The diversion of 2‐C‐methyl‐d‐erythritol‐2,4‐cyclodiphosphate from the 2‐C‐methyl‐d‐erythritol 4‐phosphate pathway to hemiterpene glycosides mediates stress responses in Arabidopsis thaliana

Abstract

Summary2‐C‐Methyl‐d‐erythritol‐2,4‐cyclodiphosphate (MEcDP) is an intermediate of the plastid‐localized 2‐C‐methyl‐d‐erythritol‐4‐phosphate (MEP) pathway which supplies isoprenoid precursors for photosynthetic pigments, redox co‐factor side chains, plant volatiles, and phytohormones. The Arabidopsis hds‐3 mutant, defective in the 1‐hydroxy‐2‐methyl‐2‐(E)‐butenyl‐4‐diphosphate synthase step of the MEP pathway, accumulates its substrate MEcDP as well as the free tetraol 2‐C‐methyl‐d‐erythritol (ME) and glucosylated ME metabolites, a metabolic diversion also occurring in wild type plants. MEcDP dephosphorylation to the free tetraol precedes glucosylation, a process which likely takes place in the cytosol. Other MEP pathway intermediates were not affected in hds‐3. Isotopic labeling, dark treatment, and inhibitor studies indicate that a second pool of MEcDP metabolically isolated from the main pathway is the source of a signal which activates salicylic acid induced defense responses before its conversion to hemiterpene glycosides. The hds‐3 mutant also showed enhanced resistance to the phloem‐feeding aphid Brevicoryne brassicae due to its constitutively activated defense response. However, this MEcDP‐mediated defense response is developmentally dependent and is repressed in emerging seedlings. MEcDP and ME exogenously applied to adult leaves mimics many of the gene induction effects seen in the hds‐3 mutant. In conclusion, we have identified a metabolic shunt from the central MEP pathway that diverts MEcDP to hemiterpene glycosides via ME, a process linked to balancing plant responses to biotic stress.

The plastidial metabolite 2‐C‐methyl‐D‐erythritol‐2,4‐cyclodiphosphate modulates defence responses against aphids

“…These results indicate that an increased expression of genes in the SA‐signalling pathway induced through an elevation of the MEcPP level does not interfere with the caterpillar‐induced expression of genes in the JA‐signalling pathway or with resistance to P. brassicae caterpillars. Moreover, our results are consistent with previous studies that a high SA level did neither attenuate transcript expression of genes in the JA‐signalling pathway nor the accumulation of JA in plants with high MEcPP levels, that is, hds3 and ceh1 mutant plants (González‐Cabanelas et al, ; Lemos et al, ). It is noteworthy that ceh1 mutant plants used by Lemos et al () are the result of a point mutation in exon 19 at leucine 703 to phenylalanine (Xiao et al, ), whereas the hds3 mutant plants are generated through a point mutation at glycine 696 to aspartic acid in the same exon (Gil et al, ).…”

“…Using Arabidopsis mutant plants accumulating high levels of MEcPP ( hds3 ), we recorded positive impacts of MEcPP on expression levels of genes in SA biosynthetic ( ISOCHORISMATE SYNTHASE1 , ICS1 ), SA responsive ( PATHOGENESIS‐RELATED 1, PR1 ), and SA‐inducible ( PHYTOALEXIN DEFICIENT 4 , PAD4 ) pathways (Figure ). Furthermore, an elevated expression of these genes coincided with enhanced resistance to the B. brassicae aphids in hds3 mutant plants compared with WT plants (Figure a; González‐Cabanelas et al, ). Because the SA‐signalling pathway is known to suppress the JA‐signalling pathway (Kroes et al, ; Mewis et al, ; Walling, ), we probed the impacts of a robust SA‐signalling pathway in hds3 mutant plants on JA‐signalling pathway by assessing JA‐induced plant responses to cabbage white caterpillars ( P. brassicae ).…”

“…Hence, it is important for plants to develop sophisticated mechanisms for synthesis and reallocation of isoprenoid precursors to different tissues under different circumstances in plant life cycles (Flores‐Peréz, Sauret‐Gueto, Gas, Jarvis, & Rodriguez‐Concepcion, ; Li & Sharkey, ; Wright et al, ). It has been hypothesized that plants possess an isolated pool of MEcPP that can be exported from the plastid during an increased metabolite flux through the MEP pathway to protect metabolic flux shifting in the MEP pathway (González‐Cabanelas et al, ; Wright et al, ). It is interesting that we found a significant accumulation of only MEcPP‐ and MEcPP‐related metabolites, whereas other metabolites in the MEP pathway were unaffected after aphid feeding on WT and hds3 plants (Figure ).…”

“…Apart from plant hormones, low‐molecular weight metabolites such as trehalose‐6‐phosphate (T6P) and 2‐ C ‐methyl‐ D ‐erythriol‐2,4‐cyclodiphosphate (MEcPP) have recently been proposed to function as signalling molecules in plant responses to environmental stresses (González‐Cabanelas et al, ; Griffiths et al, ; Singh, Louis, Ayre, Reese, & Shah, ). T6P and trehalose play a role in sugar signalling that mediates responses to (a)biotic stresses as well as growth and development in Arabidopsis and spring wheat (Griffiths et al, ; Schluepmann, Pellny, van Dijken, Smeekens, & Paul, ; Singh et al, ).…”

The Physcomitrella patens Chloroplast Proteome Changes in Response to Protoplastation

“…It has been shown that MEcDP induces the expression of a nuclear stress-related gene that encodes a chloroplast-localized protein in the oxylipin pathway (Xiao Y. et al, 2012). MEcDP accumulation also activates salicylic acid—induced defense responses in Arabidopsis thaliana and enhanced resistance to the phloem-feeding aphid Brevicoryne brassicae (Gonzalez-Cabanelas et al, 2015). We also observed that Pp1s28_399V6 (IPPI) is up-regulated in protoplasts (Supplementary Table 7).…”