Abstract
Lignin biosynthesis enzymes form complexes for metabolic channelling during lignification and these enzymes also play an essential role in biotic and abiotic stress response. Cinnamyl alcohol dehydrogenase (CAD) is a vital enzyme that catalyses the reduction of aldehydes to alcohols, which is the final step in the lignin biosynthesis pathway. In the present study, we identified 49 CAD enzymes in five Bambusoideae species and analysed their phylogenetic relationships and conserved domains. Expression analysis of Moso bamboo PheCAD genes in several developmental tissues and stages revealed that among the PheCAD genes, PheCAD2 has the highest expression level and is expressed in many tissues and PheCAD1, PheCAD6, PheCAD8 and PheCAD12 were also expressed in most of the tissues studied. Co-expression analysis identified that the PheCAD2 positively correlates with most lignin biosynthesis enzymes, indicating that PheCAD2 might be the key enzyme involved in lignin biosynthesis. Further, more than 35% of the co-expressed genes with PheCADs were involved in biotic or abiotic stress responses. Abiotic stress transcriptomic data (SA, ABA, drought, and salt) analysis identified that PheCAD2, PheCAD3 and PheCAD5 genes were highly upregulated, confirming their involvement in abiotic stress response. Through yeast two-hybrid analysis, we found that PheCAD1, PheCAD2 and PheCAD8 form homo-dimers. Interestingly, BiFC and pull-down experiments identified that these enzymes form both homo- and hetero- dimers. These data suggest that PheCAD genes are involved in abiotic stress response and PheCAD2 might be a key lignin biosynthesis pathway enzyme. Moreover, this is the first report to show that three PheCAD enzymes form complexes and that the formation of PheCAD homo- and hetero- dimers might be tissue specific.
Highlights
IntroductionLignin is the major component of the secondary cell wall and is the most abundant aromatic compound produced by plants
To characterise the Moso bamboo Cinnamyl alcohol dehydrogenase (CAD) enzymes, we identified them from a P. edulis genome database using the rice CAD protein sequences as a reference
A total of 14 PheCAD enzymes were identified in the Moso bamboo genome database (Table S1)
Summary
Lignin is the major component of the secondary cell wall and is the most abundant aromatic compound produced by plants. Lignin is more hydrophobic than cellulose, thereby playing a critical role in water transport in the xylem vessels [1,2]. Lignin plays a crucial role in plant defence [3]. Lignin is derived from the polymerisation of three phenylpropanoid monomers p-coumaryl, coniferyl and sinapyl alcohols called phydroxyphenyl (H), guaiacyl (G) and syringyl (S) monolignols, respectively [4]. The composition of monolignols is highly diverse across plant taxa, cell types, developmental stages and cell wall layers [5]. Lignin is polymerised from S and G monolignols in angiosperms, whereas in gymnosperms, lignin is composed of purely G lignin [5]
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