By Jian Hu, Changzheng Xu, and Keming Luo
Background: In trees, the vascular cambium is the population of stem cells that laterally divide and as a consequence produce secondary xylem, which is commonly known as wood. The continuous activity of cambial cells determines the quantity of wood production. Multiple hormonal signals are known to rigorously regulate cambial activity. The exogenous application of auxin and gibberellin can promote cambium activity in poplar stems, and common transcriptome changes occur via treatment with these two phytohormones. However, how auxin and gibberellin combinatorially regulate cambial activity in trees remains unknown.
Question: Does the crosstalk of auxin and gibberellin signaling regulate cambial activity in trees, and if so, how does this occur? We addressed this issue by identifying the interactions of the key components of their signaling pathways in poplar.
Findings: The auxin response factor ARF7 acts as a core regulator of cambial activity to integrate both the auxin and gibberellin pathways in poplar. ARF7 interacts with Aux/IAA and DELLA proteins at the same time. When auxin and gibberellin are present, Aux/IAA and DELLA can be degraded, respectively, thereby releasing the ability of ARF7 to activate downstream gene expression. We found that WOX4 (encoding a key cambial regulator) and PIN1 (encoding an auxin efflux transporter) are directly targeted by ARF7. Therefore, the DELLA-ARF7-Aux/IAA complex regulates the crosstalk between auxin and gibberellin, thereby regulating cambial activity in poplar, by targeting the key genes involved in cambial development.
Next steps: Scientists aim to genetically modify trees through molecular breeding to produce more wood and improve wood quality. Our work demonstrates that ARF7 acts as a molecular bridge linking auxin and gibberellin signaling to regulate cambial activity in poplar, thereby providing a key target for the genetic engineering of trees for enhanced wood production.
Jian Hu, Huili Su, Hui Cao, Hongbin Wei, Xiaokang Fu, Xuemei Jiang, Qin Song, Xinhua He, Changzheng Xu and Keming Luo. (2022). AUXIN RESPONSE FACTOR7 integrates gibberellin and auxin signaling via interactions between DELLA and AUX/IAA proteins to regulate cambial activity in poplar. https://doi.org/10.1093/plcell/koac107