Content area
Full Text
RESEARCH ARTICLE
Plant architecture is dictated by morphogenetic factors that specify the number and symmetry of lateral organs as well as their positions relative to the primary axis. Mutants defective in the patterning of leaves and floral organs have provided new insights on the signaling pathways involved, but there is comparatively little information regarding aspects of the patterning of stems, which play a dominant role in architecture. To this end, we have characterized five alleles of the brevipedicellus mutant of Arabidopsis, which exhibits reduced internode and pedicel lengths, bends at nodes, and downward-oriented flowers and siliques. Bends in stems correlate with a loss of chlorenchyma tissue at the node adjacent to lateral organs and in the abaxial regions of pedicels. A stripe of achlorophyllous tissue extends basipetally from each node and is positioned over the vasculature that services the corresponding lateral organ. Map-based cloning and complementation studies revealed that a null mutation in the KNAT1 homeobox gene is responsible for these pleiotropic phenotypes. Our observation that wild-type Arabidopsis plants also downregulate chlorenchyma development adjacent to lateral organs leads us to propose that KNAT1 and ERECTA are required to restrict the action of an asymmetrically localized, vasculature-associated chlorenchyma repressor at the nodes. Our data indicate that it is feasible to alter the architecture of ornamental and crop plants by manipulating these genetically defined pathways.
INTRODUCTION
The generation of asymmetries is an underlying theme in the development of higher eukaryotes. Organismal complexity arises progressively through the deposition and interpretation of positional information that refines and elaborates previously established spatial and temporal patterns. In plants, shoot and inflorescence development can be visualized as a reiterative process generating successively greater numbers of leaves, axillary meristems, and stems. The establishment and maintenance of this pattern requires the action of molecular switches that respond to positional information and mediate sharp transitions between different types of tissue and cellular identities. Loss of patterning factors in mutants can result in the transformation of cellular and tissue identities of one region to those characteristic of other locations, thus producing morphological novelties (Bowman, 2000; Ng and Yanofsky, 2001).
In higher plants, the formation of aerial organs is dependent on the activity of the shoot apical meristem (SAM), a dome-shaped morphogenetic field in which...