Cloning and expression analysis of cinnamoyl-CoA reductase (CCR) genes in sorghum

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 includingSbCCR1,SbCCR2-1andSbCCR2-2were 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 inNicotiana benthamianaleaves 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 ofSbCCR1andSbCCR2-2did not differ between CK and the drought treatment; while the expression level ofSbCCR2-1in the drought treatment was higher than in CK. The expression of theSbCCR1andSbCCR2-1genes was not induced by sorghum aphid [Melanaphis sacchari(Zehntner)] attack, butSbCCR2-2was significantly induced by sorghum aphid attack. It is suggested thatSbCCR2-2is 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 ofSbCCR1was significantly higher than those ofSbCCR2-1andSbCCR2-2in the tested tissues, especially in stem. The results provide new insight into the functions of the three CCR genes in sorghum.