Biodegradation Profiles of Proanthocyanidin-Accumulating Alfalfa Plants Coexpressing Lc- bHLH and C1-MYB Transcriptive Flavanoid Regulatory Genes.

Abstract

The utilization of the nutrient potential of alfalfa ( Medicago sativa L.) cannot be maximized because of its rapidly degradable protein content in the rumen, leading to waste and various digestive disorders. This might be alleviated if protein-binding proanthocyanidins are present in aerial parts of alfalfa forage in adequate amounts. The Lc (bHLH) and C1 (MYB) genes of maize are transcription factors known to be collectively involved in the regulation of anthocyanin biosynthetic pathways. The objective of this study was to investigate the effect of Lc and C1 gene transformations on the proanthocyanidin content, nutrient composition, and degradation characteristics of proteins and carbohydrates by comparing the transgenic alfalfa with its parental nontransgenic (NT) alfalfa and commercial AC-Grazeland cultivar. The DNA extracted from transgenic plants was tested for the presence of respective transgenes by amplification with specific primers of respective transgenes using PCR. Both Lc-single and LcC1-double transgenic alfalfa accumulated both monomeric and polymeric proanthocyanidins with total proanthocyanidins ranging from ca. 460 to 770 μg/g of DM. The C1-transgenic alfalfa did not accumulate proanthocyanidins similar to NT alfalfa. The C1 gene increased the NPN content significantly only in C1-single and Lc1C1-double transgenic alfalfa. The LcC1 combination seemed to have a synergic effect on reducing sugar in alfalfa. In contrast, the Lc gene appears to have a negative effect on starch content. The C1 gene tended to lower the PB3 content irrespective of the presence of the Lc gene. Although the cotransformation of Lc and C1 increased the total N/CHO ratio compared to Lc single gene transformation, the total N/CHO ratio of transgenic alfalfa was not significantly different from NT. In conclusion, Lc-bHLH single and LcC1 double gene transformation resulted in the accumulation of proanthocyanidins and affected the chemical profiles in alfalfa, which altered ruminal degradation patterns and impacted the nutrient availability of alfalfa in ruminant livestock systems.