Abstract
Although biochemists and geneticists have studied the cotton flower for more than one century, little is known about the molecular mechanisms underlying the dramatic color change that occurs during its short developmental life following blooming. Through the analysis of world cotton germplasms, we found that all of the flowers underwent color changes post-anthesis, but there is a diverse array of petal colors among cotton species, with cream, yellow and red colors dominating the color scheme. Genetic and biochemical analyses indicated that both the original cream and red colors and the color changes post-anthesis were related to flavonoid content. The anthocyanin content and the expression of biosynthesis genes were both increased from blooming to one day post-anthesis (DPA) when the flower was withering and undergoing abscission. Our results indicated that the color changes and flavonoid biosynthesis of cotton flowers were precisely controlled and genetically regulated. In addition, flavonol synthase (FLS) genes involved in flavonol biosynthesis showed specific expression at 11 am when the flowers were fully opened. The anthocyanidin reductase (ANR) genes, which are responsible for proanthocyanidins biosynthesis, showed the highest expression at 6 pm on 0 DPA, when the flowers were withered. Light showed primary, moderate and little effects on flavonol, anthocyanin and proanthocyanidin biosynthesis, respectively. Flavonol biosynthesis was in response to light exposure, while anthocyanin biosynthesis was involved in flower color changes. Further expression analysis of flavonoid genes in flowers of wild type and a flavanone 3-hydroxylase (F3H) silenced line showed that the development of cotton flower color was controlled by a complex interaction between genes and light. These results present novel information regarding flavonoids metabolism and flower development.
Highlights
The diversity of flower color is one of the most beautiful gifts of nature, and it serves as a versatile tool for plant biochemists, geneticists and ecologists
3557 germplasms are from the Chinese Crop Germplasm Resources Information System (CGRIS) (Figure 1A), and the remaining 1107 germplasms are from the National Plant Germplasm System (GRIN) (Figure 1B)
14 types of colors are defined in CGRIS and 7 types are done in GRIN
Summary
The diversity of flower color is one of the most beautiful gifts of nature, and it serves as a versatile tool for plant biochemists, geneticists and ecologists. Different flower colors are constituted with various pigments and co-pigments. PH and ions play important roles in determining flower color [2,3,4]. In addition to endogenous genetic effects, environmental factors such as light and temperature could be responsible for the color of flowers [5,6,7,8]. In addition to its general phenotype, color confers flowers with diverse biological functions, such as protection against UV-light and the attraction of pollinators [9,10]. Multiple studies have indicated that, it is important for pollinator interaction, the mechanism of flower color changes pre- and post- anthesis is not well understood [13,14,15]
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