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PLANTS INTERACTING WITH OTHER ORGANISMS

Negative Regulation of Systemic Acquired Resistance by Replication Factor C Subunit3 in Arabidopsis^1,[C],[OA]

Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada (S.X., L.H., X.L.); National Institute of Biological Sciences, Zhongguancun Life Science Park, Beijing 102206, China (S.X., Z.Z., Y.Z.); Hunan Provincial Key Laboratory of Phytohormones and Growth and Development, Hunan Agricultural University, Changsha 410128, China (S.X., L.X.); and Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada (J.-G.C., X.L.)

Systemic acquired resistance (SAR) is a plant immune response induced by local necrotizing pathogen infections. Expression of SAR in Arabidopsis (Arabidopsis thaliana) plants correlates with accumulation of salicylic acid (SA) and up-regulation of Pathogenesis-Related (PR) genes. SA is an essential and sufficient signal for SAR. In a genetic screen to search for negative regulators of PR gene expression and SAR, we found a new mutant that is hypersensitive to SA and exhibits enhanced induction of PR genes and resistance against the virulent oomycete Hyaloperonospora arabidopsidis Noco2. The enhanced pathogen resistance in the mutant is Nonexpressor of PR genes1 independent. The mutant gene was identified by map-based cloning, and it encodes a protein with high homology to Replication Factor C Subunit3 (RFC3) of yeast and other eukaryotes; thus, the mutant was named rfc3-1. rfc3-1 mutant plants are smaller than wild-type plants and have narrower leaves and petals. On the epidermis of true leaves, there are fewer cells in rfc3-1 compared with the wild type. Cell production rate is reduced in rfc3-1 mutant roots, indicating that the mutated RFC3 slows down cell proliferation. As Replication Factor C is involved in replication-coupled chromatin assembly, our data suggest that chromatin assembly and remodeling may play important roles in the negative control of PR gene expression and SAR.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Xin Li (xinli{at}interchange.ubc.ca).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.138321

^* Corresponding author; e-mail xinli{at}interchange.ubc.ca.

Received March 9, 2009; accepted May 27, 2009; published May 29, 2009.