Progress towards developing bloat-safe legumes for the farming industry

Abstract

Proanthocyanidins (PAs) are polymeric flavonoids derived from the phenylpropanoid pathway, and they bind reversibly to forage proteins within the rumen, providing protection from bloat while enhancing protein utilisation and animal production. The occurrence of PAs varies greatly within forage legume species. Foliar PAs are present in Lotus corniculatus (birdsfoot trefoil) and Onobrychis viciifolia (sainfoin), but such species often show poor persistence under grazing. By contrast, Trifolium repens (white clover) and Medicago sativa (lucerne, or alfalfa) have good persistence but negligible amounts of foliar PAs. We altered the accumulation patterns present in lucerne and white clover by the overexpression of an R2R3-MYB transcription factor (TaMYB14) isolated from T. arvense (rabbit’s foot clover), a species with significant levels of leaf PA. Such plants effectively produced PAs of high degree of polymerisation (DP) in leaf tissue by upregulating genes of the PA pathway. By comparing transcriptome pools, we identified additional MYB transcription factors with putative involvement in PA synthesis in white clover and T. arvense, indicating that these species share a complex PA regulation system. Progress towards producing commercial cultivars of lucerne and white clover containing effective levels of PAs has begun. Such plants will provide a viable option for mitigating bloat in pastoral agriculture-based farming systems.