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The avrRxo1 Gene from the Rice Pathogen Xanthomonas oryzae pv. oryzicola Confers a Nonhost Defense Reaction on Maize with Resistance Gene Rxo1

July 2004 , Volume 17 , Number  7
Pages  771 - 779

Bingyu Zhao , 1 Edna Y. Ardales , 1 , 2 Asuncion Raymundo , 3 Jianfa Bai , 1 Harold N. Trick , 1 Jan E. Leach , 1 and Scot H. Hulbert 1

1Department of Plant Pathology, 4024 Throckmorton Plant Sciences Center, Kansas State University, Manhattan 66506-5502; 2Department of Plant Pathology and 3Institution of Biological Sciences, University of the Philippines, Los Baños, Laguna, The Philippines

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Accepted 11 February 2004.

Maize lines that contain the single dominant gene Rxo1 exhibit a rapid hypersensitive response (HR) after infiltration with the rice bacterial streak pathogen Xanthomonas oryzae pv. oryzicola, but not with the rice bacterial blight pathogen X. oryzae pv. oryzae. The avirulence effector gene that corresponds to Rxo1, designated avrRxo1, was identified in an X. oryzae pv. oryzicola genomic library. When introduced into X. oryzae pv. oryzae, clones containing avrRxo1 induced an HR on maize with Rxo1, but not on maize without Rxo1. The avrRxo1 gene is 1,266 bp long and shows no significant homology to any database sequences. When expressed in an X. oryzae pv. oryzae hrpC mutant that is deficient in the type III secretion system, avrRxo1 did not elicit the HR, indicating that the avrRxo1-Rxo1 interaction is dependent on type III secretion. Transient expression of avrRxo1 in onion cells after biolistic delivery revealed that the protein product was associated with the plasma membrane. Transient expression in maize lines carrying Rxo1 resulted in cell death, suggesting that AvrRxo1 functions from inside maize cells to elicit Rxo1-dependent pathogen recognition.

Additional keywords: bacterial leaf streak, nonhost resistance.

© 2004 The American Phytopathological Society