Analysis of the immediate wound response in plants

Hertha Firnberg Position T 93 Analysis of the Immediate Wound Response in Plants Claudia JONAK 27.06.2000 Wounding belongs to the most severe environmental stresses plants have to cope with and can be caused by mechanical injury, herbivore or pathogen attack. Wound responses include reversible protein phosphorylation, synthesis of the plant hormone jasmonic acid (JA), transcriptional activation of different sets of genes and metabolic adaptation to count for the increased energy demand. Recently, I have provided evidence that two novel protein kinases, WAG (wound-activated glycogen synthase kinase-3) and WIG (wound-induced glycogen synthase kinase-3), from alfalfa might be involved in mediating the local, immediate wound response. I intend to investigate the role of WAG and WIG in the local, early wound signal transduction. A genetic approach is proposed to analyse (I) whether WAG and/or WIG kinases regulate wound-induced JA accumulation, (II) whether p50WAG and/or p53WIG action are necessary for wound-induced gene expression and (III) whether MAP kinases and WAG and WIG kinases act on the same or on different pathways. Additionally, I propose to characterize putative interaction partners of WAG and WIG which have been isolated by a yeast two-hybrid screen. These clones indicate that WAG and WIG might regulate gone expression by modulating transcription factor activities and might link signal transduction to wound-induced metabolic adaptation.

Plants continuously encounter various stresses that hamper growth and development or even challenge their survival. Wounding belongs to the most severe environmental stress and can be caused by mechanical injury, herbivore or pathogen attack. As sessile organisms plants have developed sophisticated mechanisms to cope with these threats. In order to react, plants have to recognize the signal first. Subsequently, the signal is communicated within the cell and throughout the plant. This process is called signal transduction and ultimately leads to an appropriate physiological response. Protein kinases are major elements in signal transduction pathways. Protein kinases are enzymes that phosphorylate and thereby alter the properties of target proteins. Within the framework of this project a specific class of plant protein kinases, the glycogen synthase kinase 3/shaggy-like kinases (GSKs), were studied. Biochemical experiments revealed that WIG (wound-induced GSK) is activated when leaves are wounded. We could show that WIG kinase activity is low in healthy leaves, but is rapidly and transiently induced upon injury. Thus activation of WIG belongs to the immediate early response to mechanical damage. During the research project we analysed whether GSKs are involved in other plant stress responses, too. We exposed roots to various environmental stresses and analysed GSK activity. We found that the activity of MsK4 is low in roots under normal growth conditions. However, high salinity treatment of the roots rapidly induced MsK4 activity indicating that MsK4 might be involved in high salt signal transduction. Intensified irrigation and fertilization have resulted in high soil salinity becoming an increasingly deleterious obstacle to growth and yield of crop plants in many areas of the word. Thus detailed knowledge on high salt signal transduction is of great significance. We analysed the impact of MsK4 action on the hyperosmotic stress response further and generated plants constitutively overexpressing MsK4. Subsequent high salt tolerance tests showed that plants overexpressing MsK4 were more resistant to high salinity stress than control plants. The localization of a signaling component within the cell is essential for its cellular function. Investigation of the subcellular location of MsK4 revealed that MsK4 localizes to plastids that contain starch. Starch is a polymer of glucose and of primary importance as an energy and carbon store. Starch metabolism in plants is highly sensitive to changes in the environment. Salt stress leads to carbon mobilization from starch, suggesting that MsK4 might function to adjust carbohydrate metabolism to environmental stress conditions. We are presently investigating this hypotesis.