A key enzyme for flavin synthesis is required for nitric oxide  and reactive oxygen species production in disease resistance.
Nitric oxide (NO) and reactive oxygen species (ROS) play key roles in plant immunity. However, the regulatory mechanisms of the production of these radicals are not fully understood. Hypersensitive response (HR) cell death requires the simultaneous and balanced production of NO and ROS. In this study we indentified NbRibAencoding a bifunctional enzyme, guanosine triphosphate cyclohydrolase II/3,4-dihydroxy-2-butanone-4-phosphate synthase, which participates in the biosynthesis of flavin, by screening genes related to mitogen-activated protein kinase-mediated cell death, using virus-induced gene silencing. Levels of endogenous riboflavin and its derivatives, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are important prosthetic groups for several enzymes participating in redox reactions, decreased in NbRibA-silenced Nicotiana benthamiana. Silencing NbRibA compromised not only HR cell death, but also the NO and ROS production induced by INF1 elicitin and a constitutively active form of NbMEK2 (NbMEK2DD), and also induced high susceptibility to oomycete Phytophthora infestans and ascomycete Colletotrichum orbiculare. Compromised radical production and HR cell death induced by INF1 in NbRibA-silenced leaves were rescued by adding riboflavin, FMN or FAD. These results indicate that flavin biosynthesis participates in regulating NO and ROS production, and HR cell death.
Asai
Shuta
S
Laboratory of Defense in Plant-Pathogen Interactions, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan.
Mase
Keisuke
K
Yoshioka
Hirofumi
H
D016923:Cell Death; D005415:Flavins / Q000096:biosynthesis*; D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D020868:Gene Silencing; D017343:Genes, Plant; D007113:Immunity, Innate; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009569:Nitric Oxide / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000276:immunology
D005415:Flavins; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D009569:Nitric Oxide; D019751:Intramolecular Transferases; C066493:L-3,4-dihydroxy-2-butanone-4-phosphate synthase