Abstract

The sacred lotus (Nelumbo nucifera Gaertn.) can produce heat autonomously and maintain a relatively stable floral chamber temperature for several days when blooming. Floral thermogenesis is critical for flower organ development and reproductive success. However, the regulatory role of microRNA (miRNA) underlying floral thermogenesis in N. nucifera remains unclear. To comprehensively understand the miRNA regulatory mechanism of thermogenesis, we performed small RNA sequencing and transcriptome sequencing on receptacles from five different developmental stages. In the present study, a total of 172 known miRNAs belonging to 39 miRNA families and 126 novel miRNAs were identified. Twenty-nine thermogenesis-related miRNAs and 3024 thermogenesis-related mRNAs were screened based on their expression patterns. Of those, seventeen differentially expressed miRNAs (DEMs) and 1765 differentially expressed genes (DEGs) had higher expression during thermogenic stages. The upregulated genes in the thermogenic stages were mainly associated with mitochondrial function, oxidoreductase activity, and the energy metabolism process. Further analysis showed that miR156_2, miR395a_5, miR481d, and miR319p may play an important role in heat-producing activity by regulating cellular respiration-related genes. This study provides comprehensive miRNA and mRNA expression profile of receptacle during thermogenesis in N. nucifera, which advances our understanding on the regulation of floral thermogenesis mediated by miRNA.

Highlights

  • Several plant taxa can produce heat autonomously to ensure that the flower chamber temperature is higher than ambient temperatures

  • To visualize the phenomenon of floral thermogenesis in N. nucifera, flowers in the thermogenic stage grown in the natural environment were photographed with an infrared camera system FLIR-SC660 (FLIR SYSTEMS, USA) (Figure 1)

  • The 29 thermogenesis-related miRNAs and 3024 thermogenesis-related mRNAs were screened based on their differential expression between the thermogenic stages and the nonthermogenic stages

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Summary

Introduction

Several plant taxa can produce heat autonomously to ensure that the flower chamber temperature is higher than ambient temperatures. Previous research suggested that heat generation was associated with cyanide-resistant respiration mediated by an alternative oxidase (AOX) [7]. In addition to AOX, a plant uncoupling protein (UCP) located in the mitochondrial inner membrane is another energy dissipating system. Previous studies showed that the specific expression pattern of AOX and UCP seemed to depend on respiratory substrates. If the respiratory metabolic substrate was carbohydrate, the AOX gene was expressed; if the substrate was lipid, the UCP gene was expressed [14]. As these two energy-dissipation-related genes are expressed in nonthermogenic plants [15], there may be additional genes associated with floral thermogenesis. In the process of thermogenesis, the expression of some genes changed rapidly, which may be involved in epigenetic regulation [17]

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