Live-cell imaging by laser scanning confocal microscopy (LCSM) is used here to show Golgi-localization of enzymes involved in plant cell wall assembly.
Understanding the regulation and assembly of plant cell walls

The Held Lab

Held Lab Members

My research is aimed at helping to uncover the integration of regulatory mechanisms that govern plant cell wall biosynthesis. I am also interested in merging biophysical and biochemical studies to better understand cell wall polymer self-assembly.

Current Research Topics

Wall assembly

Plant cell walls are composites of polysaccharide, glycoprotein, and phenolic polymers. With some exceptions (e.g. cellulose, callose, and lignin), cell wall polymers are synthesized in the plant Golgi apparatus, trafficked in vesicles to the plasma membrane, and then secreted to the wall. Upon their delivery to the wall, these polymeric networks coalesce to form complex cell walls. How these polymers assemble in cells walls and what drives their intermolecular interactactions is murky. Complex structures, like cell walls, are generally assembled from simpler substructures. Somewhat like the "parable of the watchmakers" (Herbert Simon, 1968), initial sub-assemblies likely serve as templates, or scaffolds for higher-ordered, more complexes assemblies. Hence my lab’s interest in extensin (EXTs) glycoproteins. EXTs are an important class of plant cell wall structural glycoproteins, that are rich in hydroxyproline (Hyp). Although not very abundant in the wall, EXTs are important scaffolding molecules for wall assembly for at least four main reasons:

  1. They are highly periodic, repetitive glycoproteins.
  2. Through their repetitive nature, they are highly amphiphilic (essentially acting as block co-polymers)
  3. They are secreted early in primary wall formation.
  4. And they are highly basic glycoproteins and are known interact ionically with acidic pectins.

My previous work has investigated the covalent crosslinking of EXT glycoproteins, but now I am currently focused on defining their self-assembly using a combination of biochemical and biophysical studies.

Post-transcriptional regulation of wall biosynthesis

Plant cell wall biosynthesis is a highly coordinated process at the gene expression level. Distinct sets of genes are activated and repressed for both primary and secondary wall biosynthesis.  Transcriptional regulatory networks that govern the transition from primary to secondary cell wall biosynthesis are more well known. However, previous research in my lab has indicated a role for cellulose synthase-derived small RNAs in the post-transcriptional regulation of wall biosynthesis. Unlike the transcriptional regulatory networks, post-transcriptional regulation of cell wall biosynthesis is not well understood. My lab is currently working on the identification of specific small RNAs that can affect wall biosynthesis using both small RNA next-generation sequencing (sRNA-NGS) and bioinformatic techniques.