Analysis of arbuscular mycorrhizas using symbiosis‐defective plant mutants

Abstract

SummaryArbuscular mycorrhizas (AM), mutualistic plant-fungus symbioses formed on the majority of land plants, appear to play an important role in plant mineral nutrition, plant health, and might influence the structure of plant communities. Progress in understanding the genetic and molecular basis of this important symbiotic association has been hampered by the obligate biotrophy of the fungal partner, and by the lack of mycorrhiza formation on the plant model species Arabidopsis thaliana . Recently, legume plants, such as Medicago truncatula and Lotus japonicus , have been chosen as experimental systems for research of plant-microbe symbioses. The application of both reverse-and traditional forward-genetic approaches, in conjunction with genomics initiatives in model legumes, will rapidly increase our understanding of the plant-encoded genetic determinants of the arbuscular mycorrhiza. An essential step in this process has been the generation, isolation and analysis of mycorrhizal mutants. This review provides an introduction to existing plant mutants affected in AM formation.© New Phytologist (2001) 150 : 525 -532

Medicago truncatula plants overexpressing the early nodulin gene enod40 exhibit accelerated mycorrhizal colonization and enhanced formation of arbuscules

“…These findings indicate that enod40 may have a general role in mutualistic endosymbioses. This is in line with the genetic evidence, obtained from symbiosis-defective mutants, that certain sym genes of the host plant control both rhizobial and mycorrhizal symbioses (6,7).…”

“…These plants are especially interesting for research on plant-microbe interactions because they also live in symbiosis with rhizobial bacteria to form nitrogen-fixing root nodules (4,5). Although these two symbiotic interactions may appear rather different, several similarities have been reported during the colonization process (6,7). For example, certain f lavonoids of the host plant may act as signals promoting the establishment of the fungal as well as the rhizobial symbiosis (8).…”

“…Very little is known about plant genes that control mycorrhizal development and arbuscule formation (7), and so far no plant genes have been cloned that regulate the symbiosis with AM fungi. Here, we show that modification of enod40 expression affected mycorrhizal colonization and arbuscule formation in the root cortex.…”

Using mycorrhiza-defective mutant genotypes of non-legume plant species to study the formation and functioning of arbuscular mycorrhiza: a review

“…In this context, various alternative methods for establishing non-mycorrhizal 91 controls are summarised, before describing different non-legume plant species that 92 have mycorrhiza-defective mutant genotypes characterised and the nature of the 93 research they are used for. Emphasis is placed on non-legume mycorrhiza-defective 94 mutants as legume mycorrhiza-defective mutants have been reviewed in detail 95 previously (see Barker et al 2002;Marsh and Schultze 2001;Paszkowski 2006 have been described, both in legume and non-legume plant species (see Table 1 Maize roots that are colonised by AM fungi accumulate yellow pigment, which can be 140 detected macroscopically (Klingner et al 1995 There are a number of desirable phenotypes that need to be considered when 155 identifying potential mycorrhiza-defective mutant genotypes, and suitable criteria Table 1). 180 …”

Techniques for Arbuscular Mycorrhiza Inoculum Reduction

“…As a result these mutants have modified genes genes that play a role in both mycorrhiza formation and nodulation. Given the fact that nodulation is essentially restricted to one plant family, whereas AM are widespread, a significant number of mycorrhiza-specific genes must exist (Marsh and Schultze 2001), once they are identified, myc -mutants may became a more helpful tool for non-mycorrhizal controls.…”