Transcriptome of Arabidopsis leaf senescence

Leaf senescence is a complex developmental process during which essential nutrients are recycled. In order to unravel the biochemical pathways and regulatory mechanisms that underlie this process, it would be valuable to examine the transcriptome associated with leaf senescence. Accordingly, an Arabidopsis thaliana leaf senescence cDNA library with approximately 10(4) recombinant clones was subjected to large-scale single-pass sequencing. Approximately 6200 expressed sequence tags (ESTs) were obtained, corresponding to 2491 unique genes. These included 134 genes encoding transcription factors and 182 genes whose products are components of signal transduction pathways, such as the mitogen-activated protein kinase (MAPK) cascades. A total of 116 of these genes are predicted to be involved in protein turnover, including 75 genes associated with the ubiquitin-proteasome pathway and 35 proteinases. Many of the genes are predicted to encode transporters for ions, amino acids and sugars, consistent with the substantial nutrient recycling during leaf senescence. In addition, this study revealed ESTs for 98 annotated genes for which ESTs did not previously exist and 46 novel transcribed units that have not previously been annotated in the Arabidopsis genome. Approximately one-third of the 2491 genes are predicted to encode proteins with unknown functions. The genes are distributed evenly on the five chromosomes.