Dissection and comparison of cell separation processes in plants

Plants are provided with cell separation mechanisms whereby entire organs become detached from the plant body when they have served their purpose. However natural, premature abscission of leaves, flowers, fruitlets, fruits or seeds results in quality loss in ornamentals and significant reduction of yield (5-20%) in important crops all over the world (e.g. oilseed rape, soybean, alfalfa, grapevine, poinsettia). Thus the molecular understanding of the physiological process that leads to organ separation is important for competitive horticulture and sustainable agriculture. We are using the model plant Arabidopsis thaliana to investigate these mechanisms and have identified genes controlling such processes. The major results in this project is the detailed characterization of the peptide IDA, a small molecule involved in cell-to-cell communication by binding certain receptors (HAE/HSL2) where cell separation is taking place. Mutation in the genes encoding IDA or HAE/HSL2 results in a deficiency of floral organ abscission. We have furthermore discovered that this signaling module is active at other sites of cell separation, i.e. the plant is reusing the molecular mechanisms in different settings. Our latest achievement has been to show the same genes controlling floral organ abscission in Arabidopsis is also responsible for abscission of flowers and fruits in citrus species. Accumulating evidence from our group and other researchers indicate that IDA is involved in cell separation in a number of flowering plants.

Plants are provided with cell separation mechanisms whereby entire organs become detached from the plant body when they have served their purpose. However natural, premature abscission of leaves, flowers, fruitlets, fruits or seeds results in quality loss in ornamentals and significant reduction of yield (5-20%) in important crops all over the world (e.g. oilseed rape, soybean, alfalfa, grapevine, poinsettia). Thus the molecular understanding of the physiological process that leads to organ separation is important for competitive horticulture and sustainable agriculture. Floral organ abscission in Arabidopsis thaliana serves as a model for cell separation processes where cell wall material between adjacent cells is broken down. The small peptide INFLORES CENCE DEFICIENT IN ABSCISSION (IDA) that signals through the closely related leucine-rich receptor-like kinases (LRR-RLKs) HAESA (HAE) and HAESA-LIKE2 (HLS2), controls the separation of sepals, petals and stamens after pollination has taken place. Our wor king hypothesis is that similar signaling pathways as well as similar cell wall remodeling enzymes are used in other cell separation processes both in Arabidopsis and other plants species. The major aim of the proposed project is to test whether this hyp othesis holds true by comparing floral organ abscission to other cell separation events. To this end we find it necessary to deepen our understanding of the IDA/HAE HSL2 signaling system, to identify more components of this pathway and to explore the sugg ested functional redundancy of IDA-LIKE (IDL) and HAESA-LIKE (HSL) genes found in Arabidopsis and in other species. Thus, this project promises to extend our understanding of important cell separation processes in plants, to identify novel receptor-ligan d pairs involved in plant development, and to provide knowledge for future translational applications in crops and ornamentals.