PIRIN2 suppresses S‐type lignin accumulation in a noncell‐autonomous manner in Arabidopsis xylem elements

Abstract

PIRIN (PRN) genes encode cupin domain-containing proteins that function as transcriptional co-regulators in humans but that are poorly described in plants. A previous study in xylogenic cell cultures of Zinnia elegans suggested a role for a PRN protein in lignification. This study aimed to identify the function of Arabidopsis (Arabidopsis thaliana) PRN proteins in lignification of xylem tissues.Chemical composition of the secondary cell walls was analysed in Arabidopsis stems and/or hypocotyls by pyrolysis-gas chromatography/mass spectrometry, 2D-nuclear magnetic resonance and phenolic profiling. Secondary cell walls of individual xylem elements were chemotyped by Fourier transform infrared and Raman microspectroscopy.Arabidopsis PRN2 suppressed accumulation of S-type lignin in Arabidopsis stems and hypocotyls. PRN2 promoter activity and PRN2:GFP fusion protein were localised specifically in cells next to the vessel elements, suggesting a role for PRN2 in noncell-autonomous lignification of xylem vessels. Accordingly, PRN2 modulated lignin chemistry in the secondary cell walls of the neighbouring vessel elements.These results indicate that PRN2 suppresses S-type lignin accumulation in the neighbourhood of xylem vessels to bestow G-type enriched lignin composition on the secondary cell walls of the vessel elements. Gene expression analyses suggested that PRN2 function is mediated by regulation of the expression of the lignin-biosynthetic genes.

The chromatin-modifying protein HUB2 is involved in the regulation of lignin composition in xylem vessels

“…Arabidopsis T-DNA insertion mutants used in this study included prn2-1 (SM_3.15394), prn2-2 (SALK_079571), hub2-1 (GABI_634H04), hub2-2 (SALK_071289), c4h-3 (ref3.3), and ccr1-3 (SALK_123689), which all have been described previously ( Ruegger and Chapple, 2001 ; Fleury et al , 2007 ; Cao et al , 2008 ; Mir Derikvand et al ., 2008 ; Zhang et al , 2020 a ). The PRN2 -overexpressing lines 6 and 13 (overexpression under the control of the 35S promoter) have been described in Zhang et al .…”

“…The PRN2 -overexpressing lines 6 and 13 (overexpression under the control of the 35S promoter) have been described in Zhang et al . (2014 , 2020 a ).…”

“…Pools of freeze-dried Arabidopsis stem and hypocotyl samples were ball-milled as described by Zhang et al (2020 a ). A 60±10 μg aliquot of ball-milled powder was then applied to the pyrolizer (PY-2020iD and AS1020E, FrontierLabs, Japan) attached to a GC/MS (7890A/5975C, Agilent Technologies AB Sweden, Kista, Sweden).…”

“…Transverse sections (20 μm thick) were cryo-sectioned from the hypocotyls of 8-week-old Arabidopsis plants. Fourier transfer infared (FT - IR) and Raman microspectroscopic measurements were performed according to previous protocols ( Gorzsás et al ., 2011 , 2017 ) and experimental parameters ( Zhang et al , 2020 a ). For FT-IR spectra, section thickness resulted in saturation in the carbohydrate region, limiting the spectral range used in the analysis (see below).…”

“…We recently showed that the PIRIN2 (PRN2) protein suppresses S-type lignin biosynthesis in the secondary cell walls of xylem vessels in Arabidopsis ( Zhang et al , 2020 a ). PIRIN2 belongs to a rather poorly described cupin domain-containing family of proteins with four members in Arabidopsis ( Zhang et al , 2020 a ). Our data supported that PRN2 regulates lignification by controlling the transcription of lignin biosynthetic genes.…”