Changes at a Critical Branchpoint in the Anthocyanin Biosynthetic Pathway Underlie the Blue to Orange Flower Color Transition in Lysimachia arvensis

Abstract

Anthocyanins are the primary pigments contributing to the variety of flower colors among angiosperms and are considered essential for survival and reproduction. Anthocyanins are members of the flavonoids, a broader class of secondary metabolites, of which there are numerous structural genes and regulators thereof. In western European populations of Lysimachia arvensis, there are blue- and orange-petaled individuals. The proportion of blue-flowered plants increases with temperature and daylength yet decreases with precipitation. Here, we performed a transcriptome analysis to characterize the coding sequences of a large group of flavonoid biosynthetic genes, examine their expression and compare our results to flavonoid biochemical analysis for blue and orange petals. Among a set of 140 structural and regulatory genes broadly representing the flavonoid biosynthetic pathway, we found 39 genes with significant differential expression including some that have previously been reported to be involved in similar flower color transitions. In particular, F3′5′H and DFR, two genes at a critical branchpoint in the ABP for determining flower color, showed differential expression. The expression results were complemented by careful examination of the SNPs that differentiate the two color types for these two critical genes. The decreased expression of F3′5′H in orange petals and differential expression of two distinct copies of DFR, which also exhibit amino acid changes in the color-determining substrate specificity region, strongly correlate with the blue to orange transition. Our biochemical analysis was consistent with the transcriptome data indicating that the shift from blue to orange petals is caused by a change from primarily malvidin to largely pelargonidin forms of anthocyanins. Overall, we have identified several flavonoid biosynthetic pathway loci likely involved in the shift in flower color in L. arvensis and even more loci that may represent the complex network of genetic and physiological consequences of this flower color polymorphism.

Chromosome numbers for the Italian flora: 11

“…It displays a petal colour polymorphism. Indeed, blue-and orange-flowered plants occur in monomorphic and polymorphic populations across its native range in Europe (Sánchez-Cabrera et al 2021). The chromosome number 2n = 40, found here in material with orange flowers, agrees with previous reports from Italy and abroad (Löve and Löve 1982;Moneim et al 2003).…”

Beyond Purple Tomatoes: Combined Strategies Targeting Anthocyanins to Generate Crimson, Magenta, and Indigo Fruit

“…The development of P1-producing tomatoes was more challenging, since this class of anthocyanins was completely undetectable in Del/Ros1 fruit, regardless of the presence of a functional F3 5 H. These pigments could be produced only after introduction of the AmDFR gene from snapdragon, which is known to be able to synthesise both C2 and P1 type anthocyanins in flowers of Antirrhinum majus [38,39]. A short region in DFR has been associated with substrate recognition and specific amino acids residues that confer the ability to accept the P1 precursor dihydrokaempferol have been identified [30,40]; more recently, the presence of natural D3-or P1-producing accessions of Lysimachia arvensis has been attributed to the differential expression of two DFR genes encoding enzymes with differences in the substrate binding site [41]. An alignment of the 26 amino acids that form this region is provided in Figure S5, highlighting the role of a specific residue (asparagine in the enzymes able to accept dihydrokaempferol) considered to control substrate recognition.…”

Evolutionary walks through flower color space driven by gene expression in Petunia and allies (Petunieae)

“…4D), a pattern observed in other empirical systems (e.g. (S. D. Smith and Rausher 2011;Hopkins and Rausher 2011;Sánchez-Cabrera et al 2021). The fact that only two red species in Petunieae appear to have evolved red flowers via shifts to less hydroxylated anthocyanins implicates other mechanisms for diversifying color.…”