NOZZLE regulates proximal-distal pattern formation, cell proliferation andearly sporogenesis during ovule development in Arabidopsis thaliana

With the characterisation of the NOZZLE gene we aim at a better understandi ng of the molecular and genetic mechanism underlying pattern formation and growth control during floral organogenesis, Our data indicate that NOZZLE l inks these processes during ovule development. In the ovule primordium NOZZ LE plays a central role in the formation of the nucellus through antagonizi ng the activities of BELL, AINTEGUMENTA and INNER NO OUTER, all encoding pu tative transcription factors, in the prospective nucellar region. We provid e evidence that NOZZLE and BELL are chalaza identity genes that share overl apping functions in establishing the prospective chalaza of the ovule. In a ddition, NOZZLE plays a role in controlling the cell number and by this mea ns the length of the funiculus, again through antagonizing AINTEGUMENTA and INNER NO OUTER function. NOZZLE is also required for the development of th e integuments. We show that during the initial phase of this process NOZZLE is transcriptionally regulated by AINTEGUMENTA and INNER NO OUTER. NOZZLE thus represents a downstream target of these two genes in the integument de velopment pathway.