PATTERN-FORMATION AND GROWTH DURING FLORAL ORGANOGENESIS - HUELLENLOSAND AINTEGUMENTA ARE REQUIRED FOR THE FORMATION OF THE PROXIMAL REGION OF THE OVULE PRIMORDIUM IN ARABIDOPSIS-THALIANA

Our understanding of the molecular mechanisms that regulate and integr ate the temporal and spatial control of cell proliferation during orga n ontogenesis, particularly of floral organs, continues to be primitiv e. The ovule, the progenitor of the seed, of Arabidopsis thaliana has been used to develop an effective model system for the analysis of pla nt organogenesis. A typical feature of a generalized ovule is the line ar arrangement of at least three distinct elements, the funiculus, cha laza and nucellus, along a proximal-distal axis, This pattern is suppo sed to be established during the early proliferative phase of ovule de velopment, We provide genetic evidence that the young ovule primordium indeed is a composite structure. Two genes, HUELLENLOS and AINTEGUMEN TA have overlapping functions in the ovule and differentially control the formation of the central and proximal elements of the primordium. The results indicate that proximal-distal pattern formation in the Ara bidopsis ovule takes place in a sequential fashion, starting from the distal end. Furthermore, we show that HUELLENLOS also regulates the in itiation and/or maintenance of integument and embryo sac ontogenesis a nd interestingly prevents inappropriate cell death in the young ovule.