"Shadow government": how transcription factors regulate plant cell wall formation

The plant cell wall is a dynamic, structurally complex supramolecular compartment essential for the development, defense, and adaptation of plants to their environment. While the biosynthesis and transcriptional regulation of secondary cell walls (SCWs) have been extensively studied and are relatively well characterized, the hierarchical transcriptional regulatory networks (TRNs) orchestrating the formation of primary and tertiary cell walls (PCWs and TCWs) remain less well understood. Although all plant cells possess PCWs, the regulation of their biosynthesis remains enigmatic. Even less is known about TCWs, which are exclusive to fibers. This review offers a comprehensive summary of the current understanding of the transcriptional regulation of plant cell wall biosynthesis, highlighting recent progress as well as ongoing knowledge gaps. We examine the inherent challenges in studying PCWs, given their indispensable role in cell viability, which complicates experimental dissection. Meanwhile TCW formation, inherent to specialized mechanical tissue such as sclerenchyma, is controlled by a distinct tissue-specific regulatory program, elements of which remain unidentified and appear fundamentally different from those of the SCW TRN, despite TCWs being considered a layer within SCWs. Though these programs remain elusive, they exhibit all the characteristics of a well-organized "shadow government": influential, precisely coordinated, and remarkably difficult to detect. By synthesizing insights across diverse plant systems and incorporating the latest genomic and transcriptomic approaches, this review outlines the current state of plant cell wall regulation research and identifies promising directions for future investigation.