Abstract
Cinnamoyl-CoA reductase (CCR) is the first enzyme in the monolignol-specific branch of the lignin biosynthetic pathway. In this research, three sorghum CCR genes including SbCCR1, SbCCR2-1 and SbCCR2-2 were cloned and characterized. Analyses of the structure and phylogeny of the three CCR genes showed evolutionary conservation of the functional domains and divergence of function. Transient expression assays in Nicotiana benthamiana leaves demonstrated that the three CCR proteins were localized in the cytoplasm. The expression analysis showed that the three CCR genes were induced by drought. But in 48 h, the expression levels of SbCCR1 and SbCCR2-2 did not differ between CK and the drought treatment; while the expression level of SbCCR2-1 in the drought treatment was higher than in CK. The expression of the SbCCR1 and SbCCR2-1 genes was not induced by sorghum aphid [Melanaphis sacchari (Zehntner)] attack, but SbCCR2-2 was significantly induced by sorghum aphid attack. It is suggested that SbCCR2-2 is involved in the process of pest defense. Absolute quantitative real-time PCR revealed that the three CCR genes were mainly expressed in lignin deposition organs. The gene copy number of SbCCR1 was significantly higher than those of SbCCR2-1 and SbCCR2-2 in the tested tissues, especially in stem. The results provide new insight into the functions of the three CCR genes in sorghum.
Highlights
Lignin is a complex aromatic polymer present mainly in the secondary cell walls of vascular plants
The results showed that the expression levels of SbCCR1, SbCCR2-1 and SbCCR2-2 were significantly higher in the drought treatment than in CK at 24 h, indicating that all of the three Cinnamoyl-CoA reductase (CCR) genes were induced by drought
Phylogenetic analysis revealed that the SbCCR1 gene belongs to one clade, while SbCCR2-1 and SbCCR2-2 belong to another clade
Summary
Lignin is a complex aromatic polymer present mainly in the secondary cell walls of vascular plants. It plays an important role in specialized conducting and supporting tissues of plants, facilitating water transport, providing mechanical strength, and defending against biotic and abiotic stress (Bhuiyan et al, 2009; Vermerris, Sherman & McIntyre, 2010; Jin et al, 2014). The lignin biosynthetic pathway has attracted researchers’ attention because lignin is a limiting factor in a number of agro-industrial processes, such as chemical pulping, forage digestion, and the conversion of lignocellulosic plant biomass to bioethanol (Poovaiah et al, 2014; Tang et al, 2014). Lignin is derived from the polymerisation of monomeric subunits known as monolignols. The three main monolignols in grasses are p-coumaryl, coniferyl and sinapyl alcohols, which.
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