Inducible overexpression of a rice allene oxide synthase gene increases the endogenous jasmonic acid level, PR gene expression, and host resistance to fungal infection.
Many studies in dicotyledonous plants have shown that jasmonates, including jasmonic acid (JA) and methyl jasmonate, are important signal molecules involved in induced resistance to pathogen infection and insect herbivory. However, very little genetic and molecular evidence is available to demonstrate their role in host defense response of rice and other economically important monocot plants. In this study, we have shown that exogenous application of JA was able to activate defense gene expression and local induced resistance in rice seedlings against the rice blast fungus (Magnaporthe grisea). Furthermore, we have characterized a pathogen-inducible rice OsAOS2 gene (which encodes allene oxide synthase, a key enzyme in the JA biosynthetic pathway) and examined the role of endogenous JA in rice defense response through transgenic manipulation of the JA biosynthesis. Sequence analysis indicated that OsAOS2 contains four common domains of the cytochrome P450 enzyme, but does not have the signal peptide for chloroplast targeting. The basal level of OsAOS2 expression is very low in leaves but relatively high in the sheath, culm, and flower of rice plants. Interestingly, the expression of OsAOS2 in rice leaves can be induced significantly upon M. grisea infection. Transgenic rice lines carrying the OsAOS2 transgene under the control of a strong, pathogen-inducible PBZ1 promoter accumulated abundant OsAOS2 transcripts and higher levels of JA, especially after the pathogen infection. These transgenic lines also exhibited enhanced activation of pathogenesis-related (PR) genes such as PR1a, PR3, and PR5 and increased resistance to M. grisea infection. Our results suggest that JA plays a significant role in PR gene induction and blast resistance in rice plants.
Mei
Chuansheng
C
Department of Plant Pathology and Program in Cell and Molecular Biology, University of Arkansas, Fayetteville 72071, USA.
Qi
Min
M
Sheng
Guangyao
G
Yang
Yinong
Y
D000595:Amino Acid Sequence; D003517:Cyclopentanes / Q000378:metabolism* / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate / Q000502:physiology; D019746:Intramolecular Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020082:Magnaporthe / Q000502:physiology; D008969:Molecular Sequence Data; D012275:Oryza / Q000187:drug effects / Q000235:genetics* / Q000382:microbiology*; D054883:Oxylipins; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D020539:Sequence Analysis, Protein; D015533:Transcriptional Activation
D003517:Cyclopentanes; D054883:Oxylipins; D010940:Plant Proteins; C011006:jasmonic acid; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase