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Revelation of ancestral roles of KNOX genes by a functional analysis of Physcomitrella homologues

  • Cell Biology and Morphogenesis
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Abstract

KNOX genes are indispensable elements of indeterminate apical growth programmes of vascular plant sporophytes. Since little is known about the roles of such genes in non-vascular plants, functional analysis of moss KNOX homologues (MKN genes) was undertaken using the genetically amenable model plant, Physcomitrella patens. Three MKN genes were inactivated by targeted gene knockout to produce single, double and triple mutants. MKN2 (a class 1 KNOX gene) mutants were characterised by premature sporogenesis, abnormal sporophyte ontogeny and irregular spore development. MKN4 (a second class 1 gene) mutants were phenotypically normal. MKN1-3 (a class 2 KNOX gene) mutants exhibited defects in spore coat morphology. Analysis of double and triple mutants revealed that the abnormal sporophytic phenotype of MKN2 mutants was accentuated by mutating MKN4 and to a lesser degree by mutating MKN1-3. The aberrant spore phenotype of MKN1-3 and MKN2 mutants was exacerbated by mutating MKN4. This study provides the first instance in which an abnormal phenotype has been associated with the disruption of a class 2 KNOX gene as well as the first demonstrated case of functional redundancy between a class 1 and a class 2 KNOX gene. We conclude that KNOX genes play significant roles in programming sporophytic development in moss and we provide evidence that ancestral function(s) of this gene family were instrumental in the successful transition of plants to a terrestrial environment.

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Abbreviations

DIG:

Digoxigenin

gDNA:

Genomic deoxyribonucleic acid

GUS:

β-Glucuronidase

HPT:

Hygromycin phosphotransferase

NPT:

Neomycin phosphotransferase

paba:

p-Aminobenzoic acid

RAGE:

Rapid amplification of genomic ends

SAM:

Shoot apical meristem

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Acknowledgments

This study was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) operating grant awarded to N.W. Ashton and NSERC postgraduate scholarships provided to S.D. Singer (PGSA & B). We wish to thank W. Chapco for invaluable advice concerning statistical analysis and E. Barker for searching the genomes of Physcomitrella patens, Chlamydomonas reinhardtii, Ostreococcus lucimarinus and Ostreococcus tauri.

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  1. Department of Biology, University of Regina, Regina, SK, Canada, S4S 0A2

    S. D. Singer & N. W. Ashton

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  1. S. D. Singer
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  2. N. W. Ashton
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Correspondence to N. W. Ashton.

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Communicated by R. Reski.

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Singer, S.D., Ashton, N.W. Revelation of ancestral roles of KNOX genes by a functional analysis of Physcomitrella homologues. Plant Cell Rep 26, 2039–2054 (2007). https://doi.org/10.1007/s00299-007-0409-5

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