Karin Schlangen

Induction of antimicrobial 3-deoxyflavonoids in pome fruit trees controls fire blight.

Abstract Fire blight, a devastating bacterial disease in pome fruits, causes severe economic losses worldwide. Hitherto, an effective control could only be achieved by using antibiotics, but this implies potential risks for human health, livestock and environment. A new approach allows transient inhibition of a step in the flavonoid pathway, thereby inducing the formation of a novel antimicrobial 3-deoxyflavonoid controlling fire blight in apple and pear leaves. This compound is closely related to natural phytoalexins in sorghum. The approach does not only provide a safe method to control fire blight: Resistance against different pathogens is also induced in other crop plants.

Polyphenol metabolism provides a screening tool for beneficial effects of Onobrychis viciifolia (sainfoin)

Onobrychis viciifolia (sainfoin) is a traditional fodder legume showing multiple benefits for the environment, animal health and productivity but weaker agronomic performance in comparison to other legumes. Benefits can be mainly ascribed to the presence of polyphenols. The polyphenol metabolism in O. viciifolia was studied at the level of gene expression, enzyme activity, polyphenol accumulation and antioxidant activity. A screening of 37 accessions regarding each of these characters showed a huge variability between individual samples. Principal component analysis revealed that flavonols and flavan 3-ols are the most relevant variables for discrimination of the accessions. The determination of the activities of dihydroflavonol 4-reductase and flavonol synthase provides a suitable screening tool for the estimation of the ratio of flavonols to flavan 3-ols and can be used for the selection of samples from those varieties that have a specific optimal ratio of these compounds for further breeding.

'Le Rouge et le Noir': A decline in flavone formation correlates with the rare color of black dahlia (Dahlia variabilis hort.) flowers

BackgroundMore than 20,000 cultivars of garden dahlia (Dahlia variabilis hort.) are available showing flower colour from white, yellow and orange to every imaginable hue of red and purple tones. Thereof, only a handful of cultivars are so-called black dahlias showing distinct black-red tints. Flower colour in dahlia is a result of the accumulation of red anthocyanins, yellow anthochlors (6’-deoxychalcones and 4-deoxyaurones) and colourless flavones and flavonols, which act as copigments. White and yellow coloration occurs only if the pathway leading to anthocyanins is incomplete. Not in all cultivars the same step of the anthocyanin pathway is affected, but the lack of dihydroflavonol 4-reductase activity is frequently observed and this seems to be based on the suppression of the transcription factor DvIVS. The hitherto unknown molecular background for black colour in dahlia is here presented.ResultsBlack cultivars accumulate high amounts of anthocyanins, but show drastically reduced flavone contents. High activities were observed for all enzymes from the anthocyanin pathway whereas FNS II activity could not be detected or only to a low extent in 13 of 14 cultivars. cDNA clones and genomic clones of FNS II were isolated. Independently from the colour type, heterologous expression of the cDNA clones resulted in functionally active enzymes. FNS II possesses one intron of varying length. Quantitative Real-time PCR showed that FNS II expression in black cultivars is low compared to other cultivars. No differences between black and red cultivars were observed in the expression of transcription factors IVS and possible regulatory genes WDR1, WDR2, MYB1, MYB2, 3RMYB and DEL or the structural genes of the flavonoid pathway. Despite the suppression of FHT expression, flavanone 3-hydroxylase (FHT, synonym F3H) enzyme activity was clearly present in the yellow and white cultivars.ConclusionsAn increased accumulation of anthocyanins establishes the black flowering phenotypes. In the majority of black cultivars this is due to decreased flavone accumulation and thus a lack of competition for flavanones as the common precursors of flavone formation and the anthocyanin pathway. The low FNS II activity is reflected by decreased FNS II expression.

Multiple evolution of flavonoid 3′,5′-hydroxylase

AbstractMain conclusionMultiple F3′5′H evolution from F3′H has occurred in dicotyledonous plants. Efficient pollinator attraction is probably the driving force behind, as this allowed for the synthesis of delphinidin-based blue anthocyanins. The cytochrome P450-dependent monooxygenases flavonoid 3′-hydroxylase (F3′H) and flavonoid 3′,5′-hydroxylase (F3′5′H) hydroxylate the B-ring of flavonoids at the 3′- and 3′- and 5′-position, respectively. Their divergence took place early in plant evolution. While F3′H is ubiquitously present in higher plants, the distribution of F3′5′H is scattered. Here, we report that F3′5′H has repeatedly evolved from F3′H precursors at least four times in dicotyledonous plants: In the Asteraceae, we identified F3′5′Hs specific for the subfamilies Cichorioideae and Asteroideae, and additionally an F3′5′H that seems to be specific for the genus Echinops of the subfamily Carduoideae; moreover, characterisation of a sequence from Billardiera heterophylla (formerly Sollya heterophylla) (Pittosporaceae) showed that the independent evolution of an F3′5′H has occurred at least once also in another family. The evolution of F3′5′H from an F3′H precursor represents a gain of enzymatic function, probably triggered by an amino acid change at one position of substrate recognition site 6. The gain of F3′5′H activity allows for the synthesis of delphinidin-based anthocyanins which usually provide the basis for lilac to blue flower colours. Therefore, the need for an efficient pollinator attraction is probably the driving force behind the multiple F3′5′H evolution.

Note added in proof to: Over-expression of an FT-homologous gene of apple induces early flowering in annual and perennial plants

In the study presented, we concluded on the basis of the data publicly available at the time of submission that the isolated FT-like mRNA sequences are alleles of one and the same MdFT gene. Based on this conclusion, we designated both sequences as alleles of MdFT1 and used the sequence with strongest identity to FT of Arabidopsis for transformation. Based on the information published very recently by Kotoda et al. (2010), we learnt that the sequence (accession number HQ424012) used for transformation of Arabidopsis, apple and poplar in our study was MdFT2 (linkage group 4) and not MdFT1 (linkage group 12) as assumed. Based on the high level of sequence identity between both MdFT genes, the primers used for expression studies do not distinguish between MdFT1 and MdFT2. Therefore, the expression pattern shown in Fig. S1 contains both mRNA sequences (MdFT1 and MdFT2). Also Fig. 6 showing multiple sequence alignment of two segments of the fourth exon is corrected conveniently. Whether the two amino acid substitutions (A157S and A158V) present in MdFT1 but not in MdFT2 will have any effect on the phenotype of transgenic poplar cannot be stated at the moment. Further investigations are needed. Corrected Fig. 6 and legend are given below.