Abstract
Rafflesia is a unique plant species existing as a single flower and produces the largest flower in the world. While Rafflesia buds take up to 21 months to develop, its flowers bloom and wither within about a week. In this study, transcriptome analysis was carried out to shed light on the molecular mechanism of senescence in Rafflesia. A total of 53.3 million high quality reads were obtained from two Rafflesia cantleyi flower developmental stages and assembled to generate 64,152 unigenes. Analysis of this dataset showed that 5,166 unigenes were differentially expressed, in which 1,073 unigenes were identified as genes involved in flower senescence. Results revealed that as the flowers progress to senescence, more genes related to flower senescence were significantly over-represented compared to those related to plant growth and development. Senescence of the R. cantleyi flower activates senescence-associated genes in the transcription activity (members of the transcription factor families MYB, bHLH, NAC, and WRKY), nutrient remobilization (autophagy-related protein and transporter genes), and redox regulation (CATALASE). Most of the senescence-related genes were found to be differentially regulated, perhaps for the fine-tuning of various responses in the senescing R. cantleyi flower. Additionally, pathway analysis showed the activation of genes such as ETHYLENE RECEPTOR, ETHYLENE-INSENSITIVE 2, ETHYLENE-INSENSITIVE 3, and ETHYLENE-RESPONSIVE TRANSCRIPTION FACTOR, indicating the possible involvement of the ethylene hormone response pathway in the regulation of R. cantleyi senescence. Our results provide a model of the molecular mechanism underlying R. cantleyi flower senescence, and contribute essential information towards further understanding the biology of the Rafflesiaceae family.
Highlights
Rafflesia is a unique plant species existing as a single flower and produces the largest flower in the world
BLASTX search resulted in a total of 39,234 (61%) and 26,775 (42%) unigenes matched to NCBI non-redundant (NR) and Swiss-Prot sequences, respectively
The similarity search performed on the unigenes against the Leaf Senescence Database (LSD 2.0) successfully identified 13,679 (21.3%) unigenes with significant matches to senescence-associated protein sequences (Supplementary Dataset S1)
Summary
Rafflesia is a unique plant species existing as a single flower and produces the largest flower in the world. A total of 53.3 million high quality reads were obtained from two Rafflesia cantleyi flower developmental stages and assembled to generate 64,152 unigenes Analysis of this dataset showed that 5,166 unigenes were differentially expressed, in which 1,073 unigenes were identified as genes involved in flower senescence. Senescence is the last developmental stage of a plant’s life cycle, which involves highly coordinated structural, biochemical, and molecular changes that lead to the death of organs and the whole plant[12]. Studies of flower senescence at the molecular level have revealed genes involved in various cellular activities, including protein degradation (e.g., PRT22 in Sandersonia; RbCP1 in Rosa), nutrient remobilization (e.g., pDcCP1 in Dianthus; DAFSAG2 in Narcissus), and nucleic acid degradation (e.g., DSA6 in Hemerocallis; PhNUC1 in Petunia; DcNUC1 in Dianthus)[15,16,17]. This is more so as the plant exists almost entirely as a single flower, and as such, senescence of the single organ correlates directly with plant death
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