Morphological novelties, including formation of trait combinations, may result from de novo gene origination and/or co-option of existing genes into other developmental contexts. A variety of shape-color combinations of capitular florets occur in Chrysanthemum and its allies. We hypothesized that co-option of a carotenoid cleavage dioxygenase gene into the floral symmetry gene network would generate a white zygomorphic ray floret.We tested this hypothesis in an evolutionary context using species in Chrysanthemum sensu lato, a monophyletic group with diverse floral shape-color combinations, based on morphological investigation, interspecific crossing, molecular interaction and transgenic experiments.Our results showed that white color was significantly associated with floret zygomorphy. Specific expression of the carotenoid cleavage dioxygenase gene CCD4a in marginal florets resulted in white color. Crossing experiments between Chrysanthemum lavandulifolium and Ajania pacifica indicated that expression of CCD4a is trans-regulated. The floral symmetry regulator CYC2g can activate expression of CCD4a with a dependence on TEOSINTE BRANCHED1/ CYCLOIDEA/PROLIFERATING (TCP) binding element 8 on the CCD4a promoter.Based on all experimental findings, we propose that gene co-option of carotenoid degradation into floral symmetry regulation, and the subsequent dysfunction or loss of either CYC2g or CCD4a, may have led to evolution of capitular shape-color patterning in Chrysanthemum sensu lato.
A new species from the Qinghai-Tibetan Plateau is described and illustrated. Rhodiola yushuensis S.Y. Meng et J. Zhang sp. nov. is similar to Rhodiola smithii (Hamet) S. H. Fu, but it differs in its inner caudex leaves with obvious petioles and the leaf blades are obovate-triangular (vs. inner caudex leaves with strongly descends to the base of the petiole, and the leaves are long linear) and the outer caudex leaves are scalelike, triangular-suborbicular (vs. scalelike, narrowly triangular). Principal component analysis (PCA) analysis of the leaf traits and seed coat architecture also showed that R. yushuensis can be separated from R. smithii. The nrDNA internal transcribed spacer (ITS) sequences also support the claim that this plant is a new species, and it is grouped with R. smithii.
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