A Common Signaling Process that Promotes Mycorrhizal and Oomycete Colonization of Plants

Abstract

The symbiotic association between plants and arbuscular mycorrhizal fungi is almost ubiquitous within the plant kingdom, and the early stages of the association are controlled by plant-derived strigolactones acting as a signal to the fungus in the rhizosphere and lipochito-oligosaccharides acting as fungal signals to the plant. Hyphopodia form at the root surface, allowing the initial invasion, and this is analogous to appressoria, infection structures of pathogenic fungi and oomycetes. Here, we characterize RAM2, a gene of Medicago truncatula required for colonization of the root by mycorrhizal fungi, which is necessary for appropriate hyphopodia and arbuscule formation. RAM2 encodes a glycerol-3-phosphate acyl transferase (GPAT) and is involved in the production of cutin monomers. Plants defective in RAM2 are unable to be colonized by arbuscular mycorrhizal fungi but also show defects in colonization by an oomycete pathogen, with the absence of appressoria formation. RAM2 defines a direct signaling function, because exogenous addition of the C16 aliphatic fatty acids associated with cutin are sufficient to promote hyphopodia/appressoria formation. Thus, cutin monomers act as plant signals that promote colonization by arbuscular mycorrhizal fungi, and this signaling function has been recruited by pathogenic oomycetes to facilitate their own invasion.

Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

“…These data are in accordance with the "birdsfoot" arbuscules described by Gutjahr and Parniske (2013) Feddermann et al, 2010), RAM2 (Wang et al, 2012), VAMP72s (Ivanov et al, 2012), SYP132A (Pan et al, 2016), EXO70I (Zhang et al, 2015), VTI12 (Lota et al, 2013), ERF1 (Devers et al, 2013), RED (Groth et al, 2013;Gutjahr and Parniske, 2013), RAM1/ATA (Rich et al, 2015), RAD1 (Park et al, 2015;Xue et al, 2015), and FatM (Bravo et al, 2016). Hence, P inhibition may be related to the functions of these genes.…”

Gibberellins Interfere with Symbiosis Signaling and Gene Expression and Alter Colonization by Arbuscular Mycorrhizal Fungi in Lotus japonicus

“…CM1852.30.r2; Gobbato et al, 2012], two RAM2 genes, Glycerol-3-phosphate acyltransferase1 [GPAT1; CM0905.50. r2] and GPAT2 [CM0905.160.r2; Wang et al, 2012], and Vapyrin1 [Vpy1]; Pumplin et al, 2010]), chitinase, lipase, and germin-like protein genes were up-regulated in the host root (Table I; Supplemental Table S1), indicating that our transcriptome analysis detected arbuscular mycorrhiza-induced genes. A number of GA biosynthesis gene homologs were up-or down-regulated during arbuscular mycorrhiza (Table I), including ent-kaurene oxidase, GA 20-oxidase (GA20ox), and GA 3-oxidase (GA3ox) homologs.…”

“…We also analyzed the effects of GA on the expression of the arbuscular mycorrhiza-induced genes SbtM1, RAM1, GPAT, and Vpy1, because knockdowns or knockouts of these genes affect AM colonization in L. japonicus and Medicago truncatula Pumplin et al, 2010;Gobbato et al, 2012;Wang et al, 2012). Either decreased or increased GA levels reduce AM fungal colonization in the roots (Fig.…”

Deciphering the Responses of Root Border-Like Cells of Arabidopsis and Flax to Pathogen-Derived Elicitors

“…Whereas mechanisms of plant defense involving the aerial parts are well documented, there is little knowledge of root responses to soil-borne pathogens (Attard et al, 2010;Millet et al, 2010;Lakshmanan et al, 2012;Wang et al, 2012). Extrapolation of defense responses from the leaves to the root system should be used carefully, since growing evidence suggests that molecular mechanisms are quite different between roots and aerial organs (Attard et al, 2010;Millet et al, 2010).…”