ACD6, a Novel Ankyrin Protein, Is a Regulator and an Effector of Salicylic Acid Signaling in the Arabidopsis Defense Response

Abstract

The previously reported Arabidopsis dominant gain-of-function mutant accelerated cell death6-1 ( acd6-1 ) shows spontaneous cell death and increased disease resistance. acd6-1 also confers increased responsiveness to the major defense signal salicylic acid (SA). To further explore the role of ACD6 in the defense response, we cloned and characterized the gene. ACD6 encodes a novel protein with putative ankyrin and transmembrane regions. It is a member of one of the largest uncharacterized gene families in higher plants. Steady state basal expression of ACD6 mRNA required light, SA, and an intact SA signaling pathway. Additionally, ACD6 mRNA levels were increased in the systemic, uninfected tissue of Pseudomonas syringae -infected plants as well as in plants treated with the SA agonist benzothiazole (BTH). A newly isolated ACD6 loss-of-function mutant was less responsive to BTH and upon P. syringae infection had reduced SA levels and increased susceptibility. Conversely, plants overexpressing ACD6 showed modestly increased SA levels, increased resistance to P. syringae , and BTH-inducible and/or a low level of spontaneous cell death. Thus, ACD6 is a necessary and dose-dependent activator of the defense response against virulent bacteria and can activate SA-dependent cell death.

The Ankyrin-Repeat Transmembrane Protein BDA1 Functions Downstream of the Receptor-Like Protein SNC2 to Regulate Plant Immunity

“…bda1-17D has very similar mutant phenotypes to acd6-1, which also exhibits spontaneous cell death, expresses high levels of PR-1, and displays enhanced pathogen resistance (Rate et al, 1999). Interestingly, the gain-of-function mutation in acd6-1 also occurs in one of the transmembrane domains (Lu et al, 2003). These data suggest that the transmembrane domains of BDA1 and ACD6 play very important roles in the negative regulation of these proteins.…”

“…Among these proteins, only ACD6 and ITN1 have previously been characterized. ACD6 was shown to function as a positive regulator of SA signaling in local defense responses (Lu et al, 2003), whereas ITN1 is involved in salt stress tolerance (Sakamoto et al, 2008). How ACD6 and ITN1 are regulated is unknown.…”

“…[See online article for color version of this figure. ] defense (Lu et al, 2003). Loss-of-function mutations in BDA1 suppress the dwarf morphology and constitutive defense responses in snc2-1D npr1-1 and result in enhanced susceptibility to pathogens.…”

PROHIBITIN3 Forms Complexes with ISOCHORISMATE SYNTHASE1 to Regulate Stress-Induced Salicylic Acid Biosynthesis in Arabidopsis

“…6A), a phenotype that we previously found strongly correlates with 258 hypersusceptibility (e.g. see (Lu et al, 2003;Song et al, 2004;Lee et al, 2007)). 259…”

“…under some conditions, such as nitric oxide with reduced SA production, generated by altered expression/mutation of genes that impact 339 SA biosynthesis, exhibit enhanced susceptibility to virulent and avirulent pathogens, 340 similar to the phenotype of phb3-3 (Delaney et al, 1994;Nawrath and Métraux, 1999;341 Dewdney et al, 2000;Lu et al, 2003;Song et al, 2004;Lee et al, 2007). 342…”