Identification of a novel genetically controlled step in mycorrhizal colonization: plant resistance to infection by fungal spores but not extra‐radical hyphae

Abstract

SummaryVesicular arbuscular mycorrhizal fungi infect plants by means of both spores and vegetative hyphae at early stages of symbiosis. Using 2500 M2 fast-neutron-mutagenized seeds of the miniature tomato (Lycopersicon esculentum) cultivar, Micro-Tom, we isolated a mutant, M161, that is able to resist colonization in the presence of Glomus intraradices spores. The myc ± phenotype of the mutant was stable for nine generations, and found to segregate as a single Mendelian recessive locus. The mutant exhibited morphological and growth-pattern characteristics similar to those of wild-type plants.Alterations of light intensity and day/night temperatures did not eliminate the myc ± characteristic.Resistance to mycorrhizal fungal infection and colonization was also evident following inoculation with the fungi Glomus mosseae and Gigaspora margarita. Normal colonization of M161 was evident when mutant plants were grown together with arbuscular mycorrhizal-inoculated wild-type plants in the same growth medium. During evaluation of the pre-infection stages in the mutant rhizosphere, spore germination and appressoria formation of G. intraradices were lower by 45 and 70%, respectively, than the rates obtained with wild-type plants. These results reveal a novel, genetically controlled step in the arbuscular mycorrhizal colonization process, governed by at least one gene, which signi®cantly reduces key steps in pre-mycorrhizal infection stages.

Symbiotic relationships between soil fungi and plants reduce N2O emissions from soil

“…The BC1 mutant exhibits a strongly reduced AMF root colonization compared to its wild-type progenitor (Meissner et al, 1997). This mutant/wild-type pair was created by fast-neutron mutagenization (David-Schwartz et al, 2001) and hybridization and has been demonstrated to be very suitable for studies in AMF ecology (Rillig et al, 2008). The tomato seeds were germinated in a sterilized 1:1 (v/v) sand-soil mixture and then transplanted into the microcosms.…”

Reduced arbuscular mycorrhizal colonization in tomato ethylene mutants

“…Non-mycorrhizal control treatments were inoculated with a mixture of soil and non-mycorrhizal B. decumbens roots (10 g). Phosphate was supplied twice a week as KH 2 PO 4 in solution to a final concentration of 4 or 40 mg P kg -1 substrate, for low and high P conditions, respectively (David-Schwartz et al, 2001). Treatments were arranged in fully randomized blocks, with eight replicate plants for mycorrhizal and three for non-mycorrhizal treatments.…”

NENA, a Lotus japonicus Homolog of Sec13, Is Required for Rhizodermal Infection by Arbuscular Mycorrhiza Fungi and Rhizobia but Dispensable for Cortical Endosymbiotic Development

“…Disruption of common SYM genes typically results in the abortion of fungal infection in the epidermal root layer (Kistner et al, 2005). In addition, dissection of AM development by forward genetic screens in tomato (Solanum lycopersicum), maize (Zea mays), or petunia (Petunia hybrida) discerned two additional stages (before fungal infection and during root colonization) that are controlled by the plant (Barker et al, 1998;David-Schwartz et al, 2001;Paszkowski et al, 2006;Reddy et al, 2007). We initiated a genetic screen for AM mutants in Lotus and identified the gene NENA, encoding a WD40 repeat nucleoporin required for AM fungal infection and RNS.…”