title: Flexibility in the structure of spiral flowers and its underlying mechanisms.
abstract: Spiral flowers usually bear a variable number of organs, suggestive of the flexibility in structure. The mechanisms underlying the flexibility, however, remain unclear. Here we show that in Nigella damascena, a species with spiral flowers, different types of floral organs show different ranges of variation in number. We also show that the total number of organs per flower is largely dependent on the initial size of the floral meristem, whereas the respective numbers of different types of floral organs are determined by the functional domains of corresponding genetic programmes. By conducting extensive expression and functional studies, we further elucidate the genetic programmes that specify the identities of different types of floral organs. Notably, the AGL6-lineage member NdAGL6, rather than the AP1-lineage members NdFL1/2, is an A-function gene, whereas petaloidy of sepals is not controlled by AP3- or PI-lineage members. Moreover, owing to the formation of a regulatory network, some floral organ identity genes also regulate the boundaries between different types of floral organs. On the basis of these results, we propose that the floral organ identity determination programme is highly dynamic and shows considerable flexibility. Transitions from spiral to whorled flowers, therefore, may be explained by evolution of the mechanisms that reduce the flexibility.
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Peipei
authors.initials: P
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Liao
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Wengen
authors.initials: W
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xianxian
authors.initials: X
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Shan
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xiaoshan
authors.initials: X
authors.lastname: Duan
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Yao
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Hongzhi
authors.identifier: http://orcid.org/0000-0002-0034-0510
authors.initials: H
authors.lastname: Kong
mesh_terms: D035264:Flowers / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D031861:Nigella damascena / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics
chemical_list: D010940:Plant Proteins