Dataset Information

Deciphering the complex leaf transcriptome of the allotetraploid species Nicotiana tabacum: a phylogenomic perspective.

ABSTRACT:

Background

Polyploidization is an important mechanism in plant evolution. By analyzing the leaf transcriptomes taken from the allotetraploid Nicotiana tabacum (tobacco) and parental genome donors, N. sylvesteris (S-Genome) and N. tomentosiformis (T-Genome), a phylogenomic approach was taken to map the fate of homeologous gene pairs in this plant.

Results

A comparison between the genes present in the leaf transcriptomes of N. tabacum and modern day representatives of its progenitor species demonstrated that only 33% of assembled transcripts could be distinguished based on their sequences. A large majority of the genes (83.6% of the non parent distinguishable and 87.2% of the phylogenetic topology analyzed clusters) expressed above background level (more than 5 reads) showed similar overall expression levels. Homeologous sequences could be identified for 968 gene clusters, and 90% (6% of all genes) of the set maintained expression of only one of the tobacco homeologs. When both homeologs were expressed, only 15% (0.5% of the total) showed evidence of differential expression, providing limited evidence of subfunctionalization. Comparing the rate of synonymous nucleotide substitution (Ks) and non-synonymous nucleotide substitution (Kn) provided limited evidence for positive selection during the evolution of tobacco since the polyploidization event took place.

Conclusions

Polyploidization is a powerful mechanism for plant speciation that can occur during one generation; however millions of generations may be necessary for duplicate genes to acquire a new function. Analysis of the tobacco leaf transcriptome reveals that polyploidization, even in a young tetraploid such as tobacco, can lead to complex changes in gene expression. Gene loss and gene silencing, or subfunctionalization may explain why both homeologs are not expressed by the associated genes. With Whole Genome Duplication (WGD) events, polyploid genomes usually maintain a high percentage of gene duplicates. The data provided little evidence of preferential maintenance of gene expression from either the T- or S-genome. Additionally there was little evidence of neofunctionalization in Nicotiana tabacum suggesting it occurs at a low frequency in young polyploidy.

SUBMITTER: Bombarely A

PROVIDER: S-EPMC3582432 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Publications

Deciphering the complex leaf transcriptome of the allotetraploid species Nicotiana tabacum: a phylogenomic perspective.

Bombarely Aureliano A Edwards Kieron D KD Sanchez-Tamburrino Juan J Mueller Lukas A LA

BMC genomics 20120817

<h4>Background</h4>Polyploidization is an important mechanism in plant evolution. By analyzing the leaf transcriptomes taken from the allotetraploid Nicotiana tabacum (tobacco) and parental genome donors, N. sylvesteris (S-Genome) and N. tomentosiformis (T-Genome), a phylogenomic approach was taken to map the fate of homeologous gene pairs in this plant.<h4>Results</h4>A comparison between the genes present in the leaf transcriptomes of N. tabacum and modern day representatives of its progenitor ...[more]

PMID: 22900718

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Project description:Pollen, an extremely reduced bicellular or tricellular male reproductive structure of flowering plants, serves as a model for numerous studies covering wide range of developmental and physiological processes. The pollen development represents a fragile and vital phase of plant ontogenesis and pollen was among the first singular plant tissues thoroughly characterized at the transcriptomic level (Honys and Twell [5]). Arabidopsis pollen developmental transcriptome has been published over a decade ago (Honys and Twell, 2004) and transcriptomes of developing pollen of other species have followed (Rice, Deveshwar et al. [2]; Triticeae, Tran et al. [11]; upland cotton, Ma et al. [8]). However, the transcriptomic data describing the development of tobacco pollen, a bicellular model for cell biology studies, have been missing. Here we provide the transcriptomic data covering three stages (Tupý et al., 1983) of wild type tobacco (Nicotiana tabacum, cv. Samsun) pollen development: uninucleate microspores (UNM, stage 1), early bicellular pollen (eBCP, stage 3) and late bicellular pollen (lBCP, stage 5) as a supplement to the mature pollen (MP), 4 h-pollen tube (PT4), 24 h-pollen tubes (PT24), leaf (LF) and root (RT) transcriptomic data presented in our previous studies (Hafidh et al., 2012a; Hafidh et al., 2012b). We characterized these transcriptomes to refine the knowledge base of male gametophyte-enriched genes as well as genes expressed preferentially at the individual stages of pollen development. Alongside updating the list of tissue-specific genes, we have investigated differentially expressed genes with respect to early expressed genes. Pollen tube growth and competition of pollen tubes in female pistil can be viewed as a race of the fittest. Accordingly, there is an apparent evolutionary trend among higher plants to store significant material reserves and nutrients during pollen maturation. This supply ensures that after pollen germination, the pollen tube utilizes its resource predominantly for its rapid elongation in the female pistil. Previous transcriptomic data from Arabidopsis showed massive expression of genes encoding proteins forming both ribosomal subunits that were accumulated in developing pollen, whereas their expression was not detectable in growing pollen tubes (Honys and Twell, 2004). We observed a similar phenomenon in less advanced bicellular tobacco pollen. Here, we describe in detail how we obtained and analyzed validated microarray dataset deposited in Gene Expression Omnibus (GSE62349).

Project description:BackgroundPollen tube growth is essential for plant reproduction and represents a widely employed model to investigate polarized cell expansion, a process important for plant morphogenesis and development. Cellular and regulatory mechanisms underlying pollen tube elongation are under intense investigation, which stands to greatly benefit from a comprehensive understanding of global gene expression profiles in pollen and pollen tubes. Here, RNA sequencing technology was applied to de novo assemble a Nicotiana tabacum male gametophytic transcriptome and to compare transcriptome profiles at two different stages of gametophyte development: mature pollen grains (MPG) and pollen tubes grown for six hours in vitro (PT6).ResultsDe novo assembly of data obtained by 454 sequencing of a normalized cDNA library representing tobacco pollen and pollen tube mRNA (pooled mRNA isolated from mature pollen grains [MPG] and from pollen tubes grown in vitro for 3 [PT3] or 6 [PT6] hours) resulted in the identification of 78,364 unigenes. Among these unigenes, which mapped to 24,933 entries in the Sol Genomics Network (SGN) N. tabacum unigene database, 24,672 were predicted to represent full length cDNAs. In addition, quantitative analyses of data obtained by Illumina sequencing of two separate non-normalized MPG and PT6 cDNA libraries showed that 8979 unigenes were differentially expressed (differentially expressed unigenes: DEGs) between these two developmental stages at a FDR q-value of <0.0001. Interestingly, whereas most of these DEGs were downregulated in PT6, the minor fraction of DEGs upregulated in PT6 was enriched for GO (gene ontology) functions in pollen tube growth or fertilization.ConclusionsA major output of our study is the development of two different high-quality databases representing the tobacco male gametophytic transcriptome and containing encompassing information about global changes in gene expression after pollen germination. Quantitative analyses of these databases 1) indicated that roughly 30% of all tobacco genes are expressed in the male gametophyte, and 2) support previous observations suggesting a global reduction of transcription after pollen germination. Interestingly, a small number of genes, many of which predicted to function in pollen tube growth or fertilization, were found to be upregulated in elongating pollen tubes despite globally reduced transcription.

Dataset Information

Deciphering the complex leaf transcriptome of the allotetraploid species Nicotiana tabacum: a phylogenomic perspective.

Background

Results

Conclusions

Publications

Deciphering the complex leaf transcriptome of the allotetraploid species Nicotiana tabacum: a phylogenomic perspective.

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