Chilling of Dormant Buds HyperinducesFLOWERING LOCUS Tand Recruits GA-Inducible 1,3-β-Glucanases to Reopen Signal Conduits and Release Dormancy inPopulus   

Abstract

In trees, production of intercellular signals and accessibility of signal conduits jointly govern dormancy cycling at the shoot apex. We identified 10 putative cell wall 1,3-b-glucanase genes (glucan hydrolase family 17 [GH17]) in Populus that could turn over 1,3-b-glucan (callose) at pores and plasmodesmata (PD) and investigated their regulation in relation to FT and CENL1 expression. The 10 genes encode orthologs of Arabidopsis thaliana BG_ppap, a PD-associated glycosylphosphatidylinositol (GPI) lipid-anchored protein, the Arabidopsis PD callose binding protein PDCB, and a birch (Betula pendula) putative lipid body (LB) protein. We found that these genes were differentially regulated by photoperiod, by chilling (58C), and by feeding of gibberellins GA 3 and GA 4 . GA 3 feeding upregulated all LB-associated GH17s, whereas GA 4 upregulated most GH17s with a GPI anchor and/or callose binding motif, but only GA 4 induced true bud burst. Chilling upregulated a number of GA biosynthesis and signaling genes as well as FT, but not CENL1, while the reverse was true for both GA 3 and GA 4 . Collectively, the results suggest a model for dormancy release in which chilling induces FT and both GPI lipid-anchored and GA 3 -inducible GH17s to reopen signaling conduits in the embryonic shoot. When temperatures rise, the reopened conduits enable movement of FT and CENL1 to their targets, where they drive bud burst, shoot elongation, and morphogenesis.

EARLY BUD-BREAK 1 (EBB1) is a regulator of release from seasonal dormancy in poplar trees

“…Homologies to vernalization have been invoked, but critical differences exist because the vernalization-associated epigenetic mechanism requires sustained division, whereas bud dormancy can be imposed and reset in the same meristem cells (2). Recently, it has been shown that the plasmodesmata connections to the meristem are plugged during dormancy and need to be reopened before growth-promoting signals like FT can reach their target's tissues in the apex (22). Expression of cell-cycle marker genes indicates that after endodormancy establishment, cambium meristem cells are arrested in the G1/S transition and unable to respond to growth-permissive conditions (23).…”

Tracing a key player in the regulation of plant architecture: the columnar growth habit of apple trees (Malus × domestica)

“…In contrast, the transition from dormancy to active growth is characterized by the induction of flowering pathways, RNA metabolism and protein biosynthesis and transport (Larisch et al 2012). It has been found that SAM cells are symplastically isolated during the dormant period due to the formation of a callose block at the plasmodesmata (Rinne and van der Schoot 1998;Rinne et al 2001;Rinne et al 2011). However, it is not yet clear whether there is a causal relationship between the cellular isolation and the activity-dormancy cycle.…”

“…Additionally, the circadian clock might be able to sense temperature in Arabidopsis (Edwards et al 2006;Gould et al 2006). In Populus, FT2 controls growth cessation, bud set and dormancy induction, and FT1 is expressed during the chilling period to induce the transition from the vegetative to the reproductive phase (Böhlenius et al 2006, Hsu et al 2006Rinne et al 2011). Furthermore, overexpression of CEN/TFL1 in Populus causes delayed bud break and altered chilling requirements (Mohamed et al 2010).…”

Mechanisms of vegetative propagation in bulbs : a molecular approach

“…For example, it has been reported that in perennial trees the release of bud dormancy requires the removal of callose in the plamodesmata in order to restore the symplastic connectivity in the meristem (Rinne et al 2011;Rinne et al 2001;Rinne et al 2016). Although we saw there is a vascular connection between the buds and the mother bulb, it is plausible to think that it might not be very functional when callose is not entirely removed from plasmodesmata in dormant buds, and therefore less carbon resources can be remobilized into those buds.…”