Abstract
Serotonin is a well known neurotransmitter in mammals and plays an important role in various mental functions in humans. In plants, the serotonin biosynthesis pathway and its function are not well understood. The rice sekiguchi lesion (sl) mutants accumulate tryptamine, a candidate substrate for serotonin biosynthesis. We isolated the SL gene by map-based cloning and found that it encodes CYP71P1 in a cytochrome P450 monooxygenase family. A recombinant SL protein exhibited tryptamine 5-hydroxylase enzyme activity and catalyzed the conversion of tryptamine to serotonin. This pathway is novel and has not been reported in mammals. Expression of SL was induced by the N-acetylchitooligosaccharide (chitin) elicitor and by infection with Magnaporthe grisea, a causal agent for rice blast disease. Exogenously applied serotonin induced defense gene expression and cell death in rice suspension cultures and increased resistance to rice blast infection in plants. We also found that serotonin-induced defense gene expression is mediated by the RacGTPase pathway and by the G alpha subunit of the heterotrimeric G protein. These results suggest that serotonin plays an important role in rice innate immunity.
Highlights
Plants have developed various immune responses to protect themselves from pathogen attack [1]
Because our results suggest that serotonin plays a role in rice innate immunity, we examined whether serotonin treatment of rice seedlings (ϳ1 month old) had any effect on infection with a compatible race of M. grisea
Tryptophan hydroxylase belongs to a family of aromatic amino acid hydroxylases and requires iron and the coenzyme tetrahydropterin for catalytic activity [29]
Summary
Plants have developed various immune responses to protect themselves from pathogen attack [1]. Applied serotonin induced defense gene expression and cell death in rice suspension cultures and increased resistance to rice blast infection in plants. These results suggest that serotonin plays an important role in rice innate immunity.
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