Overlapping Genes Associated with Dormant and Non-Dormant Seeds and Buds of Leafy Spurge (Euphorbia esula)

Leafy spurge (Euphorbia esula L.) is a herbaceous perennial weed. Bud dormancy in leafy spurge exhibits three well-defined phases of para-, endo- and ecodormancy; however, seed dormancy for leafy spurge is classified as physiological dormancy that requires stratification for dormancy release. Overlaps between different phases of bud and seed dormancy have not been determined. Thus, here we compared various phases of dormancy between seeds and buds to identify overlapping genes and molecular processes, which should provide new insights about common regulators of dormancy. For this study, seeds incubated at a constant temperature of 20°C for 21 days (21d C) were compared to paradormant buds (Para) because seeds may be inhibited by endosperm-generated signals, or compared to ecodormant buds (Eco) because seeds germinate after being subjected to alternating temperature ([A] 20:30°C/16:8 h). Additionally, two-day growth-induced seeds (21d C + 2d A) were compared with two-day growth-induced buds (2d-growth). Since neither endodormant buds (Endo) nor seeds incubated for 1 day at the constant temperature of 20°C (1d C) will germinate at optimal growth conditions, they were used as common baselines in these studies. We first determined transcript abundance within buds (i.e. Para or Eco to Endo) and seeds (i.e. 21d C to 1d C) for ~200 growth-related genes by qRT-PCR and t-tests; overlapping genes were then identified between buds and seeds. Transcript abundance revealed that 14 differentially-expressed genes overlap between buds and seeds for the ‘Para to Endo’ and ‘21d C to 1d C’ comparison, and 9 of these show a common trend in expression pattern. These 9 transcripts are associated with cell cycle (HisH4), stress response/transcription factors (ICE2, ERFB4/ABR1), ABA and auxin response (ABA1, ARF1, IAA7, TFL1), and transport (ABCB2). Transcript abundance for the ‘Eco to Endo’ and ‘21d C to 1d C’ comparison identified 10 differentially-expressed genes that overlap between buds and seeds, and only 3 of these show a common trend in expression. These results indicate that the physiological state of 21d C seeds is more analogous to paradormant buds than that of ecodormant buds. To compare initiation of shoot growth from buds and seeds, two-day growth-induced seeds (21d C + 2d A vs. 1d C) were compared with two-day growth-induced buds (2d growth vs. Endo), and 6 overlapping transcripts were identified. Three of these transcripts show a common trend in expression pattern. These 3 transcripts are involved in cell wall extensibility (EXP6) and auxin transport (PID, PIN3). Our combined results indicate that overlaps of molecular mechanism involved in dormancy transitions of buds and seeds likely involve processes associate with ABA and auxin signaling and transport, cell cycle, and AP2/ERF transcription factors or their up-stream regulators