Activity–dormancy transition in the cambial meristem involves stage-specific modulation of auxin response in hybrid aspen

Abstract

The molecular basis of short-day-induced growth cessation and dormancy in the meristems of perennial plants (e.g., forest trees growing in temperate and high-latitude regions) is poorly understood. Using global transcript profiling, we show distinct stagespecific alterations in auxin responsiveness of the transcriptome in the stem tissues during short-day-induced growth cessation and both the transition to and establishment of dormancy in the cambial meristem of hybrid aspen trees. This stage-specific modulation of auxin signaling appears to be controlled via distinct mechanisms. Whereas the induction of growth cessation in the cambium could involve induction of repressor auxin response factors (ARFs) and down-regulation of activator ARFs, dormancy is associated with perturbation of the activity of the SKP-Cullin-F-box TIR (SCF TIR ) complex, leading to potential stabilization of repressor auxin (AUX)/indole-3-acetic acid (IAA) proteins. Although the role of hormones, such as abscisic acid (ABA) and gibberellic acid (GA), in growth cessation and dormancy is well established, our data now implicate auxin in this process. Importantly, in contrast to most developmental processes in which regulation by auxin involves changes in cellular auxin contents, day-length-regulated induction of cambial growth cessation and dormancy involves changes in auxin responses rather than auxin content.short days | meristem identity P erennial plants growing in temperate and high-latitude regions anticipate the approach of winter by sensing the associated reduction in day length (1), and when the day length becomes shorter than the critical length permitting growth [short-day signal (SD)], cell division terminates in the meristems (1). Immediately following cessation of cell division, exposure of plants to permissive conditions (e.g., long days) leads to the reversal of growth arrest (2), and this stage of growth arrest is referred to as ecodormancy. Continued exposure of ecodormant plants to short days brings about the transition from ecodormancy to endodormancy (2). The endodormant state is characterized by the inability of the meristems to respond to growth-promotive signals in contrast to the ecodormant state. Exposure to chilling temperatures is required to restore the ability of endodormant meristems to respond to growth-promotive signals and to reinitiate growth subsequently (3).Recently, the photoreceptor PHYA (4) and homologs of the flowering time genes CONSTANS and FT (5, 6) have been shown to be early-acting components in SD-induced growth cessation in trees. The targets and signaling intermediates of the SD pathway downstream of these early-acting components in growth cessation and dormancy remain largely unexplored (7). Although ecodormant and endodormant states can be distinguished physiologically, the molecular mechanisms underlying the establishment of endodormancy and the inability of endodormant meristems to respond to growth-promotive signals have remained elusive.We investigated whether the SD-regulated induction o...

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

“…Involvement of ethylene and abscisic acid signaling in bud formation has also been suggested (16,17). Modulation of auxin response was also found to be important for the transition to dormancy in poplar (18).…”

Photoperiodic growth control in perennial trees

“…Another major lacuna is regarding hormonal control of photoperiodic growth. For example, gibberellins (GA) and auxin 27 play a role in photoperiodic control of growth but the interplay between CO/FT and GA (or auxin) signaling is still not entirely clear. These and other questions not covered here such as the role of clock will hopefully be answered in the coming years.…”

Plant Circadian Rhythms

“…Ultimately, the stimulation of growth by FT, GAs and other hormones, including auxins and cytokinins, must be down-regulated in autumn so that cell divisions of apical and lateral meristems cease. These signalling pathways are not yet entirely clear but include modulation of hormone sensitivity and cell cycle in what is clearly a highly coordinated process (Baba et al, 2011;Karlberg et al, 2011).…”