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Why Flowers Look so Different: Scientists Make Progress in the Flexibility of Floral Structure and Its Underlying Mechanisms
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Flowers always show immense diversity in their phenotypes, including the arrangement of floral organs that can be whorled or spiral. In whorled flowers, the numbers of floral organs are usually fixed; in spiral flowers, in contrast, the numbers of floral organs usually show considerable variation, suggestive of the flexibility in the basic structure of the flower. The underlying mechanisms of the flexibility, however, remain unclear. Using Nigella damascena (Ranunculaceae) as a model, Prof. KONG Hongzhi’s research group at Institute of Botany, Chinese Academy of Sciences, attempted to address this question.

They found that the total number of floral organs per flower varies considerably within and between individuals. Interestingly, although all four types (i.e., sepals, petals, stamens, and carpels) of floral organs vary in number, stamen shows the widest range of variation and is the determining factor of the basic structure of the flower. They also showed that the total number of floral organs per flower is largely determined by 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 programs. By conducting extensive expression and functional studies, they further elucidated the genetic programs that specify the identities of different types of floral organs and the molecular mechanisms underlying their variation. They found that: 1) the expression patterns of most, if not all, floral organ identity genes are highly dynamic and show considerable variation between during flower development; 2) the dosage and duration of a gene required for the identity determination of one organ type may be different from that of another, so that a small change in the expression level of the gene may lead to alteration of the identity of the organ; 3) complex regulatory relationships exist among different floral organ identity genes, so that a change in one gene may cause chain reactions in others; and 4) some floral organ identity genes also regulate the boundaries between different types of floral organs.

These findings suggest that the floral organ identity determination programs are highly dynamic and show considerable flexibility. Transitions from spiral to whorled flowers, therefore, may be explained by evolution of the mechanisms that reduce the flexibility. These results provide new and important insights into the mechanisms underlying the flexibility and evolution of the flowers in structure.

This work was published in Nature Plants on December 7, 2015 (DOI: 10.1038/NPLANTS.2015.188). WANG Peipei, LIAO Hong and ZHANG Wengen (graduated) in Prof. KONG Hongzhi’s lab are the co-first authors of the paper. These works are supported by National Natural Science Foundation of China and the CAS Interdisciplinary Innovation Team projects. (Y约稿)

Figure: Phenotypes of VIGS-treated Nigella damascena flowers. For each treatment, only flowers with strong phenotypic changes are shown. Columns 1 and 2, top and side views of the flowers, respectively; columns 3, 4, 5 and 6, wild-type or homeotically transformed sepals, petals, stamens and carpels, respectively; and column 7, the mean numbers (boxes, with standard errors) of the different types of floral organs (for simplicity, only the 1st flowers are considered).


Article link: http://www.nature.com/articles/nplants2015188
Contact information
Prof. KONG Hongzhi
State Key Laboratory of Systematic and Evolutionary Botany
Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
E-mail: hzkong@ibcas.ac.cn

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