Genetic basis and dual adaptive role of floral pigmentation in sunflowers

Abstract

Variation in floral displays, both between and within species, has been long known to be shaped by the mutualistic interactions that plants establish with their pollinators. However, increasing evidence suggests that abiotic selection pressures influence floral diversity as well. Here, we analyse the genetic and environmental factors that underlie patterns of floral pigmentation in wild sunflowers. While sunflower inflorescences appear invariably yellow to the human eye, they display extreme diversity for patterns of ultraviolet pigmentation, which are visible to most pollinators. We show that this diversity is largely controlled by cis-regulatory variation affecting a single MYB transcription factor, HaMYB111, through accumulation of ultraviolet (UV)-absorbing flavonol glycosides in ligules (the ‘petals’ of sunflower inflorescences). Different patterns of ultraviolet pigments in flowers are strongly correlated with pollinator preferences. Furthermore, variation for floral ultraviolet patterns is associated with environmental variables, especially relative humidity, across populations of wild sunflowers. Ligules with larger ultraviolet patterns, which are found in drier environments, show increased resistance to desiccation, suggesting a role in reducing water loss. The dual role of floral UV patterns in pollinator attraction and abiotic response reveals the complex adaptive balance underlying the evolution of floral traits.

Evolution and functional diversification of R2R3-MYB transcription factors in plants

“…Moreover, different types of flavonoid regulation are broadly observed. For instance, regulatory roles have been reported for PhMYB15 and PpMYBF1 in flavonol biosynthesis in peach fruit [ 197 ], FhMYB21L2 in flavonol biosynthesis in Freesia [ 109 ], CsPH4 in proanthocyanidin biosynthesis in citrus [ 198 ], SlMYB72 in carotenoid biosynthesis in tomato [ 199 ], CaMYB108 in capsaicinoid biosynthesis in pepper [ 200 ], AgMYB1 in apigenin biosynthesis in celery [ 137 ], HaMYB111 in floral ultraviolet patterning in sunflower [ 201 ], and SmMYB2 in phenolic acid biosynthesis in Salvia miltiorrhiza [ 202 ]. Apart from model flowers such as Petunia and Antirrhinum , a number of flowering bulbs have also been studied recently, including Freesia [ 203 , 204 ], Cattleya [ 205 ], and Narcissus [ 206 ].…”

Flower orientation influences floral temperature, pollinator visits and plant fitness

“…Domesticated sunflower ( Helianthus annuus L.) provides an excellent Asteraceae model for studying the process of anthesis due to the ample genomic resources available and because their large capitula contain thousands of individual florets that undergo anthesis over several days (Putt, 1940; Stuessy et al ., 1986; Sun & Ganders, 1990; Andersson, 2008; Badouin et al ., 2017; Terzić et al ., 2017). A major adaptation for pollinator attraction in sunflowers is the development of ray florets, the elongated, flattened corollas of the outer sterile whorl that are brightly coloured and often have UV nectar guides (Wojtaszek & Maier, 2014; Terzić et al ., 2017; Todesco et al ., 2021). The inner disc florets are fertile flowers, which are developmentally distinct from one another.…”

Characterization and differentiation of pollen lipidomes and proteomes from different intrafloral stamens in heterantherous Senna bicapsularis

“…UV patterns can increase floral visibility and significantly influence pollinator visitation and preference (Todesco et al . 2022). The results suggest that pollinator orientation is probably not achieved by anther pigment in S. bicapsularis .…”