Distinct genetic bases for plant root responses to lipo-chitooligosaccharide signal molecules from distinct microbial origins

Abstract

SummaryLipo-chitooligosaccharides (LCOs) were originally found as symbiotic signals called Nod Factors (Nod-LCOs) controlling nodulation of legumes by rhizobia. More recently LCOs were also found in symbiotic fungi and, more surprisingly, very widely in the kingdom fungi including in saprophytic and pathogenic fungi. The LCO-V(C18:1, Fuc/MeFuc), hereafter called Fung-LCOs, are the LCO structures most commonly found in fungi. This raises the question of how legume plants, such as Medicago truncatula, can perceive and discriminate between Nod-LCOs and these Fung-LCOs.To address this question, we performed a Genome Wide Association Study on 173 natural accessions of Medicago truncatula, using a root branching phenotype and a newly developed local score approach.Both Nod- and Fung-LCOs stimulated root branching in most accessions but there was very little correlation in the ability to respond to these types of LCO molecules. Moreover, heritability of root response was higher for Nod-LCOs than for Fung-LCOs. We identified 123 loci for Nod-LCO and 71 for Fung-LCO responses, but only one was common.This suggests that Nod- and Fung-LCOs both control root branching but use different molecular mechanisms. The tighter genetic constraint of the root response to Fung-LCOs possibly reflects the ancestral origin of the biological activity of these molecules.

Long-lasting impact of chito-oligosaccharide application on strigolactone biosynthesis and fungal accommodation promotes arbuscular mycorrhiza inMedicago truncatula

“…Myc-factors include two classes of molecules: lipo-chito-oligosaccharides, or LCO (Maillet et al, 2011), structurally similar to rhizobial Nod-factors and composed of a short chitin chain with a few lateral substitutions; and chito-oligosaccharides, or CO (Genre et al, 2013), where only the chitin backbone is present. While LCO bioactivity has mostly been studied in legumes (Maillet et al, 2011;Sun et al, 2015;Bonhomme et al, 2021), CO are active in all tested AM host plants (Nasir et al, 2021) and their release is boosted upon strigolactone perception (Genre et al, 2013). Furthermore, CO can easily be produced through chitin hydrolysis (Crosino et al, 2021) making them particularly interesting for large scale agricultural applications (Volpe et al, 2020).…”