Antisense Inhibition of Caffeic Acid 3-O-Methyltransferase (COMT) in Transgenic Sugarcane

Sugarcane is the most important crop used for bioenergy production in Brazil. The high sucrose content is the main source for sugar and ethanol production. However, it is expected a high increase of ethanol production also by using bagasse and trash from the field. This new process requires studies on suitable biomass for the industry with the development of technologies for high yield and low lignin content plants to make feasible the use of most of the cell wall as a carbon source.  Thus, the main objective of this work was to produce transgenic sugarcane showing antisense inhibition of the enzyme caffeic acid 3-O-methyltransferase (COMT) gene, which is one of the key enzyme in the lignin biosynthesis. Immature leaf roll discs of the varieties RB 835486 and SP80-3280 were co-transformed with nptII gene as selectable marker and an antisense fragment of COMT (COMT-AS), both were controlled by the maize ubi1 promoter. After bombardment the leaf discs were transferred to regeneration medium which consisted of the MS salts supplemented with BAP (0,5 mg/l) and NAA (0,1 mg/l) and geneticin (30 mg/L), in the light for 3 days prior transfer to MS medium with the selective agent. Sugarcane transformation was confirmed on 50 plants by PCR after 40-45 days on selective medium. Results of Real Time RT-PCR revealed that COMT expression levels were down regulated in 75% of transgenic plants of cultivar SP80-3280 (24 plants) and 50% of cultivar RB 835486 (8 plants). In both varieties, the lowest levels of expression were up to 16 times when compared to the control not transformed plants. Molecular and biochemical analyses are in process to verify the effects of COMT suppression in these transgenic sugarcane plants.