Uncover the mechanism by which poplar measures the night hours to determine its annual growth period

Researchers at the Centro de Biotecnología y Genómica de Plantas (CBGP, UPM-INIA) are leading an international study that shows how a circadian clock gene in poplars acts as a molecular sensor to quantify the number of night hours and determine the cessation of autumnal growth.


In the boreal and temperate regions, one of the most important adaptations that trees must develop is the cessation of growth to prepare for winter. One of the main reasons for this is the protection of tissues responsible for resuming tree growth in the next vegetative season. In these latitudes, the photoperiod (daylight hours) is considered the most important environmental signal, with short days being the repressive signal of growth.


A team of researchers led by Isabel Allona and Mariano Perales, from theCentro de Biotecnología y Genómica de Plantas(CBGP-UPM/INIA), joint centre of the Universidad Politécnica de Madrid and the Instituto de Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), , has revealed a new molecular mechanism that participates in the photoperiodic regulation of poplar.


To do this, the UPM researchers relied on previous studies conducted with Arabidopsis thaliana, a long-day facultative plant, in which the decision to flower is explained by an external coincidence model. According to this model, "the protein that activates flowering (FT) is produced only when its activator (CO) is active during daylight hours." This same model was proposed to explain the photoperiodic control of the cessation of tree growth. However, these two models have a difference, high levels of the activator (CO) are not enough to induce poplar growth in short day conditions as is the case in Arabidopsis. These data suggest an additional repressive mechanism in trees, so in this work, we focus on deciphering the importance of night hours in the cessation of growth, obtaining original and interesting results”, explains the researcher at CBGP and Professor at the Escuela Técnica Superior de Ingeniería Agronómica, Alimentaria y de Biosistemas(ETSIAAB) of the UPM, Isabel Allona.



Control of growth cessation with more night hours

The work developed by the UPM researchers shows that the circadian clock gene, LHY2, increases its expression in proportion to the night hours. "We also show that this increase is dependent on the length of the night and not on its advance," she says.


“Regarding the expression of the FT2 gene, which regulates flowering and apical growth in trees, we observe the opposite. A quantitative decrease in the accumulation of messenger RNA (which communicates the information contained in the DNA), occurs whenever we extend the night. "Besides, the repressive effects of the short day disappear when it is interrupted with a pulse of red light, simulating the cessation of the night," adds Mariano Perales.


Using advanced molecular and genetic techniques, the UPM researchers in collaboration with those of the Sainsbury Laboratory at the University of Cambridge, UK, demonstrated the participation of the LHY2 gene in the direct repression of the FT2 gene. With all this, the experts proposed a molecular model of a repressor mechanism through which the tree can quantitatively integrate the night hours, using this information to regulate growth cessation. This work has been published in Current Biology.


Ramos-Sánchez JM, Triozzi PM, Alique D, Geng F, Gao M, Jaeger KE, Wigge PA, Allona I, Perales M. LHY2 Integrates Night-Length Information to Determine Timing of Poplar Photoperiodic Growth. Curr Biol. 2019 Jul 22;29(14):2402-2406.e4. doi: 10.1016/j.cub.2019.06.003. Epub 2019 Jun 27.