Gene expression in opening and senescing petals of morning glory (Ipomoea nil) flowers

Abstract

We isolated several senescence-associated genes (SAGs) from the petals of morning glory (Ipomoea nil) flowers, with the aim of furthering our understanding of programmed cell death. Samples were taken from the closed bud stage to advanced visible senescence. Actinomycin D, an inhibitor of transcription, if given prior to 4 h after opening, suppressed the onset of visible senescence, which occurred at about 9 h after flower opening. The isolated genes all showed upregulation. Two cell-wall related genes were upregulated early, one encoding an extensin and one a caffeoyl-CoA-3-O-methyltransferase, involved in lignin production. A pectinacetylesterase was upregulated after flower opening and might be involved in cell-wall degradation. Some identified genes showed high homology with published SAGs possibly involved in remobilisation processes: an alcohol dehydrogenase and three cysteine proteases. One transcript encoded a leucine-rich repeat receptor protein kinase, putatively involved in signal transduction. Another transcript encoded a 14-3-3 protein, also a protein kinase. Two genes have apparently not been associated previously with senescence: the first encoded a putative SEC14, which is required for Golgi vesicle transport, the second was a putative ataxin-2, which has been related to RNA metabolism. Induction of the latter has been shown to result in cell death in yeast, due to defects in actin filament formation. The possible roles of these genes in programmed cell death are discussed.

Flower senescence: some molecular aspects

“…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). 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).…”

“…BoSPT1 (603 bp) has been reported to encode a predicted protein of 121 amino acids while BoSPT2 (573 bp) encodes a predicted protein of 103 amino acids. Yamada et al (2007) isolated several senescence-associated genes (SAGs) from the petals of morning glory (Ipomoea nil) flowers. Two cell wall-related genes, one encoding an extensin (plant structural cell wall proteins implicated in growth and in disease resistance response) and one a caffeoyl-CoA-3-O-methyl transferase (involved in lignin production) have been found to be upregulated during early floral development while as a pectin acetyl asterase (implicated to be involved in cell wall degradation) has been found to be upregulated after flower opening.…”

“…Senescence involves a highly regulated gene expression and the presence of concerted mechanisms of cellular degradation (Yamada et al 2007). The processes of senescence and senescence-induced PCD are regulated by a coordinated signaling pathway, which is consistent with the view that senescence involves PCD (Coupe et al 2004).…”

Autophagy regulates progression of programmed cell death during petal senescence in Japanese morning glory

“…[2][3][4] Japanese morning glory (Ipomoea nil) has ephemeral flowers that open in the morning and generally show visible petal senescence symptoms within 12 hours after flower opening. We previously showed that treatment with cycloheximide and actinomycin D, which inhibit protein and RNA synthesis, respectively, dramatically delays petal senescence, and also that DNA degradation and chromatin condensation occur during petals senesce in Japanese morning glory, 5,6 indicating that petal senescence of this plant is regulated by PCD.…”

“…5 In a recent functional study, 7 we produced transgenic plants with reduced expression of PSRs. Transgenic plants with reduced InPSR26 expression (PRS26r lines) showed accelerated visible petal senescence.…”