Molecular analysis of theLATERAL SUPPRESSORgene inArabidopsisreveals a conserved control mechanism for axillary meristem formation

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Abstract
In seed plants, shoot branching is initiated by the formation of new meristems in the axils of leaves, which subsequently develop into new axes of growth. This study describes the genetic control of axillary meristem formation by theLATERAL SUPPRESSOR(LAS) gene inArabidopsis thaliana. lasmutants show a novel phenotype that is characterized by the inability to form lateral shoots during vegetative development. The analysis shows that axillary meristem formation is differently regulated during different phases of development. During reproductive development, axillary meristems initiate in close proximity to the shoot apical meristem and do not requireLASfunction. In contrast, during the vegetative phase, axillary meristems initiate at a distance to the SAM and requireLASfunction. This control mechanism is conserved between the distantly related species tomato andArabidopsis. Monitoring the patterns ofLASandSHOOT MERISTEMLESStranscript accumulation allowed us to identify early steps in the development of leaf axil identity, which seem to be a prerequisite for axillary meristem initiation. Other regulators of shoot branching, likeREVOLUTAandAUXIN RESISTANT 1, act downstream ofLAS. The results are discussed in the context of the “detached meristem” and the “de novo formation” concepts of axillary meristem formation.