Xylan and lignin deposition are independent of cellulose in the secondary cell wall (Plant Cell)

The secondary cell wall (SCW) plays an important role in the structural integrity of plants and is key to efficient water conductivity. Despite the important role of the SCW, little known about how and when SCW components are assembled. Currently, it is understood that cellulose deposition is a precursor for other components including hemicelluloses and monolignols. A new study from Takenaka et al. is refining the spatial and temporal deposition requirements with regards to the role of cellulose in SCW assembly. Using an inducible expression system to drive expression of two transcription factors that determine metaxylem or protoxylem vessel cell fate and a forward genetic screen, a novel CELLULOSE-SYNTHASE SUBUNIT 7 (CESA7) mutant was identified and named bactulites or cesa7bac. The SCWs in cesa7bac protoxylem vessel cells lack cellulose while the deposition of xylan and lignan are unaffected. Further treatment of the cells with oryzalin, a chemical which depolymerizes microtubules, revealed that the xylan deposition no longer occurred. Taken together, this work reevaluates current understanding of SCW formation and establishes that deposition of xylan and lignin are independent of cellulose deposition. (Summary by Nick Segerson) Plant Cell 10.1105/tpc.18.00292