Oligogalacturonides, produced by enzymatic degradation of sugar beet by-products, confer partial protection against wheat powdery mildew

Nowadays, it becomes urgent to use new alternative strategies for a more sustainable agriculture, by developing eco-friendly biocontrol compounds leading to an induction of plant resistance against pathogens. In recent years, oligogalacturonides (OGs), fragments of pectin resulting from the degradation of the plant cell wall, have been particularly under focus for their ability to induce plant defense, leading to plant protection against pathogens. In the current work, 2 mixtures of OGs, bio-sourced from sugar beet by-products, were produced and assessed for their protective efficacy on wheat against Blumeria graminis f. sp. tritici (Bgt), responsible for powdery mildew. These OGs pools were obtained by hydrolysing pectins with two A. thaliana polygalacturonases (PGs), ADPG2 and PGLR (EC 3.2.1.15), produced in heterologous system Pichia pastoris. No direct effect of OGs generated by either ADPG2, named OGs-ADPG2 (degree of polymerisation/DP 1-10 and degree of esterification/DE 41%) or PGLR, named OGs-PGLR (DP 1-16, DE 34 %), was observed on Bgt spore germination in vitro. After a preventive foliar spraying of wheat by OGs, only OGs-PGLR provided a 31 % partial protection against Bgt. Both pools of OGs triggered an increase in the expression of some plant defense-related genes (peroxidase or PR proteins encoding genes), before inoculation with the pathogen. However, only OGs-PGLR induced the expression of a gene encoding a lipoxygenase (LOX), which is the first enzyme involved in the octadecanoic pathway, leading to oxylipins production in plant defense. Taking together, these findings revealed that some OGs, produced from sugar beet by-products by enzymatic hydrolysis, could be used as an alternative of phytochemicals.