Two Lotus japonicus symbiosis mutants impaired at distinct steps of arbuscule development

Abstract

SUMMARYArbuscular mycorrhiza (AM) fungi form nutrient-acquiring symbioses with the majority of higher plants. Nutrient exchange occurs via arbuscules, highly branched hyphal structures that are formed within root cortical cells. With a view to identifying host genes involved in AM development, we isolated Lotus japonicus AM-defective mutants via a microscopic screen of an ethyl methanesulfonate-mutagenized population. A standardized mapping procedure was developed that facilitated positioning of the defective loci on the genetic map of L. japonicus, and, in five cases, allowed identification of mutants of known symbiotic genes. Two additional mutants representing independent loci did not form mature arbuscules during symbiosis with two divergent AM fungal species, but exhibited signs of premature arbuscule arrest or senescence. Marker gene expression patterns indicated that the two mutants are affected in distinct steps of arbuscule development. Both mutants formed wild-type-like root nodules upon inoculation with Mesorhizobium loti, indicating that the mutated loci are essential during AM but not during root nodule symbiosis.

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.…”

Lipid transfer from plants to arbuscular mycorrhiza fungi

“…Thus, RAM1, FatM, RAM2, STR and STR2 appear to form an AM-specific operational unit for lipid biosynthesis and transport in arbuscocytes. Consistently, they were found to be absent from genomes of plants that have lost the ability to form AM (Delaux et al, 2014;Favre et al, 2014;Bravo et al, 2016).Here, we analyzed two Lotus japonicus mutants from a forward genetics screen which are impaired in arbuscule branching (Groth et al, 2013). Positional cloning combined with genome resequencing revealed mutations in a novel AM-specific β-keto-acyl ACP 6 synthase I (KASI) gene and in the L. japonicus ortholog of M. truncatula RAM2.…”

“…We previously identified two L. japonicus mutants disorganized arbuscules (dis-1, SL0154-N) and SL0181-N deficient in arbuscule branching (Groth et al, 2013) ( Figure 1A-B). Both mutants also suffered from a reduction in root length colonization and blocked the formation of lipid-containing vesicles of the fungus Rhizophagus irregularis (Figure 1C-D).…”

“…Here, we analyzed two Lotus japonicus mutants from a forward genetics screen which are impaired in arbuscule branching (Groth et al, 2013). Positional cloning combined with genome resequencing revealed mutations in a novel AM-specific β-keto-acyl ACP 6 synthase I (KASI) gene and in the L. japonicus ortholog of M. truncatula RAM2.…”

Network of GRAS Transcription Factors Involved in the Control of Arbuscule Development inLotus japonicus

“…In addition, RNAi knockdown of VESICLE ASSOCIATED MEMBRANE PROTEIN72 in M. truncatula or SOLUBLE N-ETHYLMALEIMIDE-SENSITIVE FAC-TOR ATTACHMENT PROTEIN RECEPTOR family member L. japonicus VESICLE TRANSPORT THROUGH T-SNARE INTERACTION12 in L. japonicus led to distorted arbuscular development, which provided evidence for a role of these proteins in vesicle trafficking during arbuscule formation (Ivanov et al, 2012;Lota et al, 2013). Moreover, two L. japonicus mutants were reported to be affected in distinct steps of arbuscule development but not during RLS (Groth et al, 2013).…”