The New Putative Type III Effector SkP48 in Bradyrhizobium sp. DOA9 is Involved in Legume Nodulation

Abstract Bradyrhizobium sp. DOA9 can nodulate a wide spectrum of legumes; however, unlike other bradyrhizobia, DOA9 carries a symbiotic plasmid harboring type III secretion system (T3SS) and several effector (T3E) genes, one of which encodes a new putative type III effector—SkP48. Here, we demonstrated the pivotal roles of SkP48 from Bradyrhizobium sp. DOA9 in inhibiting nodulation of various Vigna species and Crotalaria juncea and suppressing nodulation efficiency of Arachis hypogea. By contrast, the nodulation efficiency of a SkP48 mutant did not differ significantly with the DOA9 wild-type strain on Macroptilium atropurpureum and Stylosanthes hamata. An evolutionary analysis revealed that the SkP48 effector which contains a shikimate kinase and a SUMO protease (C48 cysteine peptidase) domain is distinct from the others effectors previously identified in others bradyrhizobia and pathogenic bacteria. Our findings suggest that the new putative T3E SkP48 is a key factor suppressing nodulation and nodule organogenesis in several legumes by activation of effector-triggered immunity through salicylic acid biosynthesis induction, which is deleterious to rhizobial infection. In addition, nodulation may be modulated by the function of defensins involved in jasmonic acid signalling in V. radiata SUT1.

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The Bradyrhizobium diazoefficiens type III effector NopE modulates the regulation of plant hormones towards nodulation in Vigna radiata

Scientific Reports ◽

10.1038/s41598-021-95925-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Pongdet Piromyou ◽

Hien P. Nguyen ◽

Pongpan Songwattana ◽

Pakpoom Boonchuen ◽

Kamonluck Teamtisong ◽

...

Keyword(s):

Salicylic Acid ◽

Plant Hormones ◽

Vigna Radiata ◽

Pathogenic Bacteria ◽

Evolutionary Analysis ◽

Host Genotype ◽

Type Iii Effectors ◽

Type Iii ◽

Calcium Dependent ◽

Symbiotic Interactions

AbstractHost-specific legume-rhizobium symbiosis is strictly controlled by rhizobial type III effectors (T3Es) in some cases. Here, we demonstrated that the symbiosis of Vigna radiata (mung bean) with Bradyrhizobium diazoefficiens USDA110 is determined by NopE, and this symbiosis is highly dependent on host genotype. NopE specifically triggered incompatibility with V. radiata cv. KPS2, but it promoted nodulation in other varieties of V. radiata, including KPS1. Interestingly, NopE1 and its paralogue NopE2, which exhibits calcium-dependent autocleavage, yield similar results in modulating KPS1 nodulation. Furthermore, NopE is required for early infection and nodule organogenesis in compatible plants. Evolutionary analysis revealed that NopE is highly conserved among bradyrhizobia and plant-associated endophytic and pathogenic bacteria. Our findings suggest that V. radiata and B. diazoefficiens USDA110 may use NopE to optimize their symbiotic interactions by reducing phytohormone-mediated ETI-type (PmETI) responses via salicylic acid (SA) biosynthesis suppression.

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Identification of novel Ralstonia solanacearum type III effector proteins through translocation analysis of hrpB-regulated gene products

Microbiology ◽

10.1099/mic.0.027763-0 ◽

2009 ◽

Vol 155 (7) ◽

pp. 2235-2244 ◽

Cited By ~ 33

Author(s):

Takafumi Mukaihara ◽

Naoyuki Tamura

Keyword(s):

Ralstonia Solanacearum ◽

Pathogenic Bacteria ◽

Tandem Repeats ◽

Plant Cells ◽

Secretion System ◽

Effector Proteins ◽

Gene Products ◽

Type Iii Effector ◽

Type Iii ◽

Effector Genes

The Hrp type III secretion system (TTSS) is essential for the pathogenicity of Ralstonia solanacearum on host plants. Hrp TTSS is a specialized secretion system that injects virulence proteins, the so-called type III effector proteins, into plant cells. In R. solanacearum, the expression of Hrp TTSS-related genes is regulated by an AraC-type transcriptional activator, HrpB. We have identified 30 hrpB-regulated hpx ( hrpB-dependent expression) genes and three well-known hrpB-regulated genes, popA, popB and popC, as candidate effector genes in R. solanacearum strain RS1000. In this study, we newly cloned 11 additional candidate effector genes that share homology with known hpx genes from R. solanacearum RS1000. Using a Cya reporter system, we investigated the translocation of these 44 gene products into plant cells via the Hrp TTSS and identified 34 effector proteins. These include three effector families composed of more than four members, namely the Hpx4, Hpx30 and GALA families. The Hpx30 family effectors are 2200–2500 aa in size and appear to be the largest class of effector proteins among animal- and plant-pathogenic bacteria. Members of this family contain 12–18 tandem repeats of a novel 42 aa motif, designated SKWP repeats.

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Identification and Functional Analysis of Type III Effector Proteins in Mesorhizobium loti

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-23-2-0223 ◽

2010 ◽

Vol 23 (2) ◽

pp. 223-234 ◽

Cited By ~ 46

Author(s):

Shin Okazaki ◽

Saori Okabe ◽

Miku Higashi ◽

Yoshikazu Shimoda ◽

Shusei Sato ◽

...

Keyword(s):

Pseudomonas Syringae ◽

Rhizobium Leguminosarum ◽

Plant Pathogens ◽

Effector Proteins ◽

Sequence Motif ◽

Shikimate Kinase ◽

Model Legume ◽

Type Iii Effector ◽

Mesorhizobium Loti ◽

Type Iii

Mesorhizobium loti MAFF303099, a microsymbiont of the model legume Lotus japonicus, possesses a cluster of genes (tts) that encode a type III secretion system (T3SS). In the presence of heterologous nodD from Rhizobium leguminosarum and a flavonoid naringenin, we observed elevated expression of the tts genes and secretion of several proteins into the culture medium. Inoculation experiments with wild-type and T3SS mutant strains revealed that the presence of the T3SS affected nodulation at a species level within the Lotus genus either positively (L. corniculatus subsp. frondosus and L. filicaulis) or negatively (L. halophilus and two other species). By inoculating L. halophilus with mutants of various type III effector candidate genes, we identified open reading frame mlr6361 as a major determinant of the nodulation restriction observed for L. halophilus. The predicted gene product of mlr6361 is a protein of 3,056 amino acids containing 15 repetitions of a sequence motif of 40 to 45 residues and a shikimate kinase-like domain at its carboxyl terminus. Homologues with similar repeat sequences are present in the hypersensitive-response and pathogenicity regions of several plant pathogens, including strains of Pseudomonas syringae, Ralstonia solanacearum, and Xanthomonas species. These results suggest that L. halophilus recognizes Mlr6361 as potentially pathogen derived and subsequently halts the infection process.

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