| The mechanism of floral development is a hot point in plant developmental biology. The molecular mechanism of floral organ development is accounted by ABCE-model, a well-established model that assumes floral organ identity is determined by four classes of homeotic genes, namely are A-, B-, C-, and E-class genes. The A-and E-class genes complex develops sepals; the A-, B-, and E-class genes combine to regulate petal formation; the B-, C-, and E-class genes together control stamen identity; and the class C and E genes combine to regulate carpel identity. This model is applicable to a large number of dicotyledonous species, but for the monocots with the vestigial and abnormal floral organs, the genetic mechanism of floral development is still unclear. Zingiberaceae exhibit a specialized floral design. Besides sepals, petals, stamens, and carpels, this plant group also retains the petaloid lateral staminodes and labellum staminodes which differ significantly among species. Numerous researches have shown that the specialized floral organs play a key role in reproductive success during interaction with pollinators. However, the molecular mechanism of these specialized floral organs is poorly studied. Two ginger species with strikingly different lateral staminodes each other, H. flavum and A. mutica, were selected to explore how the ABCE-class genes determine the diversity of floral morphology.(1). The partial sequences of the floral development genes HfFUL, H/AP3, HfPI, and HfAG of H. flavum have been obtained by applying degeneracy primers and 3’RACE. The partial sequences of the floral identity genes (AmFUL, AmAP3, AmPI-1, AmPI-2, AmAG, and AmSEP3) of A. mutica were obtained from the transcriptome data. A phylogenetic analysis was carried out on amino acid sequences of these genes and also on other selected homologous genes of monocotylous and dicotylous species.(2). Our experiment involves a highly sensitive and specific measurement that assess the variation of expression of these genes in development stages and floral organs with the aid of qRT-PCR and in situ hybridization. The results of in situ hybridization showed, at flower development early stage, expression patterns of H/AP3 and AmAP3 were similar; HfPI, AmPI-1 and AmPI-2 also displayed similar expression pattern as well, but unlike the other two genes, HfPI was detected to express in ovules. qRT-PCR results showed A-class, B-class, and C-class genes of A. mutica and H. flavum had similar expression pattern in different floral organs at flower development later stage.(3). To investigate the potential functions of AmFUL in floral organ identity and development, the cDNA driven by the CaMV35S promoter was transformed into Arabidopsis plants. Compared with wild type plants,35S::AmFUL transgenic plants showed early flowering, and the short and weak plants. One of the transgenic plants produced a flower in the position of the sepal, another transgenic plant produced a flower with three carpels. These phenotypes are similar with the most of APl/FUL-like genes from other monocots.Our results indicate:(1) The formation of the petaloid floral organ in Zingiberaceae is primarily related to the B class genes. (2) In both species, A-, B-, and C-class genes display similar expression pattern in labellum staminodes and stamens, this result strongly supports the hypothesis that the labellum of Zingiberaceae originates from stamens. (3) AmFUL gene may have an ancestrally conservative function in promoting flowering and carpel formation, even in regulating sepal and petal identity. |
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