TRANSFERRING THE TRAIT FOR LEAF PROANTHOCYANIDIN BIOSYNTHESIS FROM WILD TYPE TO CULTIVATED LOTUS HELPS IN UNDERSTANDING THE GENETIC CONTROL OF THESE SECONDARY METABOLITES AND BREEDING BLOAT-SAFE VARIETIES

PASSERI V; ESCARAY F J; DAMIANI F; PIECKENSTAIN F.L.; RUIZ O.A.; PAOLOCCI F.

Matera

Congreso; 54° ANNUAL CONGRESS SOCIETA’ ITALIANA DI GENETICA AGRARIA; 2010

SOCIETA’ ITALIANA DI GENETICA AGRARIA

Proanthocyanidins (PAs) are oligomeric and polymeric end products of the flavonoid biosynthetic pathway. The beneficial effects of PAs on human health and the significant pharmacological activities of PAs have been reviewed (Dixon et al. 2005). In planta, PAs act as protectants against pathogens, pests and diseases and additionally control seed permeability and dormancy. These compounds strongly affect plant quality traits and the palatability and nutritive value of forage legumes are highly influenced by their concentration and structure. High concentration of  PAs can decrease the palatability and digestibility of plants. Conversely, moderate quantities of PAs (2%-4% dry matter) in forage prevent proteolysis during ensiling and rumen fermentation, thereby protecting ruminants against pasture bloat. PAs therefore make the conversion of plant protein into animal protein more efficient with reduced methane production. However, among forage legumes only a few species area able to synthesize these secondary metabolites into the foliage. Therefore, the environmental and agronomical benefits that could be derived from triggering the accumulation of moderate amount of PAs in forage leaves are of considerable importance in the protection and nutrition of ruminants. Among legumes, Lotus species have a higher extent of genetic variability for accumulation of leaf proanthocyanidins (PAs), than Medicago and Trifolium spp. Indeed these two genus do not include species able to synthesize PAs in their foliage and metabolic engineering has failed thus far in inducing ex novo PA biosynthesis in these species. Among Lotus spp. Lotus corniculatus but not Lotus tenuis accumulates leaf PAs. With the aim to dissect the genetic control and molecular determinants of PAs we crossed plants belonging to a L. tenuis variety largely grown in South America with plants from a wild diploid population of L. corniculatus accumulating high levels of foliage PAs. Here we show that the leaf PA content in hybrid plants is between those of the parents and within the optimal range to prevent ruminal bloating. Interestingly, the expression of regulatory and structural genes of the PA pathway, such as a member of the R2R3MYB TT2 (TRANSPARENT TESTA 2) gene family and LAR (Leucoanthocyanidin reductase), respectively, highly correlated with the levels of leaf and stem PAs in the parents and hybrid plants. Conversely, the expression of other members of the Lotus TT2 gene family did not correlate with the level of PAs. Metabolic and molecular characterization of F2 plants is ongoing. Overall, L. tenuis x L. corniculatus plants provide us with a tool to gain insight into the inheritance and genetic control of PA biosynthesis in crop species as well as to breed bloat-safe Lotus varieties.