Rice Lesion Mimic Mutant (LMM) 6321-2 Exhibits Resistance Against Rice Blast (Magnaporthe oryzae) via Increased Hypersensitive Response

Publisher: Bicol University PDF

Abstract

Hypersensitive response (HR) is a key feature of plant immunity that sacrifices through programmed cell death (PCD) the already infected cells and thereby restricts the growth and further invasion of pathogens. Rice (Oryza sativa) lesion mimic mutants (LMM) manifest disease phenotype in the absence of pathogen and are monocots’ model organisms in unraveling the molecular mechanism of HR-induced PCD. The LMM 6321-2 used in this study was from an ethyl methanesulfonate-generated mutant accession obtained from IRRI, Philippines and was phenotypically and genetically characterized. It was an initiator type of LMM with significantly reduced agronomic yield potential. However, LMM 6321-2 exhibited increased or partial resistance against virulent rice blast fungus, Magnaporthe oryzae (PO6-6 and CA89 isolates) and induced HR-mediated PCD after avirulent isolate (V86010, CA41 and M101- 1-2-9-1) inoculation using rice blast nursery spray and punch inoculation assays. Segregation analysis using the F2 population showed LMM 6321-2 to be a single recessive mutation. Expression profiling of PCD-associated genes showed significant changes in its expression profile both in non-inoculated setup and M. oryzae post-inoculated experiments where genes of NADPH oxidases, reactive oxygen species (ROS) scavengers, LMM-, phytohormone-, senescence- and pathogenesis-related genes were found to be significantly expressed with a different timing of expression than its IR64 parent. In brief, the mutant showed delayed expression of PCD-related genes peaking 48 hours post-inoculation (hpi) compared to IR64, which heightened 24 hpi. Taken together, it was hypothesized that LMM 6321-2 have a ROSmediated PCD where the mutation plays a key role in the lesion mimicking phenotype.