A highly conserved NB-LRR encoding gene cluster effective against <it>Setosphaeria turcica </it>in sorghum

<p>Abstract</p> <p>Background</p> <p>The fungal pathogen <it>Setosphaeria turcica </it>causes turcicum or northern leaf blight disease on maize, sorghum and related grasses. A prevalent foliar disease found worldwide where the two host crops, maize and sorghum are grown. The aim of the present study was to find genes controlling the host defense response to this devastating plant pathogen. A cDNA-AFLP approach was taken to identify candidate sequences, which functions were further validated via virus induced gene silencing (VIGS), and real-time PCR analysis. Phylogenetic analysis was performed to address evolutionary events.</p> <p>Results</p> <p>cDNA-AFLP analysis was run on susceptible and resistant sorghum and maize genotypes to identify resistance-related sequences. One CC-NB-LRR encoding gene <it>GRMZM2G005347 </it>was found among the up-regulated maize transcripts after fungal challenge. The new plant resistance gene was designated as <it>St </it>referring to <it>S. turcica</it>. Genome sequence comparison revealed that the CC-NB-LRR encoding <it>St </it>genes are located on chromosome 2 in maize, and on chromosome 5 in sorghum. The six <it>St </it>sorghum genes reside in three pairs in one locus. When the sorghum <it>St </it>genes were silenced via VIGS, the resistance was clearly compromised, an observation that was supported by real-time PCR. Database searches and phylogenetic analysis suggest that the <it>St </it>genes have a common ancestor present before the grass subfamily split 50-70 million years ago. Today, 6 genes are present in sorghum, 9 in rice and foxtail millet, respectively, 3 in maize and 4 in <it>Brachypodium distachyon</it>. The <it>St </it>gene homologs have all highly conserved sequences, and commonly reside as gene pairs in the grass genomes.</p> <p>Conclusions</p> <p>Resistance genes to <it>S. turcica</it>, with a CC-NB-LRR protein domain architecture, have been found in maize and sorghum. VIGS analysis revealed their importance in the surveillance to <it>S. turcica </it>in sorghum. The <it>St </it>genes are highly conserved in sorghum, rice, foxtail millet, maize and Brachypodium, suggesting an essential evolutionary function.</p>