Gene expression profiles unique to chile (Capsicum annuum L.) resistant to Phytophthora root rot

Transcriptome profiling in chile (Capsicum annuum) roots was used to determine those genes with expression profiles correlated with a resistance phenotype to the pathogen, Phytophthora capsici. Two microarrays were generated; a 10K element array printed with cDNAs from a library of transcripts expressed in Criollo de Morelos-334 variety of C. annuum 6 h post-challenge with P. capsici and a 2K element array printed with sequenced cDNA clones selected based on their preliminary patterns of expression. This second array was enriched for clones that were differentially expressed in susceptible (New Mexico 6-4) vs. resistant (CM334) varieties of C. annuum. Gene expression profiles were revaluated at 0, 4 and 24 h post-inoculation. Control treatments included samples collected at 0, 4, and 24 h post-mock-inoculation. In addition to the parental CM334, a resistant backcross line (01-1688) was also used to identify gene expression patterns associated with the resistance phenotype. Based on a principal component analysis, CM334 samples showed the most significant transcription induction at 4 and 24 h post-inoculation, while the predominant variability in the susceptible line was in genes repressed at 24 h. A set of 168 genes with significant changes in expression following P. capsici challenge was identified; of these, 22 were uniquely expressed only in the resistant lines (CM334 or 01-1688). This set of genes represent candidates for further study as markers for recurrent selection programs and as candidate genes for the mechanism of disease resistance.