Partners and Networks - Peptide Ligand-Receptor Signaling in Cell Separation Processes in Plants

Plants have the ability to produce new organs, like leaves, flowers and roots, continuously, and also loose organs throughout their life span - damaged and senesced leaves are shed, seeds and fruits abscise from the mother plant. These shedding events are controlled biological processes where cell walls between certain specialized cell layers (abscission zones) are broken down. We have identified the IDA gene that encodes a small peptide that functions as a signaling molecule and binds to receptors that trigger such cell separation events. In the model plant Arabidopsis thaliana this results in shedding of floral organs after pollination has taken place. we are investigating whether IDA and IDA-LIKE peptides and their receptors function also in other cell separation processes both in Arabidopsis and other species. All over the world farmers are suffering severe losses due to preharvest shedding of 5-20% of seeds or fruits. Research on cell separation processes is therefore of vital importance for future sustainable agriculture. We have now identified IDA and its receptors in all orders of flowering plants, from the most primitive, in monocots and dicots alike, and both in fruit and leaf abscission. Tests have shown that IDA and receptor genes from citrus and Brassica function like Arabidopsis own genes when transferred to Arabidopsis.

The assumed hegemonic role of classical plant hormones as governors of growth and development has lately been challenged by the discovery of peptides relaying communication between neighboring cells. For a few peptides, receptors have been identified. One signaling module is the small INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) interacting with the two closely related leucine-rich receptor-like kinases HAESA (HAE) and HAESA-LIKE2 (HSL2) to control floral organ loss in Arabidopsis. The same signaling modul e and similar cell wall remodeling enzymes are employed in cell separation during lateral root emergence. We will investigate transcription factor networks in these two processes to substantiate whether signaling pathways are reused in different cell sepa ration processes. Similar peptides may be involved in complex networks of ligand - receptor interactions. We have identified five IDA-LIKE (IDL) peptides, potentially interacting with HSL receptors, and partly functionally redundant to IDA. This, and pa rtly overlapping expression patterns at different sites of cell separation, argues for a common involvement of IDA and IDL peptides in such processes. One major aim of the project is to test whether hypothesized combinatorial function of IDA and IDL holds true, using genetic and biochemical approaches. Cell separation processes are crucial during the life cycle of all plants. We have identified IDA/IDL and HAE/HSL homologs in diverse species, and hypothesize that their function is conserved. Based on th e knowledge gained from Arabidopsis, we will unravel the regulation of cell separation processes in Brassica rapa. Premature shedding of leaves, flowers, fruitlets, fruits or seeds results in 5-20% reduction of yield in important crops and in quality loss in ornamentals (e.g. oilseed rape, soybean, alfalfa, grapevine, poinsettia). Thus, the genetic and molecular understanding of organ separation is important for competitive horticulture and sustainable agriculture