Submitted to: Functional and Integrative Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2011
Publication Date: 11/21/2011
Citation: Chao, W.S., Foley, M.E., Dogramaci, M., Anderson, J.V., Horvath, D.P. 2011. Alternating temperature breaks dormancy in leafy spurge seeds and impacts signaling networks associated with HY5. Functional and Integrative Genomics. 11(4):637-649. Interpretive Summary: Leafy spurge is a noxious perennial weed. Leafy spurge seed does not germinate when imbibed at a constant temperature of 20°C, but transfer of these seeds to an alternating 20:30°C (16:8 h) temperature induced germination. To increase our knowledge aimed at future weed management, we examined the effect of temperature on seed dormancy and germination and evaluated the global pattern of gene expression in seeds after transfer to alternating temperature. Patterns of gene expression suggested a developmental switch from non-germinating to germinating state within the first day at alternating temperature, and plant hormones, sugar, reactive oxygen species, and circadian clock signaling were key components for this transition. Upon incubating imbibed seeds for 3 d at alternating temperature, a dramatic increase in cellular activities was observed; many of the metabolic pathways were involved in biosynthesis of amino acids, macromolecules, and energy and carbon skeleton production for subsequent germination. Germinated seeds have an even wider array of cellular activities for seedling growth.
Technical Abstract: Leafy spurge is a noxious perennial weed. Its non-afterripened seeds do not germinate when imbibed at a constant temperature (C) of 20°C for 21 d, but transfer to an alternating temperature (A) induced germination. Changes in the transcriptomes of seed during 1 and 3 d of alternating temperature and seeds that germinated at alternating temperature were examined using the constant temperature incubated seeds as the baseline. Statistical analysis revealed that 597, 1491, and 1329 genes were differentially-expressed (P<0.05) for the comparisons of 21d C vs. 21d C + 1d A, 21 d C vs. 21d C + 3d A, and 21 d C vs. 21d C + Germ (germination), respectively. Functional classifications based on gene set- and sub-network- enrichment analysis were performed to identify pathways, processes, and gene sub-network that underlie transcriptome changes in the seeds as they germinate. Sugars, plant hormone, reactive oxygen species, and circadian clock signaling/pathways were over-represented at 1d A. At 3d A, an increase in cellular activities was observed as the number of over-represented pathways greatly increased. Many of the metabolic pathways were involved in biosynthesis of amino acids, macromolecules, and energy and carbon skeleton production for subsequent germination. The 3d A and germination the pathways and sub-networks were similar; for example, in the over-representation of amino acid biosynthetic pathways. However, germinated seeds have an even wider array of cellular activities such as translation-related pathways, which are most likely for seedling growth.