Table 1.

Major functional categories of senescence-associated genes*

Functional category	Associated processes	Abundant genes
Macromolecule degradation	Breakdown of proteins, nucleic acids, lipids and polysaccharides	Cysteine proteases, ubiquitin-related genes, RING finger proteins, nucleases, lipases/acylhydrolases, phospholipases, glucanases, β-glucosidase, pectinesterases, and polygalacturonase
Nutrient recycling	Transport of peptides, amino acids, sugars, purines, pyrimidines and ions	Oligopeptide transporters, ammonium transporter purine and pyrimidine transporters, glutamine synthetase and glutamate synthase, sugar transporters (MFSs), and ABC transporters
Defense and cell rescue mechanisms	Abiotic and biotic stress, and oxidative stress	Metallothionein, glutathione S-transferase, protein similar to jasmonate-inducible protein, glutathione peroxidase, and cold-regulated protein COR6.6
Transcriptional regulation	Transcription factors	Zinc finger proteins, basic helix-loop-helix proteins, bZIP proteins, HMG-box proteins and transcription factors of the WRKY, NAC, AP2, MYB, HB, TCP and GRAS families
Signal transduction	Protein phosphorylation and dephosphorylation	Receptor-like kinases, components of MAP kinase signal cascades, phosphatases and phospholipases, calcium-binding EF-hand protein RD20, calcium-dependent protein kinases, and cytoskeleton-associated proteins

*Determined by the abundance of senescence-associated ESTs, as described by Guo et al. [4]. bZIP, basic leucine zipper; HB, homeobox protein; HMG, high mobility group; MAP, mitogen-activated kinase; MSF, major facilitator superfamily; NAC, no apical meristem (NAM) proteins.