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-β-glucanase genes (glucan hydrolase family 17 [GH17]) in Populus that could turn over 1,3-β-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 (5°C), 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.
Highlights
Developmental transitions in plants rely on endogenous mechanisms that are triggered by environmental cues
We investigated if the CO/FLOWERING LOCUS T (FT) module becomes operational in the leaves of the embryonic shoot itself and found that in the dormant bud, CO was upregulated ;3-fold after 2 weeks of chilling and that it remained at that level throughout the rest of chilling period (Figure 7A)
The cycling of perennial plants through phases of growth and dormancy is based on a series of developmental events that are the apex and the phloem (Aloni et al, 1991; Aloni and Peterson, 1997; Rinne et al, 2001)
Summary
Developmental transitions in plants rely on endogenous mechanisms that are triggered by environmental cues. A well-studied transition is that of flowering, in which the shoot apical meristem (SAM) transforms into an inflorescence meristem that produces the inflorescence and floral buds. The perennial SAM has the additional and unique capacity to assume a dormant and freezing tolerant state in response to a declining photoperiod (Weiser, 1970; Welling et al, 1997; Rinne et al, 2001). The first signs preceding this response are the cessation of growth and the emergence of a bud, events that unfold rapidly, in northern ecotypes (Bohlenius et al, 2006). The sequence of events that culminates in photoperiodinduced transitions relies on remote communication, and research on flowering has identified the signaling peptide FLOWERING LOCUS T (FT) as a major long-distance signal. FT is produced in the vasculature of leaves by action of CONSTANS (CO) and sent
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