A New Mechanism Identified For How Plant Hormones Promote Wood Formation

Researchers at the University of Helsinki have discovered a mechanism that allows plants to regulate the ratio of produced wood (i.e. xylem) and phloem. Both tissues are formed by the vascular cambium. The discovery is important for understanding the factors that regulate tree growth.

Cross section of Arabidopsis root showing auxin transporter PIN1 expression (Image: Riikka Mäkilä ) Earlier studies in Professor Ari Pekka Mähönen’s research group have shown that plant hormone auxin is important for positioning stem cells within the vascular cambium. When a stem cell divides, one of the daughters remains a stem cell while the other one differentiates. However, how vascular cambium decides whether a cell will differentiate into wood or phloem has been unclear.

In this study, Riikka Mäkilä, a doctoral researcher in Mähönen’s group, discovered that plant hormone gibberellic acid (GA) regulates the ratio of how much xylem and phloem the cambium is producing. Specifically, GA does this by promoting the transport and signalling of the plant hormone auxin in the vascular cambium. When plants have more GA, they increase their auxin transport and signalling, which makes the stem cell daughter differentiate into wood more often than phloem, thus increasing wood production.

The discovery is important for understanding the factors that regulate tree growth and may provide new applicable knowledge for tree breeding.

Global warming and rising carbon dioxide (CO2) levels are greatly impacting humans and nature. Sequestering carbon is an efficient way to slow down these effects. Plants, especially trees, can sequester CO2 and store it in their trunks as wood.

“Wood is produced by cell divisions in the vascular cambium, but this tissue can also make phloem. Thus, it is important to understand how the production of these tissues is balanced. Due to the long generation times and difficulties in tree genetic manipulations, researchers use Arabidopsis thaliana root as a model, as it has structures similar to a tree trunk. Later, the knowledge gained from Arabidopsis can be transferred to tree breeding,” Mäkilä says.

Publication:  Mäkilä, R., et al. Gibberellins promote polar auxin transport to regulate stem cell fate decisions in cambium. Nature Plants, (2023). DOI: 10.1038/s41477-023-01360-w

Original Story Source: University of Helsinki