Exploration of the Substrate Diversity of Leucoanthocyanidin Reductases

Proanthocyanidins (PAs) are mainly composed of epicatechin (EC) or catechin (C) subunits. C-type catechins (C and GC) are generally considered to be catalyzed by leucocyanidin reductase (LAR). In this study, we re-evaluated the function of LAR. LcLAR1 was isolated from Lotus corniculatus, which is rich in C-type catechins. Overexpression of LcLAR1 in tobacco resulted in a significantly increased content of EC and EC-glucoside. Overexpression of LcLAR1 in Arabidopsis thaliana promoted the accumulation of soluble PAs, including EC, PA dimers, and PA trimers. However, in the transgenic ans mutant overexpressing LcLAR1, the contents of C and C-glucoside were increased. In addition, overexpression of LcLAR1 in L. corniculatus resulted in a significant increase of C levels. Taken together, the products of LcLAR1 depended on the substrates, which revealed the substrate diversity of LcLAR1. Our study provides new insights into the flavonoid pathway, especially the role of LAR.