The tryptophan pathway is involved in the defense responses of rice against pathogenic infection via serotonin production

Abstract

SummaryThe upregulation of the tryptophan (Trp) pathway in rice leaves infected by Bipolaris oryzae was indicated by: (i) enhanced enzyme activity of anthranilate synthase (AS), which regulates metabolic flux in the Trp pathway; (ii) elevated levels of the AS (OASA2, OASB1, and OASB2) transcripts; and (iii) increases in the contents of anthranilate, indole, and Trp. The measurement of the contents of Trp-derived metabolites by highperformance liquid chromatography coupled with tandem mass spectrometry revealed that serotonin and its hydroxycinnamic acid amides were accumulated in infected leaves. Serotonin accumulation was preceded by a transient increase in the tryptamine content and by marked activation of Trp decarboxylase, indicating that enhanced Trp production is linked to the formation of serotonin from Trp via tryptamine. Feeding of radiolabeled serotonin to inoculated leaves demonstrated that serotonin is incorporated into the cell walls of lesion tissue. The leaves of a propagating-type lesion mimic mutant (sl, Sekiguchi lesion) lacked both serotonin production and deposition of unextractable brown material at the infection sites, and showed increased susceptibility to B. oryzae infection. Treating the mutant with serotonin restored deposition of brown material at the lesion site. In addition, the serotonin treatment suppressed the growth of fungal hyphae in the leaf tissues of the sl mutant. These findings indicated that the activation of the Trp pathway is involved in the establishment of effective physical defenses by producing serotonin in rice leaves.

ATAF2, a NAC Transcription Factor, Binds to the Promoter and Regulates NIT2 Gene Expression Involved in Auxin Biosynthesis

“…And lesion formation, wounding, and pathogen infection also activate tryptophan-dependent IAA biosynthesis pathways (Normanly and Bartel, 1999;Zhao and Last, 1996). Furthermore, the tryptophan biosynthesis pathway is also involved in the defense responses (Ishihara et al, 2008). Thus, we can postulate that ATAF2 might regulate auxin biosynthesis pathway and this regulation could be connected with ATAF2-mediated plant defense system.…”

Accumulation of 9- and 13-KODEs in response to jasmonic acid treatment and pathogenic infection in rice

“…Bipolaris oryzae (MAFF 305067) was provided by the NIAS Genebank (http://www.gene.affrc.go.jp/index_en.php). B. oryzae inoculation was performed as previously described by Ishihara et al (2008). 11) 3.…”

“…B. oryzae inoculation was performed as previously described by Ishihara et al (2008). 11) 3. Chemicals JA was prepared by alkaline hydrolysis of methyl jasmonate (Tokyo Chemical Industry, Tokyo, Japan).…”

“…7,8) In rice (Oryza sativa), JA has been considered a central player in signal transduction from the recognition of pathogen infection to the biosynthesis of defensive metabolites, such as terpenoid and flavonoid phytoalexins, 9,10) serotonin, and phenylamides. 11,12) The active form of JA is the amide with L-isoleucine, 13,14) which is formed by jasmonate resistance 1 (JAR1). 15) 12-Oxo-phytodienoic acid (12-OPDA), an intermediate compound in jasmonic acid biosynthesis, also serves as a signal mediator in an overlapping but distinct way from JA.…”

Regulatory roles of serotonin and melatonin in abiotic stress tolerance in plants

“…7,8 A surge in the activity of anthranilate synthase ( EC : 4.1.3.27) and accumulation of tryptophan-derived metabolites (including serotonin) has been observed in the leaves of rice plants in response to biotic stress. 78 Recent reports based on gene annotation and analysis of metabolic pathway network database (RiceCyc) in rice have further shown that TDC1 and TDC3 are induced by abiotic and biotic stress factors. 9 Melatonin biosynthesis and its regulation involve the activity of enzymes downstream to serotonin biosynthesis, namely serotonin N-acetyltransferase (SNAT, E.C.…”