Downregulation of Maize Cinnamoyl‐Coenzyme A Reductase via RNA Interference Technology Causes Brown Midrib and Improves Ammonia Fiber Expansion‐Pretreated Conversion into Fermentable Sugars for Biofuels

Abstract

ABSTRACTConversion of lignocellulosic biomass into fermentable sugars for biofuels requires expensive pretreatment processes involving the breakdown of the cell wall structure and/or removal of lignin to increase accessibility of enzymes to the crop structural carbohydrates. Lignin is synthesized from precursors through a complex biosynthesis pathway. One of the important enzymes in this pathway is cinnamoyl‐coenzyme A reductase (CCR), which catalyzes the transformation of feruloyl and p‐coumaryl thioesters to their respective aldehydes. In an attempt to reduce lignin content and potentially accelerate deconstruction of maize (Zea mays L.) stover structural carbohydrates into fermentable sugars, expression of maize CCR (ZmCCR1; EC 1.2.1.44) was downregulated via ribonucleic acid interference (RNAi). Thirty first generation independent ZmCCR1_RNAi transgenic lines were produced. Among 10 out of 30 randomly tested, six lines showed significantly reduced ZmCCR1 transcription. The second generation of these ZmCCR1 downregulated transgenic plants exhibited brown coloration of midribs, husk, and stems and 7.0 to 8.7% reduction in Klason lignin. Also, crystalline cellulose was slightly increased in the lignin downregulated maize stover and further increased conversion of the ammonia fiber expansion (AFEX)‐pretreated maize stover into fermentable sugars. The third generation of CCR downregulated plants showed further reduced CCR transcription as compared to their second generation of transgenic (T1) plants.