Restriction of Infection Threads in Nodulation of Clover and Lucerne

Clover and lucerne roots from plants grown in tube culture were examined for infection thread formation and nodule number. The number of infection threads was about equal to the number of nodules in Trifolium pratense L.; this relation was shown to hold for abundantly and sparsely nodulating plants and for bacterial inocula.nts producing large and small numbers of nodules.

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Infection thread formation as a basis of nodulation specificity in Rhizobium – strawberry clover associations

Canadian Journal of Microbiology ◽

10.1139/m69-206 ◽

1969 ◽

Vol 15 (10) ◽

pp. 1133-1136 ◽

Cited By ~ 27

Author(s):

Diana Li ◽

D. H. Hubbell

Keyword(s):

Characteristic Root ◽

Root Hairs ◽

Infection Thread ◽

Root Hair Deformation ◽

Infection Threads ◽

Specific Substance ◽

Thread Formation ◽

Nodulation Specificity ◽

Infection Thread Formation

The basis for determination of nodulating specificity in Rhizobium–clover associations was investigated. Thirteen strains of rhizobia from eight different cross-inoculation groups were used to inoculate aseptically grown strawberry clover seedlings in slide culture. Microscopic observation revealed that each strain produced characteristic root hair deformation but infection threads and nodules were observed only in the homologous combination. It is concluded that, in rhizobia–clover combinations which nodulate via infection threads, specificity is determined at or before infection thread initiation. Observations of other workers that rhizobia produce a strain-specific substance affecting growth and morphology of legume root hairs were confirmed by results of this study.

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The Ethylene Responsive Factor Required for Nodulation 1 (ERN1) Transcription Factor Is Required for Infection-Thread Formation in Lotus japonicus

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-11-16-0237-r ◽

2017 ◽

Vol 30 (3) ◽

pp. 194-204 ◽

Cited By ~ 29

Author(s):

Yasuyuki Kawaharada ◽

Euan K. James ◽

Simon Kelly ◽

Niels Sandal ◽

Jens Stougaard

Keyword(s):

Transcription Factor ◽

Root Nodule ◽

Lotus Japonicus ◽

Epidermal Cells ◽

Infection Thread ◽

Nod Factor ◽

Infection Threads ◽

Thread Formation ◽

Ethylene Responsive Factor ◽

Infection Thread Formation

Several hundred genes are transcriptionally regulated during infection-thread formation and development of nitrogen-fixing root nodules. We have characterized a set of Lotus japonicus mutants impaired in root-nodule formation and found that the causative gene, Ern1, encodes a protein with a characteristic APETALA2/Ethylene Responsive Factor (AP2/ERF) transcription-factor domain. Phenotypic characterization of four ern1 alleles shows that infection pockets are formed but root-hair infection threads are absent. Formation of root-nodule primordia is delayed and no normal transcellular infection threads are found in the infected nodules. Corroborating the role of ERN1 (ERF Required for Nodulation1) in nodule organogenesis, spontaneous nodulation induced by an autoactive CCaMK and cytokinin–induced nodule primordia were not observed in ern1 mutants. Expression of Ern1 is induced in the susceptible zone by Nod factor treatment or rhizobial inoculation. At the cellular level, the pErn1:GUS reporter is highly expressed in root epidermal cells of the susceptible zone and in the cortical cells that form nodule primordia. The genetic regulation of this cellular expression pattern was further investigated in symbiotic mutants. Nod factor induction of Ern1 in epidermal cells was found to depend on Nfr1, Cyclops, and Nsp2 but was independent of Nin and Nf-ya1. These results suggest that ERN1 functions as a transcriptional regulator involved in the formation of infection threads and development of nodule primordia and may coordinate these two processes.

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Exopolysaccharide Structure Is Not a Determinant of Host-Plant Specificity in Nodulation of Vicia sativa Roots

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-18-1123 ◽

2005 ◽

Vol 18 (11) ◽

pp. 1123-1129 ◽

Cited By ~ 16

Author(s):

Marc C. Laus ◽

Anton A. N. van Brussel ◽

Jan W. Kijne

Keyword(s):

Host Plant ◽

Rhizobium Leguminosarum ◽

Infection Thread ◽

Vicia Sativa ◽

Bacterial Growth Rate ◽

Successful Infection ◽

Infection Threads ◽

Thread Formation ◽

Host Plant Specificity ◽

Infection Thread Formation

Exopolysaccharide (EPS)-deficient strains of the root nodule symbiote Rhizobium leguminosarum induce formation of abortive infection threads in Vicia sativa subsp. nigra roots. As a result, the nodule tissue remains uninfected. Formation of an infection thread can be restored by coinoculation of the EPS-deficient mutant with a Nod factor-deficient strain, which produces a similar EPS structure. This suggests that EPS contributes to host-plant specificity of nodulation. Here, a comparison was made of i) coinoculation with heterologous strains with different EPS structures, and ii) introduction of the pRL1JI Sym plasmid or a nod gene-encoding fragment in the same heterologous strains. Most strains not complementing in coinoculation experiments were able to nodulate V. sativa roots as transconjugants. Apparently, coinoculation is a delicate approach in which differences in root colonization ability or bacterial growth rate easily affect successful infection-thread formation. Obviously, lack of infection-thread formation in coinoculation studies is not solely determined by EPS structure. Transconjugation data show that different EPS structures can allow infection-thread formation and subsequent nodulation of V. sativa roots.

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The Mesorhizobium loti purB Gene Is Involved in Infection Thread Formation and Nodule Development in Lotus japonicus

Journal of Bacteriology ◽

10.1128/jb.00788-07 ◽

2007 ◽

Vol 189 (22) ◽

pp. 8347-8352 ◽

Cited By ~ 18

Author(s):

Shin Okazaki ◽

Yoshiyuki Hattori ◽

Kazuhiko Saeki

Keyword(s):

Lotus Japonicus ◽

Infection Thread ◽

Nodule Development ◽

Nodule Formation ◽

Mesorhizobium Loti ◽

Infection Threads ◽

Thread Formation ◽

Infection Thread Formation

ABSTRACT The purB and purH mutants of Mesorhizobium loti exhibited purine auxotrophy and nodulation deficiency on Lotus japonicus. In the presence of adenine, only the purH mutant induced nodule formation and the purB mutant produced few infection threads, suggesting that 5-aminoimidazole-4-carboxamide ribonucleotide biosynthesis catalyzed by PurB is required for the establishment of symbiosis.

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