Lignin is a main component of the secondary cell wall in vessels and fibers of xylem tissue. However, the significance of lignin in cell physiology during plant growth is unclear. In this study, we generated lignin-modified
Populus
via cell-specific downregulation of the 4-coumarate-CoA ligase gene (
4CL
). The transgenic plants with selective lignin modification in vessel elements or fiber cells allowed us to investigate how lignin affects the physiology of vessel or fiber cells in relation to plant growth. Results showed that vessel-specific suppression of lignin biosynthesis resulted in deformed vessels and normal fibers, while fiber-specific suppression of lignin biosynthesis led to less-lignified fibers and normal vessels. Further analyses revealed that the efficiency of long distance water transport was severely affected in transgenics with vessel-specific lignin modification, while minimal effect was detected in transgenics with fiber-specific lignin modification. Vessel-specific lignin reduction led to high susceptibility to drought stress and poor growth in field, likely due to vessel defects in long distance transport of water. The distinct physiological significance of lignin in different cell types provides insights into the selective modification of lignin for improvement of lignocellulosic biomass utilization.
SummaryIn trees, lateral growth of the stem occurs through cell divisions in the vascular cambium. Vascular cambium activity is regulated by endogenous developmental programmes and environmental cues. However, the underlying mechanisms that regulate cambium activity are largely unknown. Genomic, biochemical and genetic approaches were used here to elucidate the role of PtrCLE20, a CLAVATA3 (CLV3)/embryo surrounding region (ESR)‐related peptide gene, in the regulation of lateral growth in Populus. Fifty‐two peptides encoded by CLE genes were identified in the genome of Populus trichocarpa. Among them PtrCLE20 transcripts were detected in developing xylem while the PtrCLE20 peptide was mainly localized in vascular cambium cells. PtrCLE20 acted in repressing vascular cambium activity indicated by that upregulation of PtrCLE20 resulted in fewer layers of vascular cambium cells with repressed expression of the genes related to cell dividing activity. PtrCLE20 peptide also showed a repression effect on the root growth of Populus and Arabidopsis, likely through inhibiting meristematic cell dividing activity. Together, the results suggest that PtrCLE20 peptide, produced from developing xylem cells, plays a role in regulating lateral growth by repression of cambium activity in trees.
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