The present invention is situated in the field of plant development. More specifically the invention relates to the identification and characterization of plant development regulating proteins (cdc27B) required for correct plant development as well as to mutants (hbt, HOBBIT) thereof. The present invention thus relates to isolated nucleic acid sequences and protein sequences, and to vectors and host cells comprising said nucleic acid sequences. The invention further relates to transgenic cells and plants comprising and expressing said sequences and to methods for obtaining said cells and plants. The present invention further relates to the use of said wild type or mutant genes and proteins in methods to modify plant development. Said genes and proteins can furthermore be used in methods for mimicking or modifying auxin-related effects.