Rice plant accumulates serotonin in response to pathogen attack. sl mutant that is deficient in the conversion of tryptamine to serotonin accumulates tryptamine instead of serotonin in the leaves inoculated with Bipolaris oryzae. The accumulation of tryptamine was accompanied by a marked increase in indole-3-acetic acid (IAA) concentration in the leaves. We investigated the effects of inoculation of other pathogenic fungi and treatment of elicitor. The accumulation of IAA was induced by inoculation of B. sorokiniana, but the inoculation of Magnaporthe grisea and treatment of CuCl_2 was ineffective, indicating that the IAA accumulation is not necessarily linked to induction of defense responses. In addition, we found that when tryptamine was supplemented to the medium, B. oryzae converted it to IAA. These findings suggested that the accumulation of IAA in the sl leaves was the result of the conversion of tryptamine to IAA by B. oryzae. We further examined the effects of tryptamine and serotonin on the growth of B. oryzae for understanding of the physiological significance of the conversion. The growth of B. oryzae was significantly inhibited by high concentrations of trypamine and serotonin. We also found that B. oryzae converted serotonin to 5-hydroxy IAA. It is thus likely that the conversion of indole amines to corresponding carboxylic acids is the detoxification process of indole amines in B. oryzae.

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Black spot disease, which is caused by a Japanese pear pathotype of Alternaria alternata (Fr.) Keissler, is one of the most serious diseases in Japanese pear cultivation in Japan and the commercial cultivars 'Nijisseiki', 'Shinsui' and 'Nansui' are susceptible. The causal pathogen produces a host-specific toxin named AK-toxin, which causes necrosis on fruit skin and leaves resulting in decreased yield. AK-toxin is toxic to susceptible cultivars only and is harmless to resistant cultivars and non-host plants. Ethylene is known to play major roles in regulating plant defense responses against various pathogens. Here, we investigated the relationship between ethylene synthesis and black spot disease in 'Nijisseiki' pear leaves by treatment with an analog of ethylene and 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action. Interestingly, both treatments enhanced black spot disease symptoms. Both treatments also increased ethylene production in accordance with disease symptoms via altered gene expression of ethylene biosynthetic enzymes, especially ACC synthase genes.

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Plant cells generate high-level of Biophotons during elicitor response. We previously found that plant activators and defense-related plant hormones (eg. PBZ, BTH, SA, JA) prime rice cells for enhanced generation of chitin elicitor responsive Biophotons. The chitin elicitor responsive Biophotons were generated through phospholipid signaling in close association with production of H_2O_2, a signal molecule in stress responses. Here we report that sublethal treatment of rice cells with thermal and osmotic stresses potentiate chitin elicitor responsive Biophotons. Sublethal abiotic stress treatment primes plant cells to survive in lethal stresses (so-called "acclimation"). We also found that abscisic acid, a plant stress hormone, also showed potentiation activity of elicitor-responsive Biophotons. These results indicate that not only biotic stress resistance, but also abiotic stress resistance in plant could be reflected on the potentiation of elicitor-responsive Biophotons. It is estimated that signal crosstalk between biotic and abiotic stress response underlies this phenomenon. By applying this phenomenon on the screening of compounds library, we have found some compounds which protect plants from heat stress disorder. This work was supported by Adaptable and Seamless Technology Transfer Program through target-driven R&D, JST.

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The stringent response is one of the most significant and well-investigated gene regulatory systems in bacteria. The signaling molecule for the stringent response is guanosine 5'-diphosphate 3'-diphosphate (ppGpp). Recently, RelA/SpoT homolog genes (RSHs and CRSHs), which encode ppGpp synthase, have been identified in plants. The accumulation of ppGpp is stimulated by stressful conditions and plant hormones such as abscisic acid or jasmonic acid in plants. A database search revealed the presence of several putative RelA/SpoT homologs in the moss Physcomitrella patens. Two RelA/SpoT homolog genes designated PpRSH1 and PpRSH2, which are involved in the synthesis of ppGpp, were isolated from P patens. Complementary analysis of PpRSH1 and PpRSH2 in E. coli showed that these genes had ppGpp synthetic activity. Additionally recombinant PpRSH1 and PpRSH2 were shown to synthesize ppGpp in vitro. Both proteins were revealed to be localized in chloroplasts. The expression of PpRSH genes were induced upon treatment with abscisic acid or by abiotic stresses such as dehydration and UV irradiation. However jasmonic acid and high concentration of salt did not elevate the expression of PpRSH genes unlike those of RSH genes in flowering plants. The overexpression mutant for PpRSH1 resulted in enhancement of gametophore development. These results suggest that PpRSHs play an important role in stress adaptation and development in P patens.

