Compounds and genes for enhanced protein assimilation and digestibility in forage legumes: Altering condensed tannins content in the leaves of forage legumes

A large proportion of the protein present in alfalfa is lost in the rumen as a consequence of protolysis and deamination. This consequentially decreases animal productivity and in some instances causes pasture bloat, a chronic digestive disorder that is endemic to cattle. However, in vitro and in vivo studies of alternative forage species have shown that the presence of low levels (3-4%) of condensed tannins (CT, or proanthocyanidins) increase animal productivity and lessens the likelihood of pasture bloat. One aim of forage legume breeders is therefore to induce the accumulation of desirable levels of CT biosynthesis in CT negative forages such as white clover and alfalfa. However, interspecific crosses and somatic hybridisation have not achieved this goal. The European Union CAGED Project (Compounds And GEnes for enhanced protein assimilation and Digestibility of forage legumes-FAIR PL 98 4068, http://caged.irmgpf.pg.cnr.it/) takes a different approach to attain this goal. The aim of the project is to elucidate the biosynthetic pathway of CT synthesis by isolating and functionally assessing key genes from the CT pathway. This knowledge will guide our assessment of the options for modifying commercially grown forage legumes to express desirable levels of CT by use of modern breeding methodologies, gene-targeting and mutation. Central to our strategies is the CT accumulating species Lotus corniculatus. This model crop is a bone fide forage legume that is polymorphic for CT and is well adapted to in vitro manipulation and genetic transformation. We at IGER are collaborating with our colleagues at IRMGPF to isolate CT genes from L. corniculatus, characterising their regulation and evaluating their precise role in CT synthesis. In addition, we are closely involved with the Genetics and Breeding of Forage Legumes Group at INRA, who have extensive experience of forage digestibility and protein degradation analysis.