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HPR1 Is Required for Immune Response in Arabidopsis
HPR1 is required for immune response in Arabidopsis
Powdery mildew pathogens are agriculturally important fungi that infect many crops, such as wheat and barley, causing great yield losses worldwide. Previously, EDR1 (Enhanced Disease Resistance 1) was reported as a key negative regulator of plant-powdery mildew interaction. The edr1 mutant displays powdery mildew-induced cell death phenotype and is more resistant to powdery mildew infection. In addition, edr1 shows an enhanced leaf senescence phenotype when treated with ethylene. EDR1 encodes a protein kinase, which has a conserved C-terminal kinase domain and an N-terminal regulatory domain.
  To study the mechanism of EDR1-regulated immune response and programed cell death, scientists in Dr. Dingzhong Tang’s lab from the Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences preformed a suppressor screen for the edr1 mutant. In this screen, Dr. Tang’s lab identified the hpr1-4 mutation, which suppresses the powdery mildew-induced cell death phenotype and the disease resistance phenotype of edr1. Furthermore, hpr1-4 suppresses edr1-mediated disease resistance to other pathogens. However, the hpr1-4 mutation enhances the ethylene-induced leaf senescence phenotype of edr1. The hpr1-4 single mutant is more susceptible to powdery mildew and several other biotrophic pathogens. The hpr1-4 single mutant also shows hypersensitive ethylene-induced leaf senescence phenotype.
HPR1 is a component of the Arabidopsis THO/TREX complex. The THO/TREX complex is a conserved protein complex among yeast, metazoan and plants. In yeast and metazoan, the THO/TREX complex is a conserved regulator of the mRNA export pathway. In the Poly (A) RNA in situ hybridization assay, mRNA was accumulated in the nucleus of hpr1-4 single mutant, indicated that hpr1-4 has defection in mRNA export. This work suggests that the Arabidopsis THO/TREX complex is required for mRNA export and implies a general link between mRNA export and disease resistance in plants.
This work has recently been published online on The Plant Journal (DOI: 10.1111/j.1365-313X.2011.04835.x), with Huairong Pan, a graduate student from Dr. Dingzhong Tang’s lab, as the first author. This research was supported by grants from National Basic Research Program of China, National Natural Science Foundation of China and National Transgenic Program of China.
Dingzhong Tang, Ph.D.
Institute of Genetics and Developmetnal Biology, Chinese Academy of Sciences, Beijing, China.

(Image by Huairong Pan etc.)
Figure. hpr1-4 is defective in mRNA export.
Small leaves (<5 mm) from wild type Col-0, edr1, hpr1-4 edr1 and hpr1-4 were fixed and probed with fluorescence-probed oligo (dT). Images were taken of cells at the center of the leaf. Green spots correspond to the localization of mRNA, which accumulated at higher levers in the nuclei of hpr1-4 edr1 and hpr1-4 cells. Bars= 40 µM. Experiments were repeated three times with similar results.