(Homo)glutathione Deficiency Impairs Root-knot Nematode Development in Medicago truncatula

Root-knot nematodes (RKN) are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, RKN induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells essential for nematode growth and reproduction. These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. Detailed analysis of glutathione (GSH) and homoglutathione (hGSH) metabolism demonstrated the importance of these compounds for the success of nematode infection in Medicago truncatula. We reported quantification of GSH and hGSH and gene expression analysis showing that (h)GSH metabolism in neoformed gall organs differs from that in uninfected roots. Depletion of (h)GSH content impaired nematode egg mass formation and modified the sex ratio. In addition, gene expression and metabolomic analyses showed a substantial modification of starch and γ-aminobutyrate metabolism and of malate and glucose content in (h)GSH-depleted galls. Interestingly, these modifications did not occur in (h)GSH-depleted roots. These various results suggest that (h)GSH have a key role in the regulation of giant cell metabolism. The discovery of these specific plant regulatory elements could lead to the development of new pest management strategies against nematodes

Anthocyanin biosynthesis mystery in gerbera cultivars Estelle and Ivory

Flavonoids in our model ornamental plant Gerbera hybrida, consist of three subgroups, flavones, flavonols and anthocyanins. Anthocyanins accumulate in the adaxial surface of petals and give the different cultivars their different color. Both pelargonidin and cyanidin derivatives are found in gerbera, but none of the cultivars contain delphinidin. The acyanic cultivar Ivory is a sport of the pelargonidin containing pink cultivar Estelle, i.e., it originates from an acyanic branch of Estelle. Ivory is apparently a transposon mutant of Estelle, since revertant sectors are regularly observed (Figure 1). In spite of complete loss of anthocyanin pigmentation, all genes encoding enzymes necessary for pelargonidin biosynthesis (PAL, C4H, 4CL, CHS, CHI, F3H, F3’H, DFR, and ANS) are expressed in Ivory at similar levels as in Estelle. We performed a comprehensive flavonoid analysis using UHPLC MS/MS for Estelle and Ivory, collecting samples from whole ray flower petals and from their isolated adaxial epidermi. Except for pelargonidin derivatives, which are present in Estelle but lack nearly completely from Ivory, we found that both cultivars have similar amounts of flavones and flavonoids (mainly apigenin and kaempherol glycosides). We further analyzed the cultivars using RNA sequencing and produced on average 10 million Illumina reads from two developmental stages of Estelle and Ivory petals. Mapping of the reads to an assembly of gerbera Sanger (1), 454 and Illumina reads confirms that all anthocyanidin biosynthesis genes are expressed similarly in the two samples. Surprisingly, none of the assembled contigs show differential expression between these two cultivars. Although dramatically different to the eye, the difference in Estelle and Ivory at transcript level eludes our attempts of analysis. Pelargonidin biosynthesis is intact at least up to the point of dihydrokaempherol synthesis. In reads mapping to transcripts for DFR and ANS we have not observed anomalies that would be indicative of a transposon insertion. None of the glucosyl transferase encoding transcripts are down regulated or anomalous either. However, we do not have biochemical evidence which one of the contigs would encode the gerbera anthocyanidin 3-O-glucosyltransferas

Flavonoid metabolomics in Gerbera hybrida cultivars

Flavonoids, common to all land plants, are synthesized via the phenylpropanoid pathway. Phenylalanine ammonia lyase catalyzes the first reaction of this pathway (conversion of phenylalanine to cinnamate), which is followed by a set of about ten enzymes catalyzing reactions to flavones, flavonols and anthocyanins (Fig.1). Anthocyanin pigments are responsible for pink, orange and purple to blue colors in petals. Flavonoids in our model ornamental plant Gerbera hybrida consist of three subgroups, flavones, flavonols and anthocyanins. Most of the anthocyanins accumulate in the adaxial epidermi of petals and give the different cultivars their different color. Both pelargonidin and cyanidin derivatives are found in gerbera, but none of the cultivars contain delphinidin. According to chromatographic and MS analysis for ray flowers of more than 22 cultivars in different developmental stages, we observed that pelargonidin-type Gerbera cultivars accumulated only the favone apigenin, while cyanidin-type cultivars accumulated luteolin. However, the biosynthesis of flavonols was different, quercetin was observed in both pelargonidin and cyanidin-type cultivars. Based on chemical analysis, RNA sequencing and enzyme assays, we are trying to understand the biosynthetic pathway of flavonoids in differentGerbera cultivars. Different aspects in the timing of gene expression encoding isoenzymes e.g. F3’H and DFR across developmental stages seems important for determination of the flavonoid pattern in the inflorescence