Characterization of the Ra1 maize gene involved in inflorescence architecture

The genetic and molecular control of inflorescence and flower development has been extensively studied in model dicotyledonous plants such as Arabidopsis but even now little is known about monocotyledonous species. In maize several mutants have been isolated that perturbed normal inflorescence development. In particular, the Ramosa1 (Ra1) gene, coding for a zinc finger transcription factor, plays a role in inflorescence structure by determining the number of branches. Although the mechanism by which Ra1 acts is unclear, inflorescence meristems in these regions assume a branch meristem identity rather than becoming spikelet pairs. In this work we characterize a new mutation of Ra1 gene that originated spontaneously from a B73 inbred line. This loss-of-function mutation is caused by the deletion of the lysine residue at position 53 in the RA1 putative zinc-finger domain. This is the first evidence for a single amino acid deletion in the zinc finger domain that knocks out the function of the RA1 protein. This result strongly suggests that the RA1 protein functions by acting as a DNA-binding protein, probably involved in transcriptional regulation. Furthermore, Ra1 overexpression in the Arabidopsis ortholog superman (sup) mutant, whose flowers are characterized by the presence of additional stamens, was not able to restore the correct stamen number, indicating that SUP and Ra1 genes do not share an identical function.