Regulation of Soybean Nodulation Independent of Ethylene Signaling1

Abstract

Leguminous plants regulate the number of Bradyrhizobium-or Rhizobium-infected sites that develop into nitrogen-fixing root nodules. Ethylene has been implicated in the regulation of nodule formation in some species, but this role has remained in question for soybean (Glycine max). The present study used soybean mutants with decreased responsiveness to ethylene, soybean mutants with defective regulation of nodule number, and Ag ؉ inhibition of ethylene perception to examine the role of ethylene in the regulation of nodule number. Nodule numbers on ethylene-insensitive mutants and plants treated with Ag ؉ were similar to those on wild-type plants and untreated plants, respectively. Hypernodulating mutants displayed wild-type ethylene sensitivity. Suppression of nodule numbers by high nitrate was also similar between ethyleneinsensitive plants, wild-type plants, and plants treated with Ag ؉ . Ethylene insensitivity of the roots of etr1-1 mutants was confirmed using assays for sensitivity to 1-aminocyclopropane-1-carboxylic acid and for ethylene-stimulated root-hair formation. Additional phenotypes of etr1-1 roots were also characterized. Ethylenedependent pathways regulate the number of nodules that form on species such as pea and Medicago truncatula, but our data indicate that ethylene is less significant in regulating the number of nodules that form on soybean.

Reactive oxygen species and ethylene play a positive role in lateral root base nodulation of a semiaquatic legume

“…Ethylene requirement is a special feature of S. rostrata nodulation. In Medicago sativa or Glycine max, nodulation was promoted or not influenced by ethylene inhibitors, respectively (8,9,36). Molecular data have confirmed the ethylene requirement: clones homologous to genes coding for S-adenosyl-L-methionine synthetases, 1-aminocyclopropane-1-carboxylate synthases and oxidases, which are three enzymes involved in ethylene synthesis, are up-regulated during intercellular invasion (unpublished data).…”

The Temperature-Sensitive brush Mutant of the Legume Lotus japonicus Reveals a Link between Root Development and Nodule Infection by Rhizobia

“…Ethylene contributes to the positioning of the nodule on the root (Heidstra et al, 1997). However, in soybean (Glycine max), the nodulation phenotype of ethyleneinsensitive mutants was indistinguishable from wild type (Schmidt et al, 1999). In Sesbania rostrata, ethylene positively acts on infection pocket and nodule primordium formation (D'Haeze et al, 2003).…”

Plant N Fluxes and Modulation by Nitrogen, Heat and Water Stresses: A Review Based on Comparison of Legumes and Non Legume Plants

“…This leads to an "autoregulation of nodulation" (called AON) and the www.intechopen.com control of nodule number by the host plant (Caetano-Anollès & Greshoff, 1990) through reciprocal shoot-root signalling (see Kinkema et al, 2006;Oka-kira & Kawaguchi, 2006 for review). Although the nature of the signals involved in the AON regulation has not been unambiguously elucidated, potential candidate compounds include either phytohormones, like ethylene (Schmidt et al, 1999), auxin (van Noorden et al, 2006) or brassinosteroids, jasmonic and abscisic acids (Oka-kira & Kawaguchi, 2006), or long distance signals involving the whole plant N status (Ruffel et al, 2008). Hypernodulating mutants, which are defective in AON, display excessive nodule numbers compared to wild type (Bourion et al, 2007) and maintain nodulation even when roots are exposed to nitrate.…”