Flowering Gene Homologs Regulate Seasonal Growth Changes in Poplar

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Virginia Tech

The adaptation of trees to temperate and boreal climates depends on their ability to respond to environmental signals that are markers of seasonal changes in order to survive winter and maximize growth. The genus Populus (poplars) is a model system for identifying the genes and molecular mechanisms that regulate growth and dormancy transitions. Photoperiod and temperature regulate both vegetative and floral phenology. FLOWERING LOCUS T (FT) and FLOWERING LOCUS D (FD) are key regulators of flowering time in Arabidopsis and other plants. The distinct functions of three poplar FD-LIKE (FDL) genes and two FTs were explored through gain-of-function, dominant repression, and CRISPR/CAS9-mediated gene editing. We studied trees in controlled environments, including manipulation of daylength and temperature to mimic an annual seasonal growth and dormancy cycle. Our studies showed that the FDL proteins share less than complete functional equivalency. Among the three paralogs, only FDL2.2 promoted precocious flowering, whereas FDL1 and FDL3 appear to have distinct roles in vegetative growth and phenology. Whereas overexpression of any FDL gene delays short day-induced growth cessation and bud set, only FDL3 coordinately altered leaf development and the transition to secondary growth in a photoperiod-dependent manner. For the first time, we demonstrate distinct functions of the two FT paralogs in vegetative phenology. Study of ft1ft2 double mutants and ft1-specific mutants showed that FT1 promotes dormancy release, whereas FT2 is necessary to sustain growth. Collectively, our results reveal that poplar FTs and FDLs have distinct roles in controlling different aspects of vegetative phenology and woody shoot development.

FT-FD interaction complex, vegetative growth, dormancy release, photoperiodic response, Populus