Sex is determined by XY chromosomes across the radiation of dioeciousNepenthespitcher plants

Abstract

Species with separate sexes (dioecy) are a minority among flowering plants, but dioecy has evolved multiple times independently in their history. The sex‐determination system and sex‐linked genomic regions are currently identified in a limited number of dioecious plants only. Here, we study the sex‐determination system in a genus of dioecious plants that lack heteromorphic sex chromosomes and are not amenable to controlled breeding: Nepenthes pitcher plants. We genotyped wild populations of flowering males and females of three Nepenthes taxa using ddRAD‐seq and sequenced a male inflorescence transcriptome. We developed a statistical tool (privacy rarefaction) to distinguish true sex specificity from stochastic noise in read coverage of sequencing data from wild populations and identified male‐specific loci and XY‐patterned single nucleotide polymorphsims (SNPs) in all three Nepenthes taxa, suggesting the presence of homomorphic XY sex chromosomes. The male‐specific region of the Y chromosome showed little conservation among the three taxa, except for the essential pollen development gene DYT1 that was confirmed as male specific by PCR in additional Nepenthes taxa. Hence, dioecy and part of the male‐specific region of the Nepenthes Y‐chromosomes likely have a single evolutionary origin.

The Diversity and Dynamics of Sex Determination in Dioecious Plants

“…Sex determination has also been investigated in Nepenthes pitcher plants ( Scharmann et al, 2019 ). The species of this genus are all dioecious and carnivorous.…”

Sex‐chrom, a database on plant sex chromosomes

“…Another efficient approach, particularly useful in nonmodel organisms, is SEX-DETector (Muyle et al, 2016), a probabilistic method that using RNAseq high-throughput sequencing of parental species and their progeny can infer autosomal and sex-linked genes. More recently, a double digest RADseq (ddRADseq) has been used to address sex determination across the radiation of dioecious Nepenthes (Scharmann et al, 2019).…”

Nepenthes × ventrata Transcriptome Profiling Reveals a Similarity Between the Evolutionary Origins of Carnivorous Traps and Floral Organs

“…To verify the presence of the MADS-box transcripts in nonflowering N. × ventrata tissues (developing pitcher), we searched available transcriptome data on N. × ventrata late pitcher (24 h after opening) (Wan Zakaria et al, 2016) (NCBI TSA: Nepenthes ventricosa × Nepenthes alata, transcriptome shotgun assembly; GFAD00000000.1) and male inflorescence of another relative species N. khasiana (Scharmann et al, 2019). As a result, we found homologs of AGL24, AGL42, SVP, SOC1, FUL, AP1, SEP1, SEP2, SEP3, SEP4, AG, STK, AP3, AGL6, AGL14, AGL16, AGL19, AGL37, AGL61, AGL66, AGL80, and AGL104 genes in the N. × ventrata pitcher transcriptome, which confirms the reliability of the data obtained in this study.…”

“…Carnivorous plants, including Nepenthes spp., use insects both as pollinators and as food, participating in pollinatorprey conflict (Jürgens et al, 2012). Nepenthes pitchers, which do not or weakly reflect UV radiation visible to insects (Schaefer and Ruxton, 2008), acquire the same red color in pitchers and flower tepals by increasing anthocyanin production (Scharmann et al, 2019).…”

“…Besides traps, dioecious Nepenthes species form female and male flowers on separate plants and, therefore, must have a complete set of highly conserved MADS-box genes associated with flowering (Subramanyam and Narayana, 1971). Indeed, the N. khasiana male inflorescence transcriptome (Scharmann et al, 2019) contained the similar set of the MADS-box genes as N. × ventrata leaves and pitchers (Supplementary Tables 2, 12).…”