背景回顾：The seasonally synchronized annual growth cycle that is regulated mainly by photoperiod and temperature cues is a crucial adaptive strategy for perennial plants in boreal and temperate ecosystems. Phytochrome B (phyB), as a light and thermal sensor, has been extensively studied in Arabidopsis. 

提出问题：However, the specific mechanisms for how the phytochrome photoreceptors control the phenology in tree species remain poorly understood. 

主要研究：We characterized the functions of PHYBgenes and their downstream PHYTOCHROME INTERACTING FACTOR (PIF) targets in the regulation of shade avoidance and seasonal growth in hybrid aspen trees. 

结果1-phyB1/2：We show that while phyB1 and phyB2, as phyB in other plants, act as suppressors of shoot elongation during vegetative growth, they act as promoters of tree seasonal growth. 

结果2-PIFs：Furthermore, while the Populus homologs of both PIF4 and PIF8 are involved in the shade avoidance syndrome (SAS), only PIF8 plays a major role as a suppressor of seasonal growth. 

结果3-转录组：Our data suggest that the PHYB‐PIF8 regulon controls seasonal growth through the regulation of FT and CENL1 expression while a genome‐wide transcriptome analysis suggests how, in Populus trees, phyB coordinately regulates SAS responses and seasonal growth cessation.

 摘 要 

季节同步性年生长周期主要受到光周期和温度信号的调控，是北方和温带多年生植物的重要适应策略。phyB是植物中感知光和温度的感受器，在拟南芥中的相关功能研究比较深入。但是，光敏色素光受体控制树木物候的分子机制还有待进一步研究。本文中，作者鉴定了PHYB基因及其下游PIFs在调控杂交白杨的避荫和季节性生长方面的功能。作者发现，phyB是其它植物在营养生长过程中茎伸长的抑制因子，而phyB1和phyB2是树木季节性生长的促进因子。此外，虽然杨树的PIF4和PIF8基因均参与避荫综合症（SAS），但是仅PIF8作为杨树季节性生长的抑制因子发挥主要作用。本文的研究揭示了phyB如何协调调控杨树的避荫响应和季节性生长停止，即通过全基因组范围的转录分析显示，PHYB‐PIF8调控子通过调控FT和CENL1的表达，控制树木的季节性生长。