Abstract
Rafflesia, a holoparasitic genus that produces the largest flower in the world is characterized by the absence of leaves, stem and other macroscopic organs. To better understand the molecular regulation of flower development in this genus we isolated and characterized a floral MADS-box gene, namely, RcMADS1 from Rafflesia cantleyi. Heterologous expression analysis in Arabidopsis was chosen because Rafflesia is not amenable to genetic manipulations. RcMADS1 shares sequence similarity with AGAMOUS-LIKE 24 (AGL24) and SHORT VEGETATIVE PHASE (SVP) of Arabidopsis. Ectopic expression of RcMADS1 in Arabidopsis caused early flowering and conversion of sepals and petals into leaf-like structures, and carpels into inflorescences. In 35S::RcMADS1 plants SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), a downstream target gene of AGL24, was upregulated. 35S::RcMADS1 plants exhibit early flowering and conversion of the floral meristem into inflorescence meristem, as in 35S::AGL24 plants. Similar to AGL24, RcMADS1 could rescue the late flowering phenotypes of agl24-1 and FRIGIDA, but not the early flowering of svp-41. Based on these results, we propose that RcMADS1 is a functional ortholog of Arabidopsis AGL24.
Highlights
Rafflesia is a parasitic plant in a distinctive flowering plant genus from Rafflesiaceae that develops the largest flower in the world [1]
We succeeded in cloning a MADS-box gene by reversetranscription PCR using degenerate primers with cDNA synthesized from Rafflesia cantleyi floral buds
Results from a tblastx search using the online Basic Local Alignment Search Tool (BLAST) program revealed high sequence similarities to MADS-box proteins such as PtMADS1 from Populus tomentosa, JOINTLESS from Solanum lycopersicum, MPF2 from Physalis pubescens, MPP3 from Physalis peruviana, IbMADS4 from
Summary
Rafflesia is a parasitic plant in a distinctive flowering plant genus from Rafflesiaceae that develops the largest flower in the world [1]. The members of this genus are unique among the flowering plants owing to their highly reduced vegetative morphology, prominent and large floral structures, and physiology. Rafflesia species are holoparasitic endophytes of Tetrastigma (Vitaceae) They lack visible leaves, stems and roots and only appear as flowers for sexual reproduction [2]. Their vegetative body is reduced to mycelium-like structure, which grows completely embedded within the host plants. Rafflesia flowers have some unusual structures, such as a modified perianth (perigone) enclosed by a diaphragm; a central column with an apical disk; and the presence of ramenta on the interior surface of the perigone tube and diaphragm (Figure S1) [3]
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