Abstract
The adaptation and survival of boreal and temperate perennials relies on the precise demarcation of the growing season. Seasonal growth and development are defined by day length and temperature signals. Under long-day conditions in spring, poplar FLOWERING LOCUS T2 (FT2) systemically induces shoot growth. In contrast, FT2 downregulation induced by autumnal short days triggers growth cessation and bud set. However, the molecular role of FT2 in local and long-range signaling is not entirely understood. In this study, the CRISPR/Cas9 editing tool was used to generate FT2 loss of function lines of hybrid poplar. Results indicate that FT2 is essential to promote shoot apex development and restrict internode elongation under conditions of long days. The application of bioactive gibberellins (GAs) to apical buds in FT2 loss of function lines was able to rescue bud set. Expression analysis of GA sensing and metabolic genes and hormone quantification revealed that FT2 boosts the 13-hydroxylation branch of the GA biosynthesis pathway in the shoot apex. Paclobutrazol treatment of WT leaves led to limited internode growth in the stem elongation zone. In mature leaves, FT2 was found to control the GA 13-hydroxylation pathway by increasing GA2ox1 and reducing GA3ox2 expression, causing reduced GA1 levels. We here show that in poplar, the FT2 signal promotes shoot apex development and restricts internode elongation through the GA 13-hydroxylation pathway.
Highlights
Growth and development in perennial trees are coordinated by synchronization between plant internal events and environmental cues
Two genome-edited hybrid poplar lines were identified which show a predicted nonfunctional FLOWERING LOCUS T2 (FT2) gene because of a frameshift created in the first exon that translates into a truncated protein (Supplementary Figure 3A)
After 2 weeks, wild type (WT) plantlets went into full leaf production featuring three young leaves on each apex, whereas ft2-8 and ft2-10 apices had only 1 or 2 leaves
Summary
Growth and development in perennial trees are coordinated by synchronization between plant internal events and environmental cues. Photoperiod and temperature are the main factors that regulate multiple processes such as dormancy growth reactivation or flowering. In response to a short-day (SD) photoperiod, poplar trees stop their growth and develop buds to protect meristems anticipating colder temperatures. Dual FT2 Function via Gibberellins required to release buds from dormancy (Rohde et al, 2000), warmer temperatures and long-day (LD) conditions trigger bud break and growth reinitiation (Weiser, 1970; Cooke et al, 2012; Singh et al, 2020). The identification of poplar orthologs of FLOWERING LOCUS T (FT), FT1, and FT2, as flowering and seasonal mediators of perennial growth–dormancy cycles was an important breakthrough in defining the molecular framework that orchestrates these transitions (Bohlenius et al, 2006; Hsu et al, 2011). The physiological and molecular functions of FT2 during the poplar growing season remain unclear
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call