Expression analysis of defense-related genes in Zingiber (Zingiberaceae) species with different levels of compatibility to the soft rot pathogen Pythium aphanidermatum.

Ginger (Zingiber officinale Roscoe) cultivars are susceptible to soft rot disease caused by Pythium aphanidermatum. We analyzed changes in transcript levels of 41 genes in the highly susceptible ginger cultivar varada, a less susceptible wild accession (wild ginger), and a Pythium aphanidermatum-resistant relative, Z. zerumbet, following treatment with Pythium aphanidermatum or one of three signaling molecules: salicylic acid (SA), jasmonic acid (JA), or ethylene (ET). The 41 studied genes were chosen because they are known to be involved in the hypersensitive response (HR), cell signaling, or host defense. Expression of most genes peaked within 24 h of Pythium aphanidermatum infection. Interestingly, the level of induction was typically manyfold higher in Z. zerumbet than in wild ginger. However, several HR genes that were significantly induced in wild ginger were not induced in Z. zerumbet. Most of the genes, including those involved in signaling, did not respond to any of the three signaling molecules in Z. zerumbet while several genes responded to all the three signaling molecules in varada. In wild ginger, a large proportion of the genes responded to ET, but not to SA or JA. These results suggest that different mechanisms govern the three pathosystems. Resistance in Z. zerumbet seems to be independent of HR and the tested signaling molecules, whereas both mechanisms appear to be activated in the tolerance reaction of wild ginger. This work revealed potential defense components of this understudied tropical taxa, and will contribute to the design of strategies for transgenic improvement of ginger.