Genome-wide exploration of silicon (Si) transporter genes, <Emphasis Type="Italic">Lsi1</Emphasis> and <Emphasis Type="Italic">Lsi2</Emphasis> in plants; insights into Si-accumulation status/capacity of plants

Silicon (Si) is a nonessential, beneficial micronutrient for plants. It increases the plant stress tolerance in relation to its accumulation capacity. In this work, root Si transporter genes were characterized in 17 different plants and inferred for their Si-accumulation status. A total of 62 Si transporter genes (31 Lsi1 and 31 Lsi2) were identified in studied plants. Lsi1s were 261–324 residues protein with a MIP family domain whereas Lsi2s were 472–547 residues with a citrate transporter family domain. Lsi1s possessed characteristic sequence features that can be employed as benchmark in prediction of Si-accumulation status/capacity of the plants. Silicic acid selectivity in Lsi1s was associated with two highly conserved NPA (Asn-Pro-Ala) motifs and a Gly-Ser-Gly-Arg (GSGR) ar/R filter. Two NPA regions were present in all Lsi1 members but some Ala substituted with Ser or Val. GSGR filter was only available in the proposed high and moderate Si accumulators. In phylogeny, Lsi1s formed three clusters as low, moderate and high Si accumulators based on tree topology and availability of GSGR filter. Low-accumulators contained filters WIGR, AIGR, FAAR, WVAR and AVAR, high-accumulators only with GSGR filter, and moderate-accumulators mostly with GSGR but some with A/CSGR filters. A positive correlation was also available between sequence homology and Si-accumulation status of the tested plants. Thus, availability of GSGR selectivity filter and sequence homology degree could be used as signatures in prediction of Si-accumulation status in experimentally uncharacterized plants. Moreover, interaction partner and expression profile analyses implicated the involvement of Si transporters in plant stress tolerance.     

Antiviral activity of an N-allyl acridone against dengue virus

Background

Dengue virus (DENV), a member of the family Flaviviridae, is at present the most widespread causative agent of a human viral disease transmitted by mosquitoes. Despite the increasing incidence of this pathogen, there are no antiviral drugs or vaccines currently available for treatment or prevention. In a previous screening assay, we identified a group of N-allyl acridones as effective virus inhibitors. Here, the antiviral activity and mode of action targeted to viral RNA replication of one of the most active DENV-2 inhibitors was further characterized.

Results

The compound 10-allyl-7-chloro-9(10H)-acridone, designated 3b, was active to inhibit the in vitro infection of Vero cells with the four DENV serotypes, with effective concentration 50% (EC₅₀) values in the range 12.5-27.1 μM, as determined by virus yield inhibition assays. The compound was also effective in human HeLa cells. No cytotoxicity was detected at 3b concentrations up to 1000 μM. Mechanistic studies demonstrated that virus entry into the host cell was not affected, whereas viral RNA synthesis was strongly inhibited, as quantified by real time RT-PCR. The addition of exogenous guanosine together with 3b rescued only partially the infectivity of DENV-2.

Conclusions

The acridone derivative 3b selectively inhibits the infection of Vero cells with the four DENV serotypes without a direct interaction with the host cell or the virion but interfering specifically with the intracellular virus multiplication. The mode of antiviral action for this acridone apparently involves the cellular enzyme inosine-monophospahe dehydrogenase together with another still unidentified target related to DENV RNA synthesis.