Spontaneous mutations in KNOX genes give rise to a novel floral structure in Antirrhinum.
BACKGROUND
Petal spurs-tubular outgrowths that collect nectar-are considered key innovations because of their ability to change pollinator specificity and so cause reproductive isolation and speciation. Spurs have arisen frequently and rapidly in many taxa. To test their potential origins, we isolated spontaneous dominant mutations at two loci, HIRZ and INA, that cause novel outgrowths from Antirrhinum petals, resembling the petal spurs of closely related genera.


RESULTS
HIRZ and INA were isolated and shown to encode similar KNOX homeodomain proteins that are normally expressed only in apical meristems and are likely to act redundantly. Both dominant mutations were caused by transposon insertions in noncoding regions that caused ectopic expression of functional transcripts, either in petals or in all lateral organs with more pleiotropic effects. Formation of a spur-like outgrowth, which resembled an ectopic petal tube, was dependent both on KNOX gene expression and dorsiventral asymmetry of the flower.


CONCLUSIONS
These mutations provide an example of how petal spurs might evolve rapidly due to changes in regulatory gene expression.
Golz
John F
JF
Institute of Cell and Molecular Biology, University of Edinburgh, King's Buildings, Mayfield Road, EH9 3JR, Edinburgh, United Kingdom.
Keck
Emma J
EJ
Hudson
Andrew
A
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D004251:DNA Transposable Elements; D018398:Homeodomain Proteins / Q000235:genetics* / Q000502:physiology*; D018519:Meristem; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D063245:Plant Development; D018515:Plant Leaves / Q000254:growth & development; D010940:Plant Proteins; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D004251:DNA Transposable Elements; D018398:Homeodomain Proteins; C405985:Knox1 protein, plant; D010940:Plant Proteins; C097496:STM protein, Arabidopsis