Lr1-mediated leaf rust resistance pathways of transgenic wheat lines revealed by a gene expression study using the Affymetrix GeneChipA® Wheat Genome Array

The wheat gene Lr1 imparts resistance to certain races of the leaf rust pathogen Puccinia triticina. However, the biological basis underlying the complex resistance mechanisms remains largely unknown. Gene expression profiling analyses using the Affymetrix GeneChip(A (R)) Wheat Genome Array were performed with six independent Lr1 transgenic lines sampled before inoculation (0 h) and at 6 and 24 h post-inoculation (HPI) with the avirulent P. triticina race CCDS. For the 6- and 24-HPI time points, 3,384 probe sets corresponding to 2,976 transcripts were expressed differentially compared with the plants before inoculation. Genes involved in defence signalling are triggered as early as 6 HPI and include COI1, the primary component of jasmonic acid signalling. By 24 HPI, a shift in plant cellular metabolism, namely carbon conservation, is notable. The enzymes of glycolysis and gluconeogenesis are down-regulated; however, enzymes linked to alternative carbon sequestration processes such as the glyoxylate cycle are up-regulated. Also at 24 HPI, secondary signalling molecules belonging to the various hormone signalling pathways were triggered. These microarray data suggest that the Lr1-mediated leaf rust resistance is achieved by early onset of defence signalling followed by a coordinated interplay of metabolism alteration and elicitation of defence responses.