Coordination of proximal-distal and adaxial-abaxial patterning during early ovule development of Arabidopsis thaliana

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Sexual reproduction is a salient aspect of plants. Within the flower of angiosperms the gynoecium carries one or multiple ovules, the major female reproductive organs. The ovule harbors the egg cell, it is the site where fertilization occurs and the embryo develops during seed formation. Apart from their exciting biology, the ovules of the model plant Arabidopsis thaliana have gained attraction as a prominent model system to study organogenesis. A major question relates to the molecular basis of pattern formation in the early ovule primordium. In previous research we identified a number of genes with a role in early ovule development. Our genetic evidence suggests that NOZZLE (NZZ), encoding a putative transcription factor, coordinates proximaldistal and adaxia-abaxial (anterior-posterior) pattern formation in the early ovule by negatively regulating the INNER NO OUTER (INO) autoregulatory feedback loop. INO is a member of the YABBY family, which is implied in the regulation of abaxial identity in lateral organs, and affects outer integument development. The idea is that precocious activation of INO eventually results in aberrant P-D pattern formation. Thus, differentiation along the adaxial-abaxial axis in the chalaza may not begin before development along the P-D axis has proceeded to a certain extent. We also obtained in vitro data indicating that the NZZ and at least some YABBY proteins, including INO, interact directly. The first goal of this proposal is to test if the NZZ-INO interaction occurs in vivo using biochemical, in vivo imaging and molecular-genetic approaches. The second line of experiments aims at a better understanding of the molecular basis of this interaction and assesses the generality of the NZZ-YABBY protein interactions. The third goal consists in the molecular characterisation of a new genetic factor involved in early outer integument development.