Why do sunflowers have invisible colors?

Abstract

In the common sunflower, patterns of UV-absorbing pigments are controlled by a newly identified regulatory region and may be under the influence of environmental factors.

Keywords: abiotic stress; adaptation; evolutionary biology; floral pigmentation; genetics; genomics; plants; pollination; sunflower.

Figure 1.. Genetic factors controlling the size of UV-absorbing patterns in the common sunflower, and their relationship with environmental factors.

(A) To the human eye, sunflowers vary little in color, yet some parts of the flower (shown in purple) also absorb UV light (green lines) that we cannot see. These UV-absorbing regions vary in size due to differences in the distribution of flavonol pigments in modified petals called ligules. This creates a ‘bullseye’ pattern that varies in size. (B) Genome-wide association analysis (GWA) of parents and crosses of Helianthus annuus plants from various locations identified a locus (red circle) upstream of the HaMYB111 gene which underlies variation in UV absorbance; one allele is associated with large bullseyes (L, white) and the others with small ones (S, yellow). (C) The large bullseye allele is associated with increased expression of HaMYB111, which appears to increase the deposition of UV-absorbing flavonols in the ligules compared to the small allele. (D) Pollinators prefer sunflowers with intermediate UV absorbance – and medium bullseyes. (E) Smaller UV-absorbing regions and higher frequencies of the small UV-absorbing allele are found in populations from warmer and more humid climates (top right). The graph shows theoretical populations.