De novo transcriptome of the mayfly Cloeon viridulum and transcriptional signatures of Prometabola.

Qin Si,Wei Zhang,Juan-Yan Luo,Chang-Fa Zhou,Ze Hu,Peng Xu

doi:10.1371/journal.pone.0179083

Abstract

Mayflies (Ephemeroptera) display many primitive characters and a unique type of metamorphosis (Prometabola). However, information on the genomes and transcriptomes of this insect group is limited. The RNA sequencing study presented here generated the first de novo transcriptome assembly of Cloeon viridulum (Ephemeroptera: Baetidae), and compared gene expression signatures among the young larva (YL), mature larva (ML), subimago (SI), and imago (IM) stages of this mayfly. The transcriptome, based on 88 Gb of sequence data, comprised a set of 81,185 high quality transcripts. The number of differentially expressed genes (DEGs) in YL vs. ML, ML vs. SI, and SI vs. IM, was 4,825, 1,584, and 1,278, respectively, according to the reads per kilobase of transcript per million mapped reads analysis, assuming a false discovery rate <0.05 and a fold change >2. Gene enrichment analysis revealed that these DEGs were enriched in the “chitin metabolic process”, “germ cell development”, “steroid hormone biosynthesis”, and “cutin, suberine, and wax biosynthesis” pathways. Finally, the expression pattern of a selected group of candidate signature genes for Prometabola, including vestigial, methoprene-tolerant, wingless, and broad-complex were confirmed by quantitative real time-PCR analysis. The Q-PCR analysis of larval, subimaginal, and imaginal stages of C. viridulum suggests that the development of mayflies more closely resembles hemimetamorphosis than holometamorphosis.

Highlights

(Ephemeroptera) fossil records have more than 300 million years
The hierarchical clustering of 100 differentially expressed genes (DEGs), based on the log2 [reads per kilobase of transcript per million mapped reads (RPKM) + 1] of 12 samples showed that these genes could be divided into five clusters, most with uniquely expressed genes; genes in cluster III were expressed in both young larva (YL) and SI samples. These results revealed that differences in gene expression during C. viridulum development were remarkable and that the selected samples could be sorted into four distinct groups based on different stages (Fig 4), which was evidenced in the Venn diagram produced for the distribution of different genes between each pair of stages (p-value cut off of 0.05, Fig 2D)
The present study provided a de novo transcriptome of the mayfly C. viridulum based on its four developing stages: young larva, mature larva, subimago, and imago

Summary

Introduction

The living species show many primitive and unique characteristics of winged insects, including a four-stage (Prometabola) life history (egg, larva, subimago, and imago), unfolded wings, obvious corrugation on wings, long segmented tails, and nymphs with paired gills. Among these characteristics, the prometabolan pattern with two winged instars (subimago and imago) is the most primitive metamorphosis found in Pterygota and it exists exclusively in Ephemeroptera. The origin of Prometabola and functions of subimagos have been extensively discussed [1]. The key questions concerning the role of the subimago and subimagos change in Prometabola.

Methods

Results

Discussion

Conclusion