A Comparison of Leaf and Petal Senescence in Wallflower Reveals Common and Distinct Patterns of Gene Expression and Physiology  

Abstract

Petals and leaves share common evolutionary origins but perform very different functions. However, few studies have compared leaf and petal senescence within the same species. Wallflower (Erysimum linifolium), an ornamental species closely related to Arabidopsis (Arabidopsis thaliana), provide a good species in which to study these processes. Physiological parameters were used to define stages of development and senescence in leaves and petals and to align these stages in the two organs. Treatment with silver thiosulfate confirmed that petal senescence in wallflower is ethylene dependent, and treatment with exogenous cytokinin and 6-methyl purine, an inhibitor of cytokinin oxidase, suggests a role for cytokinins in this process. Subtractive libraries were created, enriched for wallflower genes whose expression is up-regulated during leaf or petal senescence, and used to create a microarray, together with 91 senescence-related Arabidopsis probes. Several microarray hybridization classes were observed demonstrating similarities and differences in gene expression profiles of these two organs. Putative functions were ascribed to 170 sequenced DNA fragments from the libraries. Notable similarities between leaf and petal senescence include a large proportion of remobilization-related genes, such as the cysteine protease gene SENESCENCE-ASSOCIATED GENE12 that was up-regulated in both tissues with age. Interesting differences included the up-regulation of chitinase and glutathione S-transferase genes in senescing petals while their expression remained constant or fell with age in leaves. Semiquantitative reverse transcription-polymerase chain reaction of selected genes from the suppression subtractive hybridization libraries revealed more complex patterns of expression compared with the array data.

Production and Scavenging of Reactive Oxygen Species and Redox Signaling during Leaf and Flower Senescence: Similar But Different

“…expressed during senescence were in common between the two organs (Price et al, 2008;Wagstaff et al, 2009). Furthermore, cell death in both organs proceeds by a similar mechanism, which bears some similarities but also dissimilarities with classical autophagy, and has been termed vacuolar cell death (van Doorn et al, 2011).…”

Molecular cloning and characterization of a chitinase gene up-regulated in longan buds during flowering reversion

“…In addition, a wound-inducible class I acidic chitinase gene, win6, was reported in young undamaged poplar leaves, while a sharp increase, predominantly in pollen, coincided with anther dehiscence in flowers (Clarke et al, 1994). An unexpected abundance (23%) of chitinase genes was found in the libraries of senescing petals of wallflower (Erysimum linifolium) (Price et al, 2008). Evidently, abscission involves the dissolving of cell walls or cell separation, so that dehiscence and senescence are similar processes involving cell wall disruption through the action of chitinases (Roberts et al, 2002;Lewis et al, 2006).…”

Flower senescence: some molecular aspects

“…In Ipomoea, genes-In12, In15 and In21 have been found to encode products related to stress responses (Yamada et al 2007). Of the genes upregulated in wall flower petals specifically, 40 % have been found to encode chitinases, 23 % encode GSTs, 9 % are involved in reactive oxygen species (ROS)/stress responses, 9 % are involved in signaling, 6 % in remobilization/metabolism, 2 % in transcriptional regulation, 2 % in metal binding, and a further 9 % are of unknown function (Price et al 2008). Of the GST genes identified in wall flower, two genes have been found to be most similar to AtGSTF2 and AtGSTF3 from Arabidopsis.…”

“…Some of the genes have been found to be upregulated while others downregulated during flower senescence. The genes upregulated during normal developmental petal senescence relate to remobilization of nutrients, and include proteases, nucleases, lipases and transporters (Hong et al 2000;wagstaff et al 2002;Langston et al 2005;Price et al 2008). A general overview of some of the important genes or transcripts isolated from various flower systems is provided in Table 1.…”

“…In addition, microarray screens and analyses of individual genes have revealed that a number of genes, generally considered to be stressrelated, are also upregulated during petal senescence. These include metallothioneins, abscisic acid responsive genes and glutathione-S-transferases (Meyer et al 1991;Channelière et al 2002;Breeze et al 2004;Price et al 2008). In Ipomoea, genes-In12, In15 and In21 have been found to encode products related to stress responses (Yamada et al 2007).…”