Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2012
Publication Date: 4/15/2013
Citation: Foley, M.E., Chao, W.S., Horvath, D.P., Dogramaci, M., Anderson, J.V. 2013. The transcriptomes of dormant leafy spurge seeds under alternating temperature are differentially affected by a germination-enhancing pretreatment. Journal of Plant Physiology. 170(6):539-547.
Interpretive Summary: Leafy spurge is a noxious perennial weed. We are investigating seed dormancy and germination to increase our knowledge aimed at biologically-based management for this species. Leafy spurge requires alternating- rather than constant-temperature for germination. Thus, we examined the effect of alternating temperature on global patterns of gene expression in seeds imbibed for 21 days and upon germination using the transcriptome of seeds imbibed for 3 days as the baseline. As might be expected, the prolonged imbibition resulted in overrepresentation of pathways associated with plant defense while germination highlighted pathways associated with metabolism and signaling of plant hormones.
Technical Abstract: Seed dormancy is an important stage in the life cycle of many non-domesticated plants, often characterized by the temporary failure to germinate under conditions that normally favor the process. Pre-treating dormant imbibed seeds at a constant temperate accelerated germination of leafy spurge seeds under alternating temperatures. However, dormant seeds will also germinate without a pre-treatment, albeit at a much slower rate, which gives rise to longer periods of imbibition before germination. Transcriptome analyses on seeds exposed to prolonged imbibition highlighted pathways associated with phenylpropanoid biosynthesis and interacting networks of genes involved in plant defense. In addition to the many pathways associated with phenylpropanoid biosynthesis enriched with down-regulated genes upon germination, there were also numerous pathways enriched with up-regulated genes associated with energy metabolism, such as glycolysis. Transcriptome data further suggest that metabolism and signaling by the plant hormones ethylene, gibberellin, and abscisic acid are involved in the developmental transition from dormancy to germination. More specifically, sub-network enrichment analysis identified ABI3 as a central hub of a sub-network at germination including several down-regulated genes such as DELLA (i.e., RGL2), which represses gibberellin signaling processes required for germination. The 595-fold increase in the expression of ACC oxidase (ACO4) at germination also suggests an important a role for ethylene biosynthesis in germinating leafy surge seeds. Furthermore, the 10 to 578-fold difference in expression of many genes such as HY5 and Histone H3 between two populations at germination, which were treated with and without a constant temperature germination-enhancing pretreatment, revealed disparate impacts on various biosynthetic, growth, signaling, and response processes. Overall, our results indicate a constant temperature pretreatment (20°C for 21 d) is not required for germination of leafy spurge seeds at an alternating temperature. However, the presence or absence of the pretreatment does affect the rate of germination and the germination transcriptional programs.