Molecular plant-microbe interactions : MPMI 2016
Ethylene biosynthesis and signaling is required for rice immune response and basal resistance against Magnaporthe oryzae infection.
Recent studies have suggested that ethylene enhances host resistance to fungal pathogen Magnaporthe oryzae, the causal agent of rice blast disease. Among the six ACS genes in rice, OsACS1 and OsACS2 are induced within 24 hours of inoculation by M. oryzae. This induction occurs simultaneously with an increase in ethylene production that is noticeable 12 hours post inoculation. The purpose of this study was to examine the dynamics of ethylene production and signaling in wild type and RNAi-mediated suppression lines deficient in ethylene production (acs2) or signaling (eil1) after challenge with M. oryzae, as well as fungal cell wall elicitors. Ethylene-insensitive mutant lines show an attenuated basal defense response including lower basal expression of the genes encoding a chitin-binding receptor, pathogenesis-related (PR) proteins, and the enzymes involved in the synthesis of diterprenoid phytoalexins, a reduction on early HR-like cell death, and reduced incidence of callose deposition. Ethylene-deficient mutants showed an intermediate phenotype, with a significant reduction in expression of defense-related genes and callose deposition, but only a slight reduction in HR-like cell death. As a result, all ethylene-insensitive mutants show increased susceptibility to M. oryzae, whereas the ethylene-deficient lines show a slight, but less significant increase in disease severity. These results show that ethylene signaling, and to some extent ethylene production, are required for rice basal resistance against the blast fungus, Magnaporthe oryzae.