PubMed · 13444114
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W J SCHUBERT, F F NORD. 1957. Lignification.. https://doi.org/10.1002/9780470122631.ch9
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Following the down-selection of 14 Arabidopsis thaliana arogenate dehydratase (ADT) knockout and over-expression (OE) genotypes, the most highly contrasting quadruple knockout adt3/4/5/6 and ADT OE genotypes were subjected to proteomics, metabolomics, and scanning electron microscopy (SEM) analyses as needed, with results compared to Columbia wild-type (WT). The basal adt3/4/5/6 stem cross-sections, ∼70% lignin content reduced, exhibited buckled vessel cell walls and partially detached xylary fibers, in contrast to WT and ADT4m/5 m OE genotypes that did not. Anatomical defects primarily resulted from guaiacyl lignin level reductions in vessels with concomitant increased stem syringyl:guaiacyl (S/G) ratios. Phenylpropanoid and various upstream shikimate-chorismate pathway enzyme abundances, as well as specific monolignol oxidases (laccases/peroxidases), generally increased in adt3/4/5/6 at different stem and rosette leaf growth/development stages, relative to WT. Opposite effects were largely observed with the ADT5m OE genotype. By contrast, flavonoid and glucosinolate pathway enzyme amounts varied. Such enzyme abundance increases were overall unproductive as adt3/4/5/6 was unable to restore WT, ADT4 OE, ADT5 OE, ADT5m OE, and ADT4m/5 m OE secondary metabolite (lignin, phenylpropanoid, lignan, flavonoid, phenolic acid, and glucosinolate) levels. Conversely, ADT OE genotypes did not significantly increase programmed lignin levels or alter S/G compositions. In sum, proteomics analyses of adt3/4/5/6 and adt5 'perceived' that lignin and low molecular weight secondary metabolite amounts were not at 'programmed' levels as for WT and ADT OE genotypes but observed increases in relevant pathway protein abundances were futile. Notably though, proteomics analyses did not lead to predicting that lignin and associated biochemical pathways would have reduced metabolite levels, relative to WT and ADT OE genotypes. Genotype adt3/4/5/6, possibly the highest lignin level reduced genotype reported, did not utilize other phenolics to compensate. By contrast, the differential temporal and spatial deposition of cell wall oxidases again indicate the exquisite control over lignin deposition, and our lack of knowledge of precise lignin structure and assembly in subcellular regions of the lignified cell walls.
Although bamboo can be an ideal raw material for pulp and paper industry, the depolymerization of its complex polymers needs to be facilitated. The deposition of lignin is influenced by cinnamyl alcohol dehydrogenase (CAD), an enzyme that catalyzes the formation of monolignol precursors. Here, we identified 18 DfCAD genes in Dendrocalamus farinosus and revealed using bioinformatics methods, DfCAD16 functions as the primary enzyme in the synthesis pathway of guaiacyl (G)-lignin. Phenotypic analysis of plants overexpression DfCAD16 exhibited remarkable increasing in G-lignin. Furthermore, we demonstrated that an R2R3-type MYB transcription factor DfMYB12 could directly bind to the promoter region of DfCAD16 and activate its expression both in vitro and in vivo. Our findings revealed that DfMYB12-DfCAD16 is a key regulatory factor governing G-lignin biosynthesis in D. farinosus. These insights can be used for improving bamboo varieties for pulp production.
Pear stone cell lignification, a critical determinant of fruit texture and quality, is regulated by developmental and environmental cues, with abscisic acid (ABA) playing a central role. However, the molecular mechanisms underlying its role in reactive oxygen species (ROS)-mediated lignification remain unclear. Here, we show that PuABI5, a key component in ABA signaling, directly combines with PuMYB169, the master regulator of stone cell lignification, to modulate ROS production and lignin biosynthesis in pear fruit. Exogenous application of ABA enhances H2O2 and lignin accumulation in both pear fruits and calli, and ABA-activated PuABI5 positively regulates stone cell lignification. We demonstrate that ABA-induced PuABI5 binds directly to the PuMYB169 promoter and activates its expression to promote the transcription of PuRBOHF and lignin-related genes, thereby enhancing ROS production and lignin accumulation. Notably, PuABI5 interacted with PuMYB169 to enhance the induction of PuRBOHF expression, leading to elevated levels of H2O2, which feedback to strengthen the interaction between PuABI5 and PuMYB169. Collectively, our findings elucidate that ABA induces ROS-mediated lignification of stone cells in pears by activating the PuABI5-PuMYB169 transcriptional module.