Arabidopsis shoot organogenesis is enhanced by an amino acid change in the ATHB15 transcription factor

The hoc mutant displays high organogenic competence for in vitro shoot regeneration without addition of exogenous phytohormones. The genetic basis of this phenotype is investigated here. Using genetic mapping, the HOC locus was identified on chromosome 1. A point mutation was found in the At1g52150 gene, which encodes ATHB15/CORONA/INCURVATA4, a class III HD-ZIP transcription factor. The mutation replaced a serine with a cysteine in the MEKHLA domain of the protein. The wild-type ATHB15 gene was able to complement the hoc phenotype. Organogenesis response experiments revealed that hoc organogenic capacity was affected by the genetic background, and that it was not caused by a loss of ATHB15 function but by an effect of the mutation on protein function.