HUB2 influences lignification

PIRIN2 (PRN2) was earlier reported as the first known molecular player in the regulation of non-cell-autonomous lignification of xylem vessels in Arabidopsis (Arabidopsis thaliana). In the present study we characterized HUB2 (HISTONE MONOUBIQUITINATION2), one of the protein interactors of PRN2, in relation to lignification. Thus we aim to broaden the understanding of non-cell-autonomous lignification and simultaneously provide new information on a protein, which was previously characterized in other aspects of plant development. Protein interaction was tested by yeast two-hybrid assay, beta-galactosidase enzymatic assay and co-immunoprecipitation assay. The morphology and chemical composition of secondary cell walls of Arabidopsis stems and/or hypocotyls was determined by transmission electron microscopy and pyrolysis-gas chromatography/mass spectrometry. Fourier Transform Infrared (FT-IR) and Raman microspectroscopy were employed for the chemical fingerprinting of individual xylem cell walls. HUB2 promoted the deposition of S-type lignin and suppressed the accumulation of G-type lignin in the secondary cell walls of xylem vessels. Transcriptome analysis revealed that PRN2 and HUB2 antagonistically regulate the expression of specific lignin-related genes, and thus lignification.