Identifying Genes Involved in Pollination-induced Corolla Senescence in Petunia

The shelf life and marketability of ornamental plants can be increased by delaying flower senescence.  While many genes that are differentially expressed during flower senescence have been identified, we still do not have a detailed understanding of the pathways that are involved in the initiation of corolla senescence.  We created strand-specific, paired-end RNA-sequencing libraries from corollas of pollinated and unpollinated Petunia × hybrida flowers at 12, 18, and 24 hours, in order to identify genes that are regulating pollination-induced flower senescence.  Nearly 0.5 billion reads were sequenced using Illumina HiSeq technology.  De novo assembly after pre-processing generated more than 161K contigs, which were paired down to a 33K unigene library. Over two thousand differentially expressed contigs were identified in pollinated corollas using the statistical package DESeq2.  Weighted gene correlation network analysis was used to assign contigs into modules based on expression patterns. Three pollination-specific modules were identified from this analysis. One module (red) had increased expression across all pollinated corollas in all times points. The other two modules (cyan and grey) had a peak of gene expression in pollinated corollas 18 hours after pollination. A total of nine unique, enriched KEGG pathways were identified, many of which are directly involved in metabolic processes. In the red module, four enriched KEGG pathways were identified, including plant-pathogen interaction. Many of these genes are calcium and calmodulin-related genes often involved in cell signalling. The grey module was enriched for five KEGG pathways including the regulation of autophagy and ubiquitin mediated proteolysis. The cyan module had two enriched KEGG pathways, glycerolipid metabolism and endocytosis. These data show that gene changes occur in the corolla within 12 hours after pollination, and that senescence is induced well before fertilization. The identification of enriched KEGGs allows for a more directed selection of genes for future characterization.  The goal of this research is to identify the best targets for manipulating flower senescence and improving shelf life.