The non-host pathogen Puccinia triticina elicits an active transcriptional response in rice

Rice (Oryza sativa L.) is not susceptible to rust fungi, including the wheat leaf rust fungus Puccinia triticina. Upon inoculation with P. triticina spores, infection hyphae and appressoria were observed on the leaf surfaces of the rice cultivar Nipponbare. The cultivar responded to the inoculation with brown discoloration of the local tissue and fragmentation of rust infection hyphae and appressoria. A microarray gene-expression analysis of the host transcriptional response was performed 24 h after inoculation, revealing rice genes that were up- or down-regulated following the interaction. In particular, the loci represented by five probe sets (Os.55776.1. S1_x_at, Os.55647.1. A1_at, Os.55776.1. S1_at, OsAffx.10944.1. S1_x_at, and OsAffx.10944.1. S1_at) displayed the highest increase in gene expression compared to the control inoculation. The probe sets included members of the receptor-like kinase family (RLK) that occurs within a cluster of RLK genes on chromosome 1. Other RLK genes, within the RLK gene cluster and at another location, also showed increases in gene expression after P. triticina inoculation. The RLK genes varied in response to challenges with different rust strains or when challenged with several non-rust wheat pathogens that are also non-pathogenic to rice. The results indicate that rice has an active transcriptional and possible defense priming reaction in response to P. triticina and other non-host fungal pathogens.