Elicitor induced activation of the methylerythritol phosphate pathway toward phytoalexins biosynthesis in rice

Abstract

Diterpenoid phytoalexins such as momilactones and phytocassanes are produced via geranylgeranyl diphosphate in suspension-cultured rice cells after treatment with a chitin elicitor. We have previously shown that the production of diterpene hydrocarbons leading to phytoalexins and the expression of related biosynthetic genes are activated in suspension-cultured rice cells upon elicitor treatment. To better understand the elicitor-induced activation of phytoalexin biosynthesis, we conducted microarray analysis using suspension-cultured rice cells collected at various times after treatment with chitin elicitor. Hierarchical cluster analysis revealed two types of early-induced expression (EIE-1, EIE-2) nodes and a late-induced expression (LIE) node that includes genes involved in phytoalexins biosynthesis. The LIE node contains genes that may be responsible for the methylerythritol phosphate (MEP) pathway, a plastidic biosynthetic pathway for isopentenyl diphosphate, an early precursor of phytoalexins. The elicitor-induced expression of these putative MEP pathway genes was confirmed by quantitative reverse-transcription PCR. 1-Deoxy-D: -xylulose 5-phosphate synthase (DXS), 1-deoxy-D: -xylulose 5-phosphate reductoisomerase (DXR), and 4-(cytidine 5'-diphospho)-2-C-methyl-D: -erythritol synthase (CMS), which catalyze the first three committed steps in the MEP pathway, were further shown to have enzymatic activities that complement the growth of E. coli mutants disrupted in the corresponding genes. Application of ketoclomazone and fosmidomycin, inhibitors of DXS and DXR, respectively, repressed the accumulation of diterpene-type phytoalexins in suspension cells treated with chitin elicitor. These results suggest that activation of the MEP pathway is required to supply sufficient terpenoid precursors for the production of phytoalexins in infected rice plants.

Characterization of an Elicitor-Induced Rice WRKY Gene,OsWRKY71

“…15) The following oligonucleotide sequences were used: Ubiquitin, functions as a repressor, we speculate that the activation of defense-related genes by overexpressed OsWRKY71 is indirect. In a previous microarray analysis using suspension-cultured rice cells treated with chitin oligosaccharide elicitor, 21) it was found that the mRNA levels of genes encoding the above chitinases, PR-5, and peroxidases showed changes similar to that of OsWR-KY71, or delayed changes, further confirming the involvement of OsWRKY71 in the activation of defense-related genes.…”

“…15) As for the results of microarray analysis, a total of 64 genes were down-regulated, and 21 genes of the 64 genes were also down-regulated by chitin oligosaccharide elicitor treatment. 21) One-third of the 21 down-regulated genes are of unknown function, and the other two-thirds included genes likely to be related to metabolism, regulation of gene expression, and signal transduction, but the biological functions of these down-regulated genes in defense responses remain unknown. On the other hand, a total of 200 genes were up-regulated in the OsWR-KY71-overexpressing transgenic rice cells, and 146 of the 200 up-regulated genes were also up-regulated by chitin oligosaccharide elicitor treatment.…”

“…On the other hand, a total of 200 genes were up-regulated in the OsWR-KY71-overexpressing transgenic rice cells, and 146 of the 200 up-regulated genes were also up-regulated by chitin oligosaccharide elicitor treatment. 21) One-third of the 146 up-regulated genes are of unknown function, and the other two-thirds include genes likely to be related to metabolism, regulation of gene expression, defense, transport, and signal transduction. Because WRKY proteins have been investigated extensively for their possible involvement in defense responses, we focused next on defense-related genes among the 146 up-regulated genes.…”

Allelopathic momilactones A and B are implied in rice drought and salinity tolerance, not weed resistance

“…Since momilactones A and B were first discovered by Kato et al (1973), major research has been conducted on the two compounds concentrated on plant growth and pathogen (Fukuta et al 2007;Okada et al 2007;Hasegawa et al 2010), and antioxidant capacity (Fukuta et al 2007), cytotoxic and antitumor activity (Kim et al 2007), whereas other biological activities of momilactones A and B have remained unknown. This study is the first to demonstrate that momilactones A and B correlated to the tolerance of drought and salinity in much stronger levels than the weed tolerance in rice.…”

“…1) against the fungal rice blast disease pathogen Magnaporthe oryzae in rice leaves and straw (Cartwright et al 1977(Cartwright et al , 1981. The function of momilactone A as a phytoalenxin was extensively studied against fungal pathogens (Fukuta et al 2007;Okada et al 2007;Hasegawa et al 2010), whereas momilactone B was much less described (Fukuta et al 2007). Among potential growth inhibitors detected in rice including phenolic acids, fatty acids, phenylalkanoic acids, hydroxyamic acids, terpenes, and indoles, momilactones A and B particularly play a critical role (Kato-Noguchi and Peters 2013).…”