逆転写酵素・DNAポリメラーゼを用いたRT-PCRによる増幅反応で確認されたペッパーマイルドモットルウイルス（PMMoV）感染ピーマンの果実種子におけるウイルスの効果的な不活性化方法

A method for efficient inactivation Papper mild mottle virus (PMMoV) in harvested seeds of green pepper was examined based on the infectivity on the leaves of Nicotina glutinosa L.(a local host) and a reverse transcription and polymerase chain reaction (RT-PCR)-based amplification of the viral RNA. The seed homogenates from PMMoV-infected plants produced a large number of necrotic local lesion in N.glutinosa, but soaking the seeds in 10% (w/v) tri-sodium phosphate (Na3PO4) for 20 min or dry sterilization (70C,3h) effectivity eliminated the abundance of PMMoV. However, no necrotic lesion on N.glutinosa or the RT-PCR-basaed amplification was observed with seeds that has been disinfected by Na3PO4 in combination with dry sterilization

ピーマン(Capsicum annuum L.)に導入されたＬ２抵抗性遺伝子を打破する日本産トバモウイルス系統ペッパーマイルドモットルウイルス(PMMoV)の疫学的調査

To understand the epidemiological aspects of tobamovirus infecting the L resistance genotypes of green pepper, fifteen isolates were collected from geographically different fields and were chracterized by their biological properties. All isolates infected L1 and L2 plants systemically, but were localized in L3 and L4 plants. The symptomatology on several test plants and the reactivity to an antiserum showed that they were identical to that of a Japanese strain of pepper mild mottle virus (PMMoV-J). The viral infection was also confirmed by a reverse transcription and polymerase chain reaction (RT-PCR) with oligonucleotide primers that amplity the coat protein gene of PMMoV-RNA. On the other hand, the RT-PCR allowed us to detect PMMoV in seeds of some commercial cultivars of green pepper. Viruses isolated from the seeds could infect L2 plants systemically. Further analysis of the nucleotide sequence of the predicted coat protein gene revealed that the isolates from the commercial seeds were identical to that of PMMoV-J. These results indicated that the L2 resistance-breaking tobamovirus has prevailed in fields of green pepper in Japan. and that infected seeds may be one of the initial sources of the viral infection

Functional Characterization of Two Putative DAHP Synthases of AroG1 and AroG2 and Their Links With Type III Secretion System in Ralstonia solanacearum

Type three secretion system (T3SS) is essential for Ralstonia solanacearum to cause disease in host plants and we previously screened AroG1 as a candidate with impact on the T3SS expression. Here, we focused on two putative DAHP synthases of AroG1 and AroG2, which control the first step of the shikimate pathway, a common route for biosynthesis of aromatic amino acids (AAA), to characterize their functional roles and possible links with virulence in R. solanacearum. Deletion of aroG1/2 or aroG1, but not aroG2, significantly impaired the T3SS expression both in vitro and in planta, and the impact of AroG1 on T3SS was mediated with a well-characterized PrhA signaling cascade. Virulence of the aroG1/2 or aroG1 mutants was completely diminished or significantly impaired in tomato and tobacco plants, but not the aroG2 mutants. The aroG1/2 mutants failed to grow in limited medium, but grew slowly in planta. This significantly impaired growth was also observed in the aroG1 mutants both in planta and limited medium, but not in aroG2 mutants. Complementary aroG1 significantly restored the impaired or diminished bacterial growth, T3SS expression and virulence. Supplementary AAA or shikimic acid, an important intermediate of the shikimate pathway, significantly restored diminished growth in limited medium. The promoter activity assay showed that expression of aroG1 and aroG2 was greatly increased to 10-20-folder higher levels with deletion of the other. All these results demonstrated that both AroG1 and AroG2 are involved in the shikimate pathway and cooperatively essential for AAA biosynthesis in R. solanacearum. The AroG1 plays a major role on bacterial growth, T3SS expression and pathogenicity, while the AroG2 is capable to partially carry out the function of AroG1 in the absence of AroG1

The hrp genes of Pseudomonas cichorii are essential for pathogenicity on eggplant but not on lettuce

Pseudomonas cichorii causes necrotic lesions in eggplant and rot in lettuce. Through transposon insertion into P. cichorii strain SPC9018 we produced two mutants, 4-57 and 2-99, that lost virulence on eggplant but not lettuce. Analyses showed that a transposon was inserted into the hrpG gene in 4-57 and the hrcT gene in 2-99. Nucleotide sequences of the hrp genes of SPC9018 are homologous to those of Pseudomonas viridiflava BS group strains. The pathogenicity of 4-57 on eggplant was restored by transformation with an hrpF operon, originating from either SPC9018 or the BS group member P. viridiflava strain 9504 (Pv9504). These data suggested the involvement of hrp genes in the pathogenicity of SPC9018 on eggplant, and functional conservation of hrpF operons between SPC9018 and Pv9504. Both the hrpS mutant and the hrpL mutant were unable to cause necrotic lesions on eggplant leaves but retained their pathogenicity against lettuce. These results suggest that the pathogenicity of P. cichorii is hrp-dependent in eggplant, but not in lettuce

Editorial: Ralstonia solanacearum-Plant Interactions: Plant Defense Responses, Virulence Mechanisms and Signaling Pathways

In the Research Topic Ralstonia solanacearum-Plant Interactions: Plant Defense Responses, Virulence Mechanisms and Signaling Pathways, we aimed to collect manuscripts dealing with not only molecular mechanisms of R. solanacearum virulence and host responses but also development of the disease control system such as the disease-resistance cultivars and microbial inoculants..

Implications of Amino Acid Substitutions in GyrA at Position 83 in Terms of Oxolinic Acid Resistance in Field Isolates of Burkholderia glumae, a Causal Agent of Bacterial Seedling Rot and Grain Rot of Rice

Oxolinic acid (OA), a quinolone, inhibits the activity of DNA gyrase composed of GyrA and GyrB and shows antibacterial activity against Burkholderia glumae. Since B. glumae causes bacterial seedling rot and grain rot of rice, both of which are devastating diseases, the emergence of OA-resistant bacteria has important implications on rice cultivation in Japan. Based on the MIC of OA, 35 B. glumae field isolates isolated from rice seedlings grown from OA-treated seeds in Japan were divided into sensitive isolates (OSs; 0.5 μg/ml), moderately resistant isolates (MRs; 50 μg/ml), and highly resistant isolates (HRs; ≥100 μg/ml). Recombination with gyrA of an OS, Pg-10, led MRs and HRs to become OA susceptible, suggesting that gyrA mutations are involved in the OA resistance of field isolates. The amino acid at position 83 in the GyrA of all OSs was Ser, but in all MRs and HRs it was Arg and Ile, respectively. Ser83Arg and Ser83Ile substitutions in the GyrA of an OS, Pg-10, resulted in moderate and high OA resistance, respectively. Moreover, Arg83Ser and Ile83Ser substitutions in the GyrA of MRs and HRs, respectively, resulted in susceptibility to OA. These results suggest that Ser83Arg and Ser83Ile substitutions in GyrA are commonly responsible for resistance to OA in B. glumae field isolates

The Global Virulence Regulator PhcA Negatively Controls the Ralstonia solanacearum hrp Regulatory Cascade by Repressing Expression of the PrhIR Signaling Proteins▿ †

PhcA positively and negatively regulates many genes responsible for pathogenicity of Ralstonia solanacearum. The type III secretion system-encoding hrp regulon is one of the negatively controlled operons. PhcA bound to the promoter region of prhIR and repressed its expression, demonstrating that PhcA shuts down the most upstream component of a signal transfer system for hrpB activation