ARS | Publication request: Alternatively spliced transcripts of Pi-ta blast resistance gene in Oryza sativa

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 29, 2009
Publication Date: September 1, 2009
Citation: Costanzo, S., Jia, Y. 2009. Alternatively spliced transcripts of Pi-ta blast resistance gene in Oryza sativa. Plant Science. 177:468-478.

Interpretive Summary: Plants are capable of defending themselves from the attack of pathogenic organisms using specific sensors (resistance genes), which detect the presence of a pathogen and triggers the defense response. The Pi-ta gene in rice provides resistance to the blast fungus Magnaporthe oryzae. While studying Pi-ta gene activity in rice plants affected by blast disease, we discovered that this gene is able to undergo modifications and produces 12 variants of its original form. These distinct forms could produce at least eight types of sensor (proteins) of different size and potentially with different functions. The present study represents the first report of such a phenomenon in a rice resistance gene. It is very important to understand why and how the plant uses these different sensors for its defense in order to preserve and enhance the defensive mechanisms in rice breeding programs.

Technical Abstract: The Pi-ta gene in rice (Oryza sativa L.) confers resistance to races of Magnaporthe oryzae containing its cognate avirulence gene AVR-Pita. Pi-ta is a single-copy gene belonging to the nucleotide-binding site leucine-rich repeat (NBS-LRR) class of plant resistance (R) genes. In the present study, we report alternative splicing events of Pi-ta, the identification of new introns and novel differentially used splice sites associated with this gene. A total of 12 transcript variants are predicted with ORFs ranging from 945 to 3099 bp and encoding eleven distinct putative products between 315 and 1033 amino acids. Among them, five preserve complete NBS-LRR domains and two couple the original NBS-LRR domain of the Pi-ta protein with a C-terminal thioredoxin (TRX) domain. Gene expression analysis, during the course of a blast infection assay, revealed that transcript variants encoding the TRX domain were constitutively expressed in a resistant Pi-ta containing rice variety, while the other full length or truncated transcripts showed variable levels. These post-transcriptional modifications of Pi-ta produce a series of transcript isoforms that could have a significant role in the R gene regulation and/or may increase protein diversity. To our knowledge, this study represents the first report of alternative splicing of a CC-NBS-LRR gene producing truncated isoforms at both their 5’or 3’ terminus and including transcripts with a TRX domain at their C terminus.