AmGAI-like interacts with ROSINA, a putative transcriptional regulator of DEFICIENS in Antirrhinum majus

In Antirrhinum, development of petals and stamens in the second and third whorl is controlled by the homeotic B-function genes DEFICIENS and GLOBOSA, which belong to the MADS-box family of transcription factors. The encoded proteins form heterodimers and control petal and stamen organogenesis. A first step for a better understanding of the molecular control mechanisms was the isolation of ROSINA (RSI), a putative regulator of DEF, in a yeast one-hybrid screen using a DEF promoter fragment. RSI is a member of the b-ZIP family of transcription. Since such factors often need partners for exerting their regulatory function as heterodimers or multidimers, RSI was used as 'bait' in a yeast two-hybrid system to search for such potential partners. The most interesting candidate, named AmGAI-like, showed strong similarity to members of the GRAS family (GAI and RGA) of Arabidopsis. Expression of AmGAI-like revealed great similarity to the expression patterns of GAI and RGA of Arabidopsis. The protein-protein interaction between AmGAI-like and RSI was confirmed also biochemically by GST-pull down experiments.