The Role of KANADI in Promoting Abaxial Cell Fates

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0234347BowmanLeaves of seed plants are formed from the flanks of apical meristems. Therefore, an inherent positional relationship exists between them: organ primordia have an adaxial side adjacent to the meristem, and an abaxial one away from the meristem. Surgical and genetic studies suggest that a morphogenetic gradient, whose source is the meristem, converts the inherent polarity into a functional one. Once an adaxial-abaxial axis of polarity is established within organ primordia, it provides cues for proper lamina growth and asymmetric development. Several key players involved in this process were identified recently, and analyses of these genes support and refine our views of axis formation in plants. Members of two gene families, the KANADIs and YABBYs, promote abaxial fates, and their expression is confined top the abaxial domains of developing lateral organs. When adaxial factors are active abaxially, the expression of the abaxial factors is eliminated, and vice versa. Thus, the adaxial and abaxial factors are expressed in mutually exclusive domains. The aim of this proposal is the characterization of the KANADIs, focusing on the role of the KANADIs in repressing adaxial factors, and the role of the KANADIs in promoting lamina expansion through the activity of the YABBYs. Experiments are proposed to address whether the interaction between the KANADIs and the adaxial factors and the YABBYs is direct or indirect and whether KANADI dependent lamina expansion is mediated via YABBY activity. Finally, experiments to integrate hypotheses based on classical meristem dissection experiments with genes identified via genetics are proposed. The basic research proposed should provide a foundation of knowledge to facilitate the modification of plant architecture. Since leaves provide the source of the majority of photosynthate, modification of their structure to maximize this process has the potential to increase agricultural productivity in many crop species.