tomato and/or N. bethamiana or N. tobaccum the different components of this interaction have been identified (Figure 1), including Cf-9-interacting thioredoxin (CITRX) [126], Avr9/Cf-9 induced kinase 1 (ACIK1) [127] Likewise, using VIGS in tomato the signaling cascade downstream of Ve1 is shown to require several components including EDS1, NDR1, NRC1, ACIF, MEK2 and SERK3/BAK1 (Figure 1) [135]. To identify additional components involved in Ve1-mediated signaling, a GFPtagged version of Ve1 protein was overexpressed in N. benthamiana leaves, followed by mass spectrometry.…”

“…Using VIGS in tomato and/or N. bethamiana or N. tobaccum the different components of this interaction have been identified (Figure 1), including Cf-9-interacting thioredoxin (CITRX) [126], Avr9/Cf-9 induced kinase 1 (ACIK1) [127], the NLR protein required for HR-associated cell death 1 (NRC1) [128], the U-box protein CMPG1 [129], the LeMPK1, LeMPK2, and LeMPK3 [130], Avr9/Cf-9-Induced F-Box1 (ACIF) [131], members of the phospholipase C family [49], Suppressor of BAK1-Interacting RLK1 1 (SOBIR1) [132], Somatic Embryogenesis Receptor Kinase1 (SERK3)/BAK1 [133], endoplasmic reticulum residing chaperones including HSP70 binding proteins (BiPs) and a lectin-type calreticulin (CRT) [134].…”