Arabinogalactan Protein-Like Proteins From Activate Immune Responses and Plant Resistance in an Oilseed Crop.

Natural compounds isolated from macroalgae are promising, ecofriendly, and multifunctional bioinoculants, which have been tested and used in agriculture. Ulvans, for instance, one of the major polysaccharides present in spp. cell walls, have been tested for their plant growth-promoting properties as well as their ability to activate plant immune defense, on a large variety of crops. Recently, we have characterized for the first time an arabinogalactan protein-like (AGP-like) from , which exhibits several features associated to land plant AGPs. In land plant, AGPs were shown to play a role in several plant biological functions, including cell morphogenesis, reproduction, and plant-microbe interactions. Thus, isolated AGP-like proteins may be good candidates for either the plant growth-promoting properties or the activation of plant immune defense. Here, we have isolated an AGP-like enriched fraction from and we have evaluated its ability to (i) protect oilseed rape () cotyledons against , and (ii) its ability to activate immune responses. Preventive application of the AGP-like enriched fraction on oilseed rape, followed by cotyledon inoculation with the fungal hemibiotroph , resulted in a major reduction of infection propagation. The noticed reduction correlated with an accumulation of HO in treated cotyledons and with the activation of SA and ET signaling pathways in oilseed rape cotyledons. In parallel, an ulvan was also isolated from . Preventive application of ulvan also enhanced plant resistance against . Surprisingly, reduction of infection severity was only observed at high concentration of ulvan. Here, no such significant changes in gene expression and HO production were observed. Together, this study indicates that AGP-like glycoproteins exhibit promising elicitor activity and that plant eliciting properties of extract, might result not only from an ulvan-originated eliciting activities, but also AGP-like originated.