A team led by Professor Ari Pekka Mähönen at the University of Helsinki has now mapped the missing link. Building on their earlier discovery that cytokinin activates LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors to stimulate radial growth, the researchers reveal how hormonal signals are translated into physical expansion. Their new findings show that cambium LBD (CALBD) proteins regulate cell wall remodeling by promoting the expression of pectate lyase–like (PLL) enzymes, which modify pectin—a key component of the plant cell wall.
Pectin, crucial for cell adhesion and wall flexibility, must be precisely remodeled for cells to enlarge. PLL enzymes break down pectin to adjust wall stiffness, and the study demonstrates that CALBDs function as upstream regulators of this process. Plants engineered to overexpress CALBD showed enhanced radial growth, increased PLL activity, and striking changes in pectin metabolism. In contrast, disrupting CALBD or PLL function led to reduced radial growth. Advanced imaging further revealed distinct patterns of pectin methylesterification in regions of active growth, offering new insights into how plants shape their secondary tissues.
By integrating transcriptome analysis, biochemical assays, and in vivo phenotyping, the team established a clear causal chain linking hormone perception, gene regulation, and structural growth outcomes.
“The plant cell wall is an extremely complex system, with many genes carrying overlapping functions, so screening multiple mutants was both challenging and very time-consuming — but absolutely worth the effort,” said Lingling Ye, a post-doctoral researcher of the Mähönen lab, currently an associate professor at Institute of Emerging Agricultural Technology, Shenzhen University of Advanced Technology, China.
Post-doctoral researcher Xin Wang added, “This was truly a team effort. By collaborating with Dr. Juan José Valle-Delgado from Aalto University and Dr. Julia P. Vainonen and Dr. Maija Sierla from the University of Helsinki, we were able to clearly link changes in cell wall properties to the activity of specific enzymes.”
“Our findings connect cytokinin signaling to changes in the mechanical properties of plant cells,” said Professor Mähönen. “This helps explain how plants integrate hormonal cues with cell wall remodeling to control their shape and size.”
The discovery of the cytokinin–CALBD–PLL pathway significantly advances our understanding of hormone-driven plant growth and opens new research avenues into how cell wall metabolism contributes to plant form and function.