Title : Exploring the genetic diversity in tannin-rich forages to explain the large intra species variability in tannin content
Abstract:
Tannin-rich forages hold great potential in improving the environmental impact of ruminant production systems as they can reduce methane emissions by inhibiting enteric fermentation while simultaneously enhancing soil carbon sequestration by slowing decomposition and lowering ecosystem-level emissions. Previous studies have shown that the tannin containing forages big trefoil (BT; Lotus pedunculatus; contains Proanthocyanidins (PA)) and salad burnet (SB; Sanguisorba minor; contains hydrolysable tannins (HT)) are effective at doing so. However, their tannin content, and hence their bioactive properties, vary substantially and the genetic basis for the intraspecies variations in tannin content remain unclear. Establishing this link could ultimately allow the improvement of these species to be higher yielding and more bioactive. Thus, to understand the intraspecies variability in tannin content in SB and BT, and to identify loci responsible for said variability, we have characterised the polyphenol profile of 200 individuals of either species (400 plants) including tannin concentration, (and for PA also polymer size and, mean degree of polymerisation (mDP)), and flavanols. Five cultivars of SB and three of BT and were included in the study and were grown in greenhouse conditions. HT concentrations in SB ranged from 20.7 to 64.0 g/kg DM while PA concentrations in BT ranged from 5.1 to 28.6 g/kg DM, with an mDP between 9.8 and 17.1, demonstrating great intra and interspecies variability. The plants have subsequently been genotyped, a reference genome for each species constructed, and a genome wide association study (GWAS) is being conducted to identify single nucleotide polymorphisms (SNPs) associated with specific tannin profiles. To further validate potential loci in BT, differentially expressed genes between individuals and tissues expressing contrasting levels of tannin will be evaluated via RNA-seq. Potential functions of identified loci will be explored using the closely related and well-characterised Lotus japonicus. Identification of loci conferring greater bioactivity can facilitate breeding programmes of BT thereby enabling ruminant production system to approximate carbon neutrality when integrated into mixed grassland pastures.
