Abstract
Eucommia ulmoides is a model representative of the dioecious plants with sex differentiation at initiation. Nevertheless, the genetic mechanisms of sexual dimorphism and sex determination in E. ulmoides remain poorly understood. In this study de novo transcriptome sequencing on Illumina platform generated >45 billion high-quality bases from fresh leaves of six male and female individuals of E. ulmoides. A total of 148,595 unigenes with an average length of 801 base-pairs (bp) were assembled. Through comparative transcriptome analyses, 116 differentially expressed genes (DEGs) between the males and the females were detected, including 73 male-biased genes and 43 female-biased genes. Of these DEGs, three female-biased genes were annotated to be related with the sexually dimorphic gutta content in E. ulmoides. One male-biased DEG was identified as putative MADS box gene APETALA3, a B class floral organ identity gene in the flowering plants. SNPs calling analyses further confirmed that the APETALA3-like gene was probably involved in the sex determination in E. ulmoides. Four other male-biased DEGs were potential sex-associated genes as well with segregated SNPs in accord with sex type. In addition, the SNPs density was 1.02 per kilobase (kb) in the expressed genes of E. ulmoides, implying a relatively high genetic diversity.
Highlights
Eucommia ulmoides Oliver is a dioecious tree species of the family Eucommiaceae, in the asterid lineage of the angiosperms [1], that is endemic to southern and central China [2]
A total of six individuals of E. ulmoides from three independent full-sib families with each sex having three individuals were sequenced according to Illumina PE sequencing protocol
About eight to ten gig abases (Gb) raw sequencing data were generated for each individual, reaching to a total of 327,129,846 raw reads in all the samples
Summary
Eucommia ulmoides Oliver is a dioecious tree species of the family Eucommiaceae, in the asterid lineage of the angiosperms [1], that is endemic to southern and central China [2]. It is a Tertiary relict species that has been a well-known medicinal plant in China for >2000 years [3]. E. ulmoides has the potential to replace the commonly known para-rubber tree (Hevea brasiliensis from the Euphorbiaceae, which only grows in tropical zones) because of its wide distribution in the subtropical and temperate ecozones and good resistance [7,8]. Sex-identification of the young seedlings of E. ulmoides is difficult due to its dioecious sexual system and long-life cycle, which constrains its breeding process [9]. The yields of gutta in the leaves differ significantly between male and female E. ulmoides trees [10], making it essential to identify the sex-associated genes for molecular sex-typing of E. ulmoides to assist the breeding progress for improving the yield of gutta or other target traits
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