Down-regulation of hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase, cinnamoyl CoA reductase, and cinnamyl alcohol dehydrogenase leads to lignin reduction in rice (Oryza sativa L. ssp japonica cv. Nipponbare)

Rice straw is one of the largest biomasses in the world that can potentially be exploited for biofuel. Nevertheless, the association of lignin with cellulose and hemicellulose has hindered the efficient utilization of rice straw for cellulosic biofuel. The objective of this study was to down-regulate key genes involved in lignin biosynthesis pathway, such as hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT), cinnamoyl CoA reductase (CCR), and cinnamyl alcohol dehydrogenase (CAD), through "terminator-less" constructs to reduce lignin in transgenic rice. Real-time qPCR analyses of the selected -T1 transgenic rice plants indicated 36-86% transcript reduction in HCT lines, 75-94% in CCR lines, and 10-85% in CAD lines. Of the nine down-regulated lines (three lines from each genes) subjected to lignin analysis, seven showed significant reduction in total lignin content (HCT-4, HCT-7, CAD-1, CAD-7, CCR-3, CCR-7, and CCR-12) with lignin reduction ranging from 4.6 to 10.8%. The results from this study indicated that truncated gene fragments lacking transcription termination sequence can be used for down-regulation of lignin genes in rice, and the rice straw from these transgenic lines could be useful as feedstock for cellulosic biofuel.