Genetic Regulation of the 2D to 3D Growth Transition in the Moss Physcomitrella patens - PubMed (original) (raw)

Genetic Regulation of the 2D to 3D Growth Transition in the Moss Physcomitrella patens

Laura A Moody et al. Curr Biol. 2018.

Abstract

One of the most important events in the history of life on earth was the colonization of land by plants; this transition coincided with and was most likely enabled by the evolution of 3-dimensional (3D) growth. Today, the diverse morphologies exhibited across the terrestrial biosphere arise from the differential regulation of 3D growth processes during development. In many plants, 3D growth is initiated during the first few divisions of the zygote, and therefore, the genetic basis cannot be dissected because mutants do not survive. However, in mosses, which are representatives of the earliest land plants, 3D shoot growth is preceded by a 2D filamentous phase that can be maintained indefinitely. Here, we used the moss Physcomitrella patens to identify genetic regulators of the 2D to 3D transition. Mutant screens yielded individuals that could only grow in 2D, and through an innovative strategy that combined somatic hybridization with bulk segregant analysis and genome sequencing, the causative mutation was identified in one of them. The NO GAMETOPHORES 1 (NOG1) gene, which encodes a ubiquitin-associated protein, is present only in land plant genomes. In mutants that lack PpNOG1 function, transcripts encoding 3D-promoting PpAPB transcription factors [1] are significantly reduced, and apical initial cells specified for 3D growth are not formed. PpNOG1 acts at the earliest identified stage of the 2D to 3D transition, possibly through degradation of proteins that suppress 3D growth. The acquisition of NOG1 function in land plants could thus have enabled the evolution and development of 3D morphology.

Keywords: developmental transitions; land plant evolution; morphogenesis; somatic hybridization.

Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

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Figures

Figure 1

Figure 1

3D Growth Is Abolished in Ppnog1-R Mutants (A–D) 7-day-old (A and C) and 1-month-old (B and D) wild-type (WT) (A and B) and Ppnog1-R (C and D) plants showing protonemal filaments (A and C) and the presence (WT, B) or absence (Ppnog1-R, D) of gametophores. (E) Mean number of gametophores/culture (n = 10) ± SEM (WT = 99.4 ± 5.62; Ppnog1-R = 0 ± 0; t test p < 0.05 ∗∗∗). Scale bars, 100 µm (A and C) and 1 mm (B and D). See Figure S1 for response to cytokinin and auxin.

Figure 2

Figure 2

Identification of the PpNOG1 Locus through Combined Somatic Hybridization and Bulk Segregant Analysis (A–C) Representative phenotype of 1-month-old wild-type Vx plant with gametophores (A), Ppnog1-R plant lacking gametophores (B), and Ppnog1-R/Gd hybrid exhibiting restored gametophore formation (C). Scale bars, 1 mm. (D) Phenotype of progeny derived from three independent Ppnog1-R/Gd hybrid sporophytes. Observed numbers are consistent with the hybrid gametophores being diploid, and the fertilized sporophytes being tetraploid. Chi-square test; p < 0.05 ∗∗∗. (E) Candidate genes in the genetic interval containing the _PpNOG1_ genetic locus. The C > T transition in gene 32970008 (red) generated a premature stop codon. See Figure S2 for overview of strategy.

Figure 3

Figure 3

A Premature Stop Codon in PpNOG1 Abolishes 3D Growth (A) PpNOG1 transcripts in parental Vx and Ppnog1-R. Blocks, exons; asterisks, in-frame stop codon. Scale bar, 1 kb. (B) PpNOG1 protein in Vx contains a ubiquitin-associated domain (UBA), which is missing in Ppnog1-R. # amino acid residues indicated. (C) Mean number of gametophores/culture (n = 10) in Vx, nog1-R, and five independent Ppnog1-R lines complemented with full-length PpNOG1 cDNA. Error bars ± SEM. (D–G) 1-month-old Vx (D), Ppnog1-R (E), complemented Ppnog1-R (F), Ppnog1-D1 (G), and Ppnog1-D2 (H) disruptant mutants. Scale bars, 1 mm. See Figure S3 and Data S1 for details of complementation and disruptant constructs.

Figure 4

Figure 4

PpNOG1 Function (A–L) Propidium iodide stained Vx (A–D) and Ppnog1-R (E–L) side-branch cells (A and E) and buds at 2- (B and F), 3- (C, G, and H), 4- (D, I, and J), and 5- (K and L) cell stages. Scale bars, 10 μm. , gametophore initial. (M–O) Relative transcript levels in protonemata: PpNOG1 in wild-type ± BAP and/or NAA (M) and PpAPB1-4 in Vx and the Ppnog1-D1 and the Ppnog1-D2 disruptants (N and O). ANOVA, ∗∗∗p < 0.05. (P and Q) Model for PpNOG1 function: PpDEK1 and PpNOG1 act antagonistically during side-branch initiation to regulate PpAPB transcription (P) and then act together to enable divisions that produce the gametophore initial (Q). See Figure S4 for NOG1 phylogeny.

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References

    1. Aoyama T., Hiwatashi Y., Shigyo M., Kofuji R., Kubo M., Ito M., Hasebe M. AP2-type transcription factors determine stem cell identity in the moss Physcomitrella patens. Development. 2012;139:3120–3129. - PubMed
    1. Cove D., Bezanilla M., Harries P., Quatrano R. Mosses as model systems for the study of metabolism and development. Annu. Rev. Plant Biol. 2006;57:497–520. - PubMed
    1. Harrison C.J., Roeder A.H., Meyerowitz E.M., Langdale J.A. Local cues and asymmetric cell divisions underpin body plan transitions in the moss Physcomitrella patens. Curr. Biol. 2009;19:461–471. - PubMed
    1. Kofuji R., Hasebe M. Eight types of stem cells in the life cycle of the moss Physcomitrella patens. Curr. Opin. Plant Biol. 2014;17:13–21. - PubMed
    1. Perroud P.-F., Cove D.J., Quatrano R.S., McDaniel S.F. An experimental method to facilitate the identification of hybrid sporophytes in the moss Physcomitrella patens using fluorescent tagged lines. New Phytol. 2011;191:301–306. - PMC - PubMed

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