ARS | Publication request: Agronomic field evaluation of caffeic acid 3-O-methyltransferase and caffeoyl CoA 3-O-methyltransferase downregulated alfalfas

Submitted to: North American Alfalfa Improvement Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 17, 2006
Publication Date: July 17, 2006
Citation: Riday, H., Whalen, D.F., Bouton, J., Temple, S.J., Mccaslin, M., Dixon, R.A. 2006. Agronomic field evaluation of caffeic acid 3-O-methyltransferase and caffeoyl CoA 3-O-methyltransferase downregulated alfalfas. In: Proceedings of the 40th North American Alfalfa Improvement Conference and 19th Trifolum Conference, July 16-19, 2006, Minneapolis, Minnesota. Available at www.naaic.org/Meetings/National/2006meeting/procedings/Riday.PDF.

Technical Abstract: Alfalfa (Medicago sativa) is a widely used forage legume. Increasing alfalfa digestibility would increase forage value. One digestibility limitation in alfalfa is stem lignification, which presents an attractive target for genetic manipulation and selection. Lignin biosynthesis is controlled by the monolignal pathway and many of the genes involved in the pathway have been cloned in alfalfa. The alfalfa genes coding for caffeic acid 3-O-methyltransferase (COMT) and caffeoyl CoA 3-O-methyltransferase (CCOMT) have been identified. COMT regulates the production of S-lignin towards the end of the monolignal pathway. CCOMT regulates caffeoyl CoA to feruloyle CoA in the middle of the monolignal pathway. Alfalfa transgenics downregulated for COMT and CCOMT have been created. The objective of this study was to examine agronomic field performance of COMT and CCOMT downregulated alfalfas versus their unchanged counterparts in a high quality and lodging tolerant genetic background. Using the same plant callus line, 20 downregulation alfalfa transformants for COMT and CCOMT, as well as a null transformant, were generated. These 41 transformants were testcrossed to a high quality clone and a lodging tolerant clone both from Forage Genetics populations to generate 82 fullsib families. Confounding fullsib families and field replication, four fullsibs of each family were space transplanted at three locations: Prairie du Sac and West Salem, WI (Spring 2005) and Ardmore, OK (Autumn 2005). The following field traits were measured: biomass yield, crown diameter, fall dormancy, lodging (growth angle and score), maturity (flower and stem), moisture content, and plant height (standing and held). Forage quality was measured on the lower stems of harvested plants. Forage quality traits were predicted using the alfalfa whole plant NIRS consortium equation. As expected, downregulation of COMT and CCOMT decreased ADL and increased NDF digestibility (Table 1). However, downregulation of COMT and CCOMT resulted in plants with shorter stems compared to the null plants. Only downregulation of COMT resulted in increased stem lodging as measured by the stem growth angle. When compared to downregulating COMT, our findings suggest that downregulating CCOMT will increase alfalfa digestibility with fewer deleterious side effects.