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Title: RAMOSA2 ENCODES A LATERAL ORGAN BOUNDARY DOMAIN PROTEIN THAT DETERMINES THE FATE OF STEM CELLS IN BRANCH MERISTEMS OF MAIZE

Author
item BORTIRI, ESTEBAN - ARS-UCB PLNT GENE EXP CTR
item Chuck, George
item VOLLBRECHT, ERIK - GDCB IOWA STATE AMES IA
item ROCHEFORD, TORBERET - UNIV ILLINOIS URBANA IL
item MARTIENSSEN, ROB - COLD SPRING HARBOR LAB NY
item Hake, Sarah

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2005
Publication Date: 3/1/2006
Citation: Bortiri, E., Chuck, G.S., Vollbrecht, E., Rocheford, T., Martienssen, R., Hake, S.C. 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.

Interpretive Summary: Genetic control of grass inflorescence architecture is critical given that cereal seeds provide most of the world's food. Seeds are borne on axillary branches, which arise from groups of stem cells in axils of leaves and whose branching patterns dictate most of the variation in plant form. Normal maize (Zea mays) ears are unbranched, and tassels have long branches only at their base. The ramosa2 (ra2) mutant of maize has increased branching with short branches replaced by long, indeterminate ones. The ra2 gene was cloned based on its genetic location and shown to encode a transcription factor that is expressed early in axillary branch development. The gene and its expression pattern are conserved across the grasses, suggesting it may play an important role in these other species.

Technical Abstract: Genetic control of grass inflorescence architecture is critical given that cereal seeds provide most of the world's food. Seeds are borne on axillary branches, which arise from groups of stem cells in axils of leaves and whose branching patterns dictate most of the variation in plant form. Normal maize (Zea mays) ears are unbranched, and tassels have long branches only at their base. The ramosa2 (ra2) mutant of maize has increased branching with short branches replaced by long, indeterminate ones. ra2 was cloned by chromosome walking and shown to encode a LATERAL ORGAN BOUNDARY domain transcription factor. ra2 is transiently expressed in a group of cells that predicts the position of axillary meristem formation in inflorescences. Expression in different mutant backgrounds places ra2 upstream of other genes that regulate branch formation. The early expression of ra2 suggests that it functions in the patterning of stem cells in axillary meristems. Alignment of ra2-like sequences reveals a grass-specific domain in the C terminus that is not found in Arabidopsis thaliana. The ra2-dm allele suggests this domain is required for transcriptional activation of ra1. The ra2 expression pattern is conserved in rice (Oryza sativa), barley (Hordeum vulgare), sorghum (Sorghum bicolor), and maize, suggesting that ra2 is critical for shaping the initial steps of grass inflorescence architecture.