ARS | Publication request: Structural and functional analysis of the avirulence gene AVR-Pita1 of the rice blast fungus in isolates of Magnaporthe oryzae worldwide

Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: January 4, 2009
Publication Date: January 10, 2009
Citation: Dai, Y., Jia, Y., Correll, J.C. 2009. Structural and functional analysis of the avirulence gene AVR-Pita1 of the rice blast fungus in isolates of Magnaporthe oryzae worldwide [abstract]. In: Plant and Animal Genome XVII Conference Abstracts. January 10-14, 2009, San Diego, California. P679.

Technical Abstract: The avirulence gene AVR-Pita1 of the rice blast fungus triggers race-specific resistance when races of Magnaporthe oryzae that contain AVR-Pita1 infect rice cultivars that contain the resistance gene Pi-ta. In the present study, a panel of 221 isolates from the US, China, Colombia, Egypt, India and the Philippines were analyzed using sequences of the rDNA-ITS region. A total of 150 isolates were selected for determining the structural and functional properties of AVR-Pita1. Based on pathogenicity tests, it was determined that most of these isolates were avirulent to the Pi-ta containing cultivars. Using the AVR-Pita1 specific primers, an 885bp DNA fragment of the coding region was amplified, and sequenced from the 150 isolates. These AVR-Pita1 DNA sequences were grouped into four major clades. Alignment of all DNA sequences revealed 99% sequence similarity among them, and also when compared with that of O-137, the original isolate where the AVR-Pita1 gene was cloned. Most nucleotide variation at the AVR-Pita1 locus was found in the exons, and most variation in the exons also resulted in amino acid substitutions. In addition, two new nucleotides were identified in the first exon that leads to the frame-shift producing a predicted truncated AVR-Pita1 metalloprotease in five virulent isolates. In other virulent isolates, the functional AVR-Pita1 homologs were predicted to be altered revealed by Southern blot analysis. These data suggest that AVR-Pita1 is under diversified selection. Frame-shift mutation and deletion might be two mechanisms that inactivate AVR-Pita1’s avirulence. Progress in functional analysis of AVR-Pita1 in US virulent isolates by transformation will be presented.