Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2008
Publication Date: 3/1/2008
Citation: Costanzo, S., Wang, X., Jia, Y. 2008. Analysis of the effectiveness of the rice blast resistance gene Pi-ta. In: Proceedings of the 32nd Rice Technical Working Group Meetings, February 18-21, 2008, San Diego, CA. 2008. CDROM. Interpretive Summary:
Technical Abstract: The casual agent of rice blast, Magnaporthe oryzae, continues to remain a serious threat for rice production and in general for the world food supply. The most economically and environmentally viable strategy to control this pathogen is the development of cultivars which possess major resistance genes conferring resistance to predominant races of M. oryzae. However, it is also well-known that the resistance based on a single major gene can be easily overcome in a few years after its deployment. The major blast resistance gene Pi-ta, originally introduced from a Vietnamese variety Tetep, has been bred into several US elite cultivars, Katy, Madison, Kaybonnet, Drew, Ahrent, Cybonnet and Spring. Some of these cultivars have been commercialized for over a decade with little incidence of blast disease, while others were short lived after their initial deployment. In order to investigate the molecular mechanisms of the stability of resistance based on Pi-ta, an extensive study is being undertaken including the detailed characterization of the possible protein variants that are produced by the Pi-ta gene in different genetic backgrounds by alternative splicing. Alternative splicing is an important mechanism that allows multiple transcripts and protein diversity being generated from the same DNA sequence of a single gene. This process has been previously reported in several plant genes and gene families. However, recent computational and experimental studies suggest this event could play a significant role in plant resistance genes enhancing protein diversity against their pathogen counterpart. Using reverse transcription PCR to study expression levels of a major blast resistance gene Pi-ta during infection, we detected two differentially processed RNA transcripts of this gene. Transcripts detected in this study encode two open reading frames (ORF). One ORF is with 2787 bp with two exons and one intron encoding the Pi-ta protein, and another ORF with 3102 bp was discovered with four exons and three introns. These two ORFs each encode a centrally located NB-ARC domain while one of them (the Pi-ta protein) is lacking a C-terminus thioredoxin domain. The biological significance of this important mechanism in the Pi-ta gene is currently under investigation. Particularly, we would like to determine if the presence of both variants is required to obtain effective resistance, and if both are involved in resistance in different genetic backgrounds.