The putative endo-1,4-β-D-glucanase GLU3 regulates cellulose biosynthesis in barley roots.

The plant cell wall is a crucial structure that ensures plant cell integrity and facilitates environmental adaptation. Cellulose is the primary component of the plant cell wall. Its biosynthesis is orchestrated through the plasma membrane-localized multiprotein cellulose synthase complex, which includes a membrane-anchored endo-1,4-ß-glucanase. Here, we identified a barley (Hordeum vulgare) mutant with short roots resulting from repressed cell division and elongation, which we designated H. vulgare endo-β-1,4-D-glucanase 3-1 (hvglu3-1). HvGLU3 encodes a putative membrane-anchored endo-1,4-ß-glucanase that is highly conserved across plant species. The hvglu3-1 mutant exhibited a 60% reduction in cellulose content, accompanied by changes in hemicellulose and suberin levels and an altered lignin structure in the roots. Subcellular localization analyses and bimolecular fluorescence complementation assays suggested a direct interaction between HvGLU3 and primary cellulose synthases. We investigated the reprogramming of the tissue-specific transcriptome in hvglu3-1 root tips using a combination of laser capture microdissection and RNA sequencing. This approach revealed that 74% of all genes that are actively expressed in the elongation zone are influenced by root cellulose biosynthesis. Gene coexpression analyses highlighted the essential role of cellulose biosynthesis in diverse biological processes, including cell wall organization, phytohormone signaling, and stress responses, to regulate root tissue development. Overall, our study demonstrates the partially conserved role of HvGLU3 in controlling cellulose biosynthesis in roots and provides valuable transcriptomic resources for future studies.