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Summary: The ramosa2 mutant is visible in the ear and tassel. Mutant tassels do not have a sharp distinction between branches and spikelet pairs; rather, the long branches become shorter gradually toward the tip. Secondary branching occurs at a higher frequency. Often there are branches with spikelet pairs and single spikelets intermixed. Spikelet pair and spikelet pedicels are elongated, again becoming gradually less so toward the tip. In the ear, kernel rows may be uneven and branches may form, depending on allele and background. The phenotype is similar to ra1 and ra3, except ra2 mutants also have upright tassel branches. Expression levels of ra1 are decreased in ra2 mutants (Vollbrecht et al. 2005; Bortiri et al. 2006). The ra2 gene encodes a LOB (Lateral Organ Boundary) domain protein that is expressed transiently in branch meristems, spikelet pair meristems and spikelet meristems. A similar expression pattern is seen in other cereal species (Bortiri et al. 2006).
Image: ra2 ear and tassel
First and defining reports: Emerson et al. 1935, citing Brink. Bortiri et al 2006
Key Alleles
ra2-mum4 ARG to HIS.
ra2-DM deletion of LOB domain, leaving a C terminal conserved domain intact.
ra2-ref 8 bp insertion that introduces a stop codon in LOB domain.
References
Bortiri, E., Chuck, G., Vollbrecht, E., Rocheford, T.F., Martienssen, R., and Hake, S. (2006). ramosa2 encodes a Lateral Organ Boundary domain protein that determines the fate of stem cells in branch meristems of maize. The Plant Cell 18: 574-585. PUBMED
Emerson RA, Beadle GW, and Fraser AC (1935). A summary of linkage studies in maize. Cornell Univ. Agric. Exp. Sta. Mem. 180: 1-83.
Vollbrecht E, Springer PS, Goh L., Buckler ES and Martienssen R. (2005). Architecture of floral branch systems in maize and related grasses. Nature 436:1119-1126. PUBMED
Links: ra2 NCBI ra2 UniProt Q27YF3