Dual role of tree florigen activation complex component FD in photoperiodic growth control and adaptive response pathways

Abstract

A complex consisting of evolutionarily conserved FD, FLOWERING LOCUS T (FT) proteins is a regulator of floral transition. Intriguingly, FT orthologs are also implicated in developmental transitions distinct from flowering, such as photoperiodic control of bulbing in onions, potato tuberization, and growth cessation in trees. However, whether an FT-FD complex participates in these transitions and, if so, its mode of action, are unknown. We identified two closely related FD homologs, FD-like 1 (FDL1) and FD-like 2 (FDL2), in the model tree hybrid aspen. Using gain of function and RNAisuppressed FDL1 and FDL2 transgenic plants, we show that FDL1 and FDL2 have distinct functions and a complex consisting of FT and FDL1 mediates in photoperiodic control of seasonal growth. The downstream target of the FT-FD complex in photoperiodic control of growth is Like AP1 (LAP1), a tree ortholog of the floral meristem identity gene APETALA1. Intriguingly, FDL1 also participates in the transcriptional control of adaptive response and bud maturation pathways, independent of its interaction with FT, presumably via interaction with ABSCISIC ACID INSENSITIVE 3 (ABI3) transcription factor, a component of abscisic acid (ABA) signaling. Our data reveal that in contrast to its primary role in flowering, FD has dual roles in the photoperiodic control of seasonal growth and stress tolerance in trees. Thus, the functions of FT and FD have diversified during evolution, and FD homologs have acquired roles that are independent of their interaction with FT. 5), is critical for the formation of protein complexes to control flowering via transcriptional control of downstream targets [e.g., floral meristem identity genes, transcription factors APETALA1 (AP1) and OsMADS1]. Whereas the FT-FD complex promotes flowering at the shoot apical meristem (4), BRC1 appears to delay floral transition at the axillary meristem (5). These findings indicate that depending upon its interaction partner, FT-containing complexes can have distinct roles. The structure of FT-FD complex elucidated in rice has shown that a 14-3-3 protein mediates the interaction between rice FT homolog HEADING DATE 3a (Hd3a) and FD homolog OsFD1 via the C-terminally located SAP (serine alanine proline) motif in OsFD1 to generate the active nuclear localized florigen activation complex (3).Interestingly, FT homologs are also involved in the control of diverse developmental transitions distinct from flowering, such as tuberization in potatoes (6), bulb formation in onions (7), stomatal opening (8), and photoperiodic control of seasonal growth in trees (9-11). These observations suggest that complexes of FT are not only important to the control of flowering but have a broader functionality. However, the mechanisms underlying the functional diversity of the FT complexes and how they can participate in the control of developmental pathways distinct from flowering are not well understood because, in contrast to FT, FD or BRC1 (or other interactors of FT), which provide DNA binding ability to ...

The Multiple Signals That Control Tuber Formation

“…These include bud dormancy in Vitis vinifera (Vergara et al, 2016), seasonal control of growth in Populus spp. (Böhlenius et al, 2006;Tylewicz et al, 2015), bud dormancy in conifers (Gyllenstrand et al, 2007), meristem growth termination in tomato (Solanum lycopersicum; Shalit et al, 2009), and tuberization in potato (Navarro et al, 2011). Overall, these observations suggest that FT orthologs may function as mobile signals in meristem-associated transitions in nonfloral pathways.…”

Functional characterization of DEMETER-like DNA demethylases during growth-dormancy cycles in poplar

“…Upregulation of flavonoid biosynthesis have been shown as molecular markers of bud maturation (Ruttkink et al 2007;Tylewicz et al 2015). Our transcriptome analyses revealed three upregulated genes in CsDML OX plants encoding putative enzymes belonging to the flavonoids biosynthetic pathway.…”

“…They were a chalcone synthase (CHS), a quercetin 3-Oglucosyltransferase (3GT) and a dihydroflavonol 4-reductase (DFR) (Table S5.1). CHS and DFR enzymes are known to be involved in the early steps of flavonoid biosynthesis (Ono et al 2010), so upregulation of these genes in CsDML OX plants could correlates with their early red coloring during bud maturation Tylewicz et al 2015).…”

“…The later includes differentiation of leaf primordia into bud scales alongside with the formation of the embryonic shoot. Bud scales accumulate flavonoid components leading to their characteristic red-brown color (Rohde et al 2002;Tylewicz et al 2015). In addition to the above-mentioned transformations, the SD signal promotes the acquisition of cold and desiccation tolerance in apical and cambial meristems before they become dormant (Rohde et al 2002;Rohde & Bhalerao 2007;Ruttink et al 2007;.…”

“…found to play a role in growth cessation under SD conditions in poplar apices Petterle et al 2013;Azeez et al 2014;Tylewicz et al 2015). Phytochrome photoreceptors and circadian clock core components upstream of these genes have also been implicated in the early regulation of growth cessation by SD (Kozarewa et al 2010;Ibañez et al 2010;.…”