Hevea brasiliensis coniferaldehyde-5-hydroxylase (HbCAld5H) regulates xylogenesis, structure and lignin chemistry of xylem cell wall in Nicotiana tabacum

Abstract

Key message The HbCAld5H1 gene cloned from Hevea brasiliensis regulates the cambial activity, xylem differentiation, syringyl–guaiacyl ratio, secondary wall structure, lignification pattern and xylan distribution in xylem fibres of transgenic tobacco plants. Abstract Molecular characterization of lignin biosynthesis gene coniferaldehyde-5-hydroxylase (CAld5H) from Hevea brasiliensis and its functional validation was performed. Both sense and antisense constructs of HbCAld5H1 gene were introduced into tobacco through Agrobacterium-mediated genetic transformation for over expression and down-regulation of this key enzyme to understand its role affecting structural and cell wall chemistry. The anatomical studies of transgenic tobacco plants revealed the increase of cambial activity leading to xylogenesis in sense lines and considerable reduction in antisense lines. The ultra-structural studies showed that the thickness of secondary wall (S2 layer) of fibre had been decreased with non-homogenous lignin distribution in antisense lines, while sense lines showed an increase in S2 layer thickness. Maule color reaction revealed that syringyl lignin distribution in the xylem elements was increased in sense and decreased in antisense lines. The immunoelectron microscopy revealed a reduction in LM 10 and LM 11 labelling in the secondary wall of antisense tobacco lines. Biochemical studies showed a radical increase in syringyl lignin in sense lines without any significant change in total lignin content, while S/G ratio decreased considerably in antisense lines. Our results suggest that CAld5H gene plays an important role in xylogenesis stages such as cambial cell division, secondary wall thickness, xylan and syringyl lignin distribution in tobacco. Therefore, CAld5H gene could be considered as a promising target for lignin modification essential for timber quality improvement in rubber.

ShF5H1 overexpression increases syringyl lignin and improves saccharification in sugarcane leaves

“…It has been reported that CAld5H (coniferaldehyde 5 hydroxylase) has a different activity compared to F5H as the former is more specific to the downstream pathway. 45 , 46 …”

An R2R3‐MYB network modulates stem strength by regulating lignin biosynthesis and secondary cell wall thickening in herbaceous peony

“…Studies have clearly shown that a set of irregular xylem ( IRX ) genes, IRX1 , IRX3 , IRX5 , IRX7 , IRX8, IRX9 , IRX10 and IRX14 encoding glycosyltransferases (GTs) such as cellulose synthase subunit (CESA) and xylan synthases in plants, have been found to be involved in secondary cell‐wall‐associated cellulose and xylan biosynthesis (Ma et al., 2021; Ratke et al., 2018; Taylor et al., 2003; Zeng et al., 2016). In addition, several lignin biosynthetic genes such as cinnamate 4‐hydroxylase gene ( C4H ) and coniferaldehyde‐5‐hydroxylase gene ( CAld5H ) have been reported to play major roles in the process (Li, Liu, et al., 2020; Pramod et al., 2021). Nevertheless, these structural genes serve limited roles in secondary cell wall thickening compared with regulatory genes, which could be able to regulate a range of downstream target genes to perform multiple functions.…”