Nagoya University elucidates mechanisms regulating plant cell wall structure

A research group including Postdoctoral Researcher Saku Kijima (currently a researcher at the Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)), Assistant Professor Takema Sasaki, Undergraduate Student Yuichiro Kikushima of School of Science, and Professor Yoshihisa Oda at the Graduate School of Science at Nagoya University has jointly revealed a new mechanism by which plants control the cell wall structure. The research was conducted jointly with Associate Professor Daisuke Inoue of the Faculty of Design at Kyushu University, Professor Yuki Kondo of the Graduate School of Science at Osaka University, Associate Professor Soichi Inagaki at the Graduate School of Science at the University of Tokyo, Chief Senior Researcher Shingo Sakamoto and Deputy Director Nobutaka Mitsuda of the Bioproduction Research Institute at AIST, and Associate Professor Masatoshi Yamaguchi of the Graduate School of Science and Engineering at Saitama University. The cell wall that surrounds plant cells performs a diverse set of functions, such as cell shape formation, leaf and root growth, and response to various stresses. As a result, the artificial control of plant cell wall structure by applying the findings of this study is expected to contribute to developing technologies for producing plants morphologically suited for harvesting and plants tolerant to drought stress. The study was published in Nature Communications.

The cell wall is deeply involved in a wide range of phenomena, such as plant cell growth, maintenance of morphology, and creation of water transport channels in the body. Proper regulation of cell wall formation is essential for plant development and survival. Its formation is controlled to occur at the right place at the right time, rather than occurring uniformly all over the cell surface. The microtubule lining under the plasma membrane determines where the cell wall is formed by guiding the position and direction of the movement of cellulose-synthesizing enzymes.

Cells constituting plant vessels form secondary cell walls and undergo programmed cell death. As a result, the cell contents are digested, and a hollow tube for transporting water called the tracheary or vessel element is formed. The secondary cell walls composed of these vessel elements are shaped into characteristic patterns on the cell surface, including annular (banded), helical, reticulate, and pitted patterns. Vessels that develop in young, elastic tissue, called the protoxylem, form easily deformable secondary cell walls in annular, helical, or other patterns. Meanwhile, robust secondary cell walls in reticulate and pitted patterns are formed from the vessels occurring in tissues that have completed elongation and growth, known as the metaxylem. However, the mechanism that determines these types of cell wall structures has been unknown until now.

The research group treated Arabidopsis thaliana with a mutagen and searched for mutants in which the cell wall structure of the vessels was altered. They then isolated a mutant where the vessels that normally form pitted cell walls form annular ones instead. Analysis of the genome of this mutant revealed a mutation in a gene called KNAT7. KNAT7 is a gene that makes a protein called transcription factor, which regulates the expression of other genes. Further analysis showed that KNAT7 suppresses the expression of a gene called formin 11 (FH11). The FH11 protein produced from FH11 promotes the polymerization of a protein called actin and the elongation of actin filaments. The FH11 protein was found to localize to the plasma membrane and promote actin filament polymerization in the vicinity of the plasma membrane. Furthermore, the research group found that the excessive production of actin filaments in the vicinity of the plasma membrane by the action of the FH11 protein affects the elongation of microtubules anchored to the plasma membrane and the distribution of a low molecular weight GTPase called ROP, resulting in a dramatic change in the vessel cell wall type from the pitted to the annular pattern.

Disruption of multiple formin genes in Arabidopsis, along with FH11, led to disturbance of the annular cell wall structure of the protoxylem vessels, indicating that formin is also required to form the annular cell walls in wild-type plants. In the present study, the group found that in vessels, regulation of actin polymerization levels near the plasma membrane affects the elongation of microtubules anchored to the plasma membrane and the distribution of the low molecular weight GTPase ROP, playing a major role in determining the type of cell wall structure. Microtubules and the low molecular weight GTPase ROP are important proteins that determine the cell wall structure in vessels and many other plant cells. The function of actin polymerization shown here may be broadly involved in regulating plant cell wall structure. Moreover, protoxylem vessels with annular cell walls are more flexible to perturbations such as elongation and bending than metaxylem vessels with pitted cell walls.

Artificial regulation of the actin polymerization levels in the cells of various tissues that make up the plant based on the findings of this study is expected to lead to the establishment of technology to produce plants morphologically suited for processing or harvesting and with rupture-resistant vessels that are excellent in water transport.

Journal Information
Publication: Nature Communications
Title: Control of plasma membrane-associated actin polymerization specifies the pattern of the cell wall in xylem vessels
DOI: 10.1038/s41467-025-56866-y