Isolation of a cDNA encoding a novel leucine-rich repeat motif from Sorghum bicolor inoculated with fungi.

A sorghum cDNA clone has been isolated that encodes a protein containing six imperfect leucine-rich repeats (LRRs) of approximately 22 amino acids in length. The putative protein, designated SLRR, also contains a signal peptide, and six potential N-glycosylation sites. Comparisons of SLRR and its LRR consensus sequences found significant homology to the extracellular binding domains of receptor-protein kinases RLK5 and TMK1 of Arabidopsis, and some plant disease resistance genes. Results from RNA gel blot analyses showed that SLRR mRNA accumulates rapidly in mesocotyls and juvenile leaves by 6 h postinoculation with the fungus Colletotricum graminicola. Further experiments suggest that the gene encoding SLRR is neither systemically induced by fungal inoculation, nor transcriptionally activated in a host-fungal-pathogen-specific manner. The presence of LRRs strongly suggests that the SLRR protein is involved in protein-ligand binding and therefore may be a component of a signal transduction pathway.