University of Oulu

Sandra Cervantes, Robert Kesälahti, Timo A Kumpula, Tiina M Mattila, Heikki Helanterä, Tanja Pyhäjärvi, Strong Purifying Selection in Haploid Tissue–Specific Genes of Scots Pine Supports the Masking Theory, Molecular Biology and Evolution, Volume 40, Issue 8, August 2023, msad183,

Strong purifying selection in haploid tissue-specific genes of Scots pine supports the masking theory

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Author: Cervantes, Sandra1,2; Kesälahti, Robert1; Kumpula, Timo A.2,3;
Organizations: 1Department of Ecology and Genetics, University of Oulu, Oulu, Finland
2Biocenter Oulu, University of Oulu, Oulu, Finland
3Laboratory of Cancer Genetics and Tumor Biology, Research Unit of Translational Medicine, University of Oulu, Oulu, Finland
4Human Evolution, Department of Organismal Biology, Uppsala University, Uppsala, Sweden
5Department of Forest Sciences, University of Helsinki, Helsinki, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.7 MB)
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Language: English
Published: Oxford University Press, 2023
Publish Date: 2023-10-24


The masking theory states that genes expressed in a haploid stage will be under more efficient selection. In contrast, selection will be less efficient in genes expressed in a diploid stage, where the fitness effects of recessive deleterious or beneficial mutations can be hidden from selection in heterozygous form. This difference can influence several evolutionary processes such as the maintenance of genetic variation, adaptation rate, and genetic load. Masking theory expectations have been confirmed in single-cell haploid and diploid organisms. However, in multicellular organisms, such as plants, the effects of haploid selection are not clear-cut. In plants, the great majority of studies indicating haploid selection have been carried out using male haploid tissues in angiosperms. Hence, evidence in these systems is confounded with the effects of sexual selection and intraspecific competition. Evidence from other plant groups is scarce, and results show no support for the masking theory. Here, we have used a gymnosperm Scots pine megagametophyte, a maternally derived seed haploid tissue, and four diploid tissues to test the strength of purifying selection on a set of genes with tissue-specific expression. By using targeted resequencing data of those genes, we obtained estimates of genetic diversity, the site frequency spectrum of 0-fold and 4-fold sites, and inferred the distribution of fitness effects of new mutations in haploid and diploid tissue–specific genes. Our results show that purifying selection is stronger for tissue-specific genes expressed in the haploid megagametophyte tissue and that this signal of strong selection is not an artifact driven by high expression levels.

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Series: Molecular biology and evolution
ISSN: 0737-4038
ISSN-E: 1537-1719
ISSN-L: 0737-4038
Volume: 40
Issue: 8
Article number: msad183
DOI: 10.1093/molbev/msad183
Type of Publication: A1 Journal article – refereed
Field of Science: 1181 Ecology, evolutionary biology
Funding: This work was supported by the Academy of Finland grants 287431, 293819, and 319313 to T.P., Biocenter Oulu (S.C.), and Emil Aaltonen Foundation (R.K.).
Academy of Finland Grant Number: 287431
Detailed Information: 287431 (Academy of Finland Funding decision)
293819 (Academy of Finland Funding decision)
319313 (Academy of Finland Funding decision)
Copyright information: © The Author(s) 2023. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.