The gene fimbriata interacts non-cell autonomously with floral regulatory genes

In Antirrhinum majus, one proposed role of the gene fimbriata (fim) is as a mediator between the floral meristem identify gene floricaula (flo) and fl oral organ identity genes such as deficiens (def) and plena (ple). The mech anism of firn activity is probably unique as, while the other genes in the hierarchy are thought to be transcription factors, firn is thought to targe t proteins to a ubiquitin-mediated destruction pathway. Both flo and def ha ve been shown to act non-cell autonomously. We tested the hypotheses that ( i) fim acts in a non-cell autonomous manner; and (ii) non-cell autonomy of flo might be through activation and subsequent non-cell autonomous activity of firn. Plants bearing an unstable fim allele were monitored for revertan t shoots. Analysis of firn RNA expression in plants derived from revertant shoots, and segregation of revertant phenotype in progeny from revertant pl ants, indicated that all were periclinal chimeras with wild-type fim expres sion only in subepidermal layers. Despite the absence of fim in the epiderm al layer, expression of downstream genes was normal, suggesting non-cell au tonomous activity of fim. Subsequently, we tested the hypothesis that firn is the mediator of flo non-cell autonomy by examining fim expression in flo periclinal chimeras. In these chimeras, firn is activated in cells where f lo is not expressed, indicating that firn cannot be the sole mediator of fl o non-cell autonomy.