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Tuliposides are major secondary metabolites in tulip (Tulipa gesneriana). Their lactonized aglycons, tulipalins, function as defensive chemicals due to their biological activities. We recently found that tuliposide conversion to tulipalin occurs enzymatically in tulip tissues, and the enzyme, tuliposide-converting enzyme (TCE), has been purified from tulip bulbs. However, the results raised a possibility that the TCE that is expressed in tissues other than bulbs is different from bulb TCE. To investigate the functional diversity of tulip TCE, the enzyme was first purified from petals as a representative for tissues other than bulbs. The purified enzyme preferentially accepted tuliposides as substrates, with 6-tuliposide A the best substrate, which allowed naming the enzyme 'tuliposide A-converting enzyme (TCEA)', and exhibited characteristics similar to bulb enzyme. However, specific activity and molecular mass differed significantly between the petal and bulb enzymes. Following peptide sequencing, novel cDNA (TgTCEA) encoding petal TCEA was isolated, and the functional characterization of the recombinant enzyme confirmed the involvement of TgTCEA in 6-tuliposide A conversion to tulipalin A. TgTCEA was transcribed in all tulip tissues, but not in bulbs, indicating the presence of a bulb-specific TgTCEA. The enzyme, TgTCEA, was the first identified member of the lactoneforming carboxylesterases, specifically catalyzing intramolecular transesterification.

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Steroidal saponins have various biological activities. Steroidal saponins are often found in monocotyledons such as plants of the families Dioscoreaceae, Agavaceae, and Liliaceae. In particular, the rhizomes of Dioscorea, known as yam, contain furostane and spirostane glycosides such as protodioscin and dioscin, respectively. These steroid saponins are derived from choresterol by sequential modification with oxygenation and transglycosylation reaction as shown in Figure 1. Namely, several P450s are likely involved in oxygenations at the C-16, C-22, and C-26 positions, and UGTs will function in transglycosylation at C-3 and C-26. But little is known about enzyme and genes for dioscin biosynthesis. To investigate steroidal saponin biosynthesis in Dioscorea spp., we performed comparative transcriptome analysis of the rhizomes of Dioscorea spp. We will utilize these datasets to identify key genes for cholesterol and dioscin biosynthesis, and will apply the results to plant metabolic engineering of steroidal saponins.

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Oleuropein, a secoiridoid glycoside, found in several Oleaceae species such as the olive tree and privet tree. Oleuropein has several hydroxyl moieties, caffeoyl group and glucose group. The olive tree (Olea europaea) is a species of small tree in Oleaceae species, and olive fruit is of major agricultural importance in the word as the source of olive oil. Olive leaves and fruits contain up to 8% oleuropein in the wet weight. Oleurpein are stable, does not have any of the activities, and is kept in the vacuoles or cytosol of the leaf cell. With damaged by herbivore, enzymatic activity localized in organelles separate from oleuropein starts to activate oleuropein into a very strong protein denaturant that has glutaraldehyde-like structure by enzyme such as β-glucosidase (β-GH) and polyphenol oxidase that localized in organelles separated from the iridoid glycoside. As a result, the activated iridoid glycoside has adverse effects against herbivores by decreasing the nutritive value of plant protein. Nevertheless the activation pathway has not been clearly proven yet. To investigate the physiological function of iridoid glycoside in chemical defense, we determined chemical structure of oleuropein hydrolyzed metabolite (OHM) by LC-MS/MS and NMR.

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2-Phenylethanol (2PE) is a prominent scent compound in roses. We have demonstrated that 2PE is produced without loss of the α-position hydrogen from L-[^2H_8]Phenylalanine (L-[^2H_8]Phe) by feeding experiments. In 2008-2011, we found [^2H_7]-2PE production in rose protoplast harvested from May to October. We, here aimed the functional characterization of novel 2PE biosynthetic pathway producing [^2H_7]-2PE. Feeding experiments of L-[^2H_8]Phe to rose protoplast revealed that [^2H_7]-2PE was hardly synthesized in the period from November to April. We characterized two enzymes (aminotransferase and decarboxylase) involving each step in the novel pathway. RNA interference on the biosynthetic enzyme reduced 2PE production. These results suggested that [^2H_7]-2PE is transformed from L-[^2H_8]Phe by the action of aminotransferase and decarboxylase.

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