Induction of endodormancy in crown buds of leafy spurge (Euphorbia esula L.) implicates a role for ethylene and cross-talk between photoperiod and temperature.

Leafy spurge is a model for studying well-defined phases of dormancy in underground adventitious buds (UABs) of herbaceous perennial weeds, which is a primary factor facilitating their escape from conventional control measures. A 12-week ramp down in both temperature (27 → 10 °C) and photoperiod (16 → 8 h light) is required to induce a transition from para- to endo-dormancy in UABs of leafy spurge. To evaluate the effects of photoperiod and temperature on molecular networks of UABs during this transition, we compared global transcriptome data-sets obtained from leafy spurge exposed to a ramp down in both temperature and photoperiod (RDtp) versus a ramp down in temperature (RDt) alone. Analysis of data-sets indicated that transcript abundance for genes associated with circadian clock, photoperiodism, flowering, and hormone responses (CCA1, COP1, HY5, MAF3, MAX2) preferentially increased in endodormant UABs. Gene-set enrichment analyses also highlighted metabolic pathways involved in endodormancy induction that were associated with ethylene, auxin, flavonoids, and carbohydrate metabolism; whereas, sub-network enrichment analyses identified hubs (CCA1, CO, FRI, miR172A, EINs, DREBs) of molecular networks associated with carbohydrate metabolism, circadian clock, flowering, and stress and hormone responses. These results helped refine existing models for the transition to endodormancy in UABs of leafy spurge, which strengthened the roles of circadian clock associated genes, DREBs, COP1-HY5, carbohydrate metabolism, and involvement of hormones (ABA, ethylene, and strigolactones). We further examined the effects of ethylene by application of 1-aminocyclopropane-1-carboxylate (ACC) to paradormant plants without a ramp down treatment. New vegetative growth from UABs of ACC-treated plants resulted in a dwarfed phenotype that mimicked the growth response in RDtp-induced endodormant UABs. The results of this study provide new insights into dormancy regulation suggesting a short-photoperiod treatment provides an additive cross-talk effect with temperature signals that may impact ethylene's effect on AP2/ERF family members.