[Show abstract][Hide abstract] ABSTRACT: An analysis of changes in global gene expression patterns during developmental leaf senescence in Arabidopsis has identified more than 800 genes that show a reproducible increase in transcript abundance. This extensive change illustrates the dramatic alterations in cell metabolism that underpin the developmental transition from a photosynthetically active leaf to a senescing organ which functions as a source of mobilizable nutrients. Comparison of changes in gene expression patterns during natural leaf senescence with those identified, when senescence is artificially induced in leaves induced to senesce by darkness or during sucrose starvation-induced senescence in cell suspension cultures, has shown not only similarities but also considerable differences. The data suggest that alternative pathways for essential metabolic processes such as nitrogen mobilization are used in different senescent systems. Gene expression patterns in the senescent cell suspension cultures are more similar to those for dark-induced senescence and this may be a consequence of sugar starvation in both tissues. Gene expression analysis in senescing leaves of plant lines defective in signalling pathways involving salicylic acid (SA), jasmonic acid (JA) and ethylene has shown that these three pathways are all required for expression of many genes during developmental senescence. The JA/ethylene pathways also appear to operate in regulating gene expression in dark-induced and cell suspension senescence whereas the SA pathway is not involved. The importance of the SA pathway in the senescence process is illustrated by the discovery that developmental leaf senescence, but not dark-induced senescence, is delayed in plants defective in the SA pathway.
The Plant Journal 06/2005; 42(4):567-85. DOI:10.1111/j.1365-313X.2005.02399.x · 6.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Programmed cell death (PCD) is an active cellular suicide that occurs in animals and plants throughout development and in response to both abiotic and biotic stresses. In contrast to animals, little is known about the molecular machinery that regulates plant PCD. We have previously identified transcriptomic changes associated with heat- and senescence-induced PCD in an Arabidopsis cell suspension culture [Plant J. 30 (2002) 431]. However, since plant PCD is also likely to involve elements that are regulated post-transcriptionally, we have undertaken a proteomic analysis in the Arabidopsis system. We identified 11 proteins that increased in abundance relative to total protein in both treatments despite extensive degradation of other proteins. We argue that some of these proteins are maintained during PCD and may therefore have specific functions in the PCD pathway. The increased abundance of several antioxidant proteins as well as a measured increase in free Fe2+ content of the cells indicates an oxidative stress in this system. Several mitochondrial proteins were identified, confirming the importance of this organelle during PCD. We also identified an extracellular glycoprotein that may function in the transmission of a 'death signal' from cell to cell. Putative roles for the identified proteins are presented.
[Show abstract][Hide abstract] ABSTRACT: Programmed cell death (PCD) is a form of cellular suicide requiring active gene expression, and occurs in both animals and plants. While the cascade of events and the genes that control PCD have been extensively studied in animals, we remain largely ignorant about the similar process in plant cells. Many of the key proteins of animal cell death such as the Bcl-2 family and the caspase family of proteases do not appear to be conserved in plants, suggesting that plants may employ unique mechanisms to execute PCD. To identify genetic elements of PCD in plants, we monitored changes in transcript levels of approximately 100 selected genes during cell death in an Arabidopsis cell suspension culture using a cDNA microarray. PCD was induced in the cell cultures by two independent means (heat treatment or by allowing the cultures to senesce) to allow the distinction to be drawn between changes in gene expression that are related to PCD and those that are specific to a particular treatment. We argue that genes whose expression is altered during PCD induced by two different means may be generally involved in all types of PCD. We show that certain oxidative stress-related genes, including CSD1, CSD3, and GPX, in addition to cysteine proteinases, some transcription factors, and HR-related genes may serve as markers of a core plant cell death programme. Additionally we observe a down-regulation of the mitochondrial adenine nucleotide transporter and suggest that this may be an early event in the execution of plant PCD.
The Plant Journal 06/2002; 30(4):431-46. DOI:10.1046/j.1365-313X.2002.01301.x · 6.82 Impact Factor