From the notch signaling pathway to ribosome biogenesis

Nearly 240 WD repeat proteins have been identified from the Arabidopsis genome. Among these, some well characterized WDR proteins were shown to regulate various developmental processes in plants.1 We have recently isolated in Solanum chacoense a homolog of the Drosophila NOTCHLESS gene. In Drosophila, NOTCHLESS regulates the activity of the Notch signaling pathway through a direct interaction with the intracellular domain of the Notch receptor. Although the Notch signaling pathway does not exist in yease and plants, the NLE gene is conserved in animals, plants and yeast. Furthermore, functional conservation was suggested by expression of the plant NLE gene in Drosophila. In plants, underexpression of the plant NLE gene altered numerous developmental processes including seed development, and resulted in reduced aerial organ size and organ numbers, in delayed flowering, and in an increased stomatal index. Surprisingly, the link between these pleiotropic phenotypes is the recently discovered of the involvement of NLE in ribosome biogenesis, emphasizing its role in proper cellular growth and proliferation during plant development